Asthma "of horses and men"--how can equine heaves help us better understand human asthma immunopathology and its functional consequences?

Heart rate variability in horses with and without severe equine asthma

BACKGROUND

Equine asthma in severe form (severe equine asthma [sEA]) shares remarkable similarities with human asthma. Human studies detected changes in the autonomic nervous system function in asthmatic patients based on heart rate variability (HRV) analysis.

STUDY DESIGN

Observational study.

OBJECTIVES

To investigate the relationship between sEA and HRV in horses.

METHODS

Twenty horses diagnosed with sEA and 20 asymptomatic (non-sEA) horses were investigated. SEA horses showed clinical signs. The RR intervals of the ECG were recorded for 1 h at rest between 9 AM and 11 AM using a heart rate (HR) monitor. HRV data were calculated using Kubios software. Parameters recorded for the sEA and non-sEA groups were compared using one-way MANOVA model. The significance level was set at α = 0.05.

RESULTS

SD2 (mean 99.6 ± SD 25.3 vs. 42.5 ± 17.1), SDNN (82.7 ± 20.7 vs. 41.3 ± 14.3), TINN (398.1 ± 104.9 vs. 209.3 ± 71.9), SD2/SD1 ratio (1.7 ± 0.2 vs. 1.1 ± 0.3), Total power (4740.2 ± 1977.9 vs. 1503.0 ± 1179.3), LF (2415.3 ± 1072.4 vs. 707.4 ± 649.9), SD1 (60.9 ± 15.9 vs. 39.2 ± 14.1), RMSSD (86.0 ± 22.6 vs. 55.3 ± 19.8) and HF (1575.8 ± 902.5 vs. 578.1 ± 491.1) were lower in sEA horses compared with the non-sEA horses (p < 0.01 for each variable). SD2, SDNN, TNN, the SD2/SD1 ratio and Total power showed the greatest discriminatory power in differentiating the sEA and non-sEA groups.

MAIN LIMITATIONS

Small sample size.

CONCLUSION

Our findings indicate that like humans, asthmatic horses show an overall reduction in autonomic control. A relative increase of the parasympathetic modulation of the heart was also observed. After further investigations, HRV measurement might be a non-invasive approach to monitor autonomic nervous system responses of sEA horses.

Exploring a pico-well based scRNA-seq method (HIVE) for simplified processing of equine bronchoalveolar lavage cells

Single-cell RNA sequencing (scRNA-seq) is a valuable tool for investigating cellular heterogeneity in diseases such as equine asthma (EA). This study evaluates the HIVE™ scRNA-seq method, a pico-well-based technology, for processing bronchoalveolar lavage (BAL) cells from horses with EA. The HIVE method offers practical advantages, including compatibility with both field and clinical settings, as well as a gentle workflow suited for handling sensitive cells. Our results show that the major cell types in equine BAL were successfully identified; however, the proportions of T cells and macrophages deviated from cytological expectations, with macrophages being overrepresented and T cells underrepresented. Despite these limitations, the HIVE method confirmed previously identified T cell and macrophage subpopulations and defined other BAL cell subsets. However, compared to previous studies T helper subsets were less clearly defined. Additionally, consistent with previous scRNA-seq studies, the HIVE method detected fewer granulocytes and mast cells than anticipated in the total BAL samples. Nevertheless, applying the method to purified mast cells recovered an expected number of cells. A small set of eosinophils were also detected which have not been characterized in earlier studies. In summary these findings suggest that while the HIVE method shows promise for certain applications, further optimization is needed to improve the accuracy of cell type representation, particularly for granulocytes and mast cells, in BAL samples.

Distinct Molecular Profiles Underpin Mild-To-Moderate Equine Asthma Cytological Profiles

A state-of-the-art multi-omics approach was applied to improve our understanding of the aetio-pathogenesis of a highly prevalent, performance-limiting disorder of racehorses: mild-to-moderate equine asthma (MMEA). This is a prerequisite to improving prophylactic, management, and therapeutic options for this condition. Although a number of risk factors have been identified, options for intervention are limited. This study applied a multi-omic approach to reveal key inflammatory pathways involved in inflammatory cell recruitment to the lower airways and highlight distinct MMEA inflammatory profiles. We compared bronchoalveolar lavage fluid (BALF) cell gene and protein expression data from horses with non-inflammatory BALF cytology with those isolated from horses with neutrophilic, mastocytic, mixed neutrophilic/mastocytic, and eosinophilic/mastocytic inflammation. The analyses on transcriptomic/proteomic data derived from BALF from horses with neutrophilic cytology showed enrichment in classical inflammatory pathways, and horses with mastocytic inflammation showed enrichment in pathways involved in hypersensitivity reactions related to nonclassical inflammation potentially mimicking a Th2-immune response. The mixed eosinophilic/mastocytic group also presented with a nonclassical inflammatory profile, whereas the mixed neutrophilic/mastocytic group revealed profiles consistent with both neutrophilic inflammation and hypersensitivity. Our adopted multi-omics approach provided a holistic assessment of the immunological status of the lower airways associated with the different cytological profiles of equine asthma.

Aspergillus fumigatus antigen-reactive Th17 cells are enriched in bronchoalveolar lavage fluid in severe equine asthma

Introduction

Equine asthma (EA) is a common disease of adult horses with chronic respiratory pathology and common neutrophilic airway inflammation. It presents with hyperreactivity to hay dust components such as molds, and underlying dysregulated T cell responses have been suggested. Thus far, T cells have been analysed in EA with conflicting results and the antigen reactivity of T cells has not been demonstrated. Serological and epidemiological data point to the relevance of Aspergillus fumigatus as an antigen source in EA. Here, we aimed to identify and characterise Aspergillus antigen-reactive T cells in EA.

Methods

Cryopreserved bronchoalveolar lavage cells (BALC) and peripheral blood mononuclear cells (PBMC) from healthy horses (HE, n=9) and those with mild-moderate (MEA, n=3) or severe asthma (SEA, n=8) were stimulated in vitro with the recombinant A. fumigatus antigens Asp f 1, or Asp f 7 combined with Asp f 8, to assess antigen reactivity, and with phorbol-12-myristat-13-acetate and ionomycin (P/i) to assess overall T cell reactivity. Stimulated cells were analysed by flow cytometry for CD4, CD8, IL-17, IL-4, and IFN-γ. Cytokine expression in all lymphocytes, and in CD4+ or CD8+ T cells, was quantified and compared between the groups. In BAL fluid (BALF), soluble cytokines and chemokines were quantified by bead-based assays.

Results

Antigen restimulation of BALC with Asp f 1 or Asp f 7/8 provoked higher frequencies of IL-17+ lymphocytes, CD4+IL-17+ Th17 cells, and CD4+IL-4+ Th2 cells in SEA than in HE, whereas MEA and HE were similar. Antigen stimulation of PBMC did not result in group differences. P/i stimulation of BALC resulted in increased IL-17+ lymphocyte and CD4+IL-17+ Th17 cell frequencies in MEA compared with HE but the limited number of horses with MEA must be considered. P/i-stimulated PBMC from MEA or SEA contained more IL-17+ lymphocytes compared with HE. Cytokines were hardly detected in BALF and similar between the groups but CCL2 and CCL5 concentrations were increased in BALF from SEA or MEA, respectively, compared with HE.

Conclusion

Horses with SEA have increased Aspergillus antigen-reactive Th17 cells in their airways, emphasising local T cell responses to this mold, which were quantified in EA for the first time here.

Lipids in Equine Airway Inflammation: An Overview of Current Knowledge

Mild-moderate and severe equine asthma (MEA and SEA) are prevalent inflammatory airway conditions affecting horses of numerous breeds and disciplines. Despite extensive research, detailed disease pathophysiology and the differences between MEA and SEA are still not completely understood. Bronchoalveolar lavage fluid cytology, broadly used in clinical practice and in equine asthma research, has limited means to represent the inflammatory status in the lower airways. Lipidomics is a field of science that can be utilized in investigating cellular mechanisms and cell-to-cell interactions. Studies in lipidomics have a broad variety of foci, of which fatty acid and lipid mediator profile analyses and global lipidomics have been implemented in veterinary medicine. As many crucial proinflammatory and proresolving mediators are lipids, lipidomic studies offer an interesting yet largely unexplored means to investigate inflammatory reactions in equine airways. The aim of this review article is to collect and summarize the findings of recent lipidomic studies on equine airway inflammation.

Comparative study of the bronchodilator efficacy and adverse effects of salbutamol and hyoscine butylbromide in horses with severe asthma

BACKGROUND

Salbutamol and hyoscine butylbromide (HBB) are commonly used bronchodilators in horses with severe asthma (SA).

OBJECTIVE

To compare the bronchodilation potency, duration, and adverse effects of salbutamol and HBB in SA.

ANIMALS

Six horses in exacerbation of SA.

METHODS

The effects of inhaled salbutamol (1000 μg) and HBB (150 mg, IV) were compared in a randomized, blinded, crossover experiment. Lung function, intestinal borborygmi and heart rate were assessed before and sequentially until 180 minutes after drug administration, and analyzed with 2-way repeated-measures ANOVA and Dunnett's multiple comparison tests.

RESULTS

Both treatments caused a similar improvement in lung function. Pulmonary resistance and reactance returned to baseline values within 30 minutes after HBB administration, whereas salbutamol improved reactance until 180 minutes (mean improvement at 180 minutes of 0.040 Kpa/L/s, 95% CI = 0.004 to 0.076; P = .02 for salbutamol and of 0.009 Kpa/L/s, 95% CI = -0.028 to 0.045; P = .98 for HBB for the resistance at 3 Hz and of 0.040 Kpa/L/s, 95% CI = 0.007 to 0.074; P = .01 for salbutamol and of 0.009 Kpa/L/s, 95% CI = -0.024 to 0.042; P = .97 for HBB for the reactance at 7 Hz). From 5 to 30 minutes after HBB administration, the heart rate accelerated (mean increase of 3.3 beats per minute, 95% CI = -6.6 to 13.1; P = .92 for salbutamol, and of 13.0 beats per minute, 95% CI = 3.6 to 22.4; P = .002 for HBB at 30 minutes) and the gut sounds decreased (mean reduction of 1.3, 95% CI = -0.1 to 2.8; P = .09 for salbutamol and of 2.8 for the gastrointestinal auscultation score, 95% CI = 1.4 to 4.3; P < .0001 for HBB at 30 minutes).

CONCLUSIONS AND CLINICAL IMPORTANCE

Both drugs have a similar bronchodilator potency but with a longer duration for salbutamol. Gastrointestinal and cardiovascular effects were noted only with HBB, suggesting the preferential use of salbutamol to relieve bronchoconstriction in horses with asthma.

Cytokine mRNA expression in the bronchoalveolar lavage cells from horses affected by different equine asthma subtypes

Equine asthma (EA) is a respiratory syndrome associated with the increase of different leukocyte populations in the bronchoalveolar lavage fluid (BALF). Its pathogenetic mechanisms remain unclear. This study aimed to evaluate the associations between the mRNA expression of different cytokines in the BALF, different EA subtypes and lung function. Fifteen horses underwent physical examination, airway endoscopy, BALF cytology and lung function testing (8/15). One horse did not have evidence of EA and was used as healthy reference, while the others were classified as affected by neutrophilic or mixed granulocytic EA. Cells isolated from the residual BALF were used for IL-1β, IL-2, IFN-γ, IL-4, IL-17A genes expression by quantitative RT-PCR., Cytokine expression was compared between groups, and their correlations with BALF leukocyte and lung function were evaluated. IL-1β expression was positively correlated with BALF neutrophils count (p=0.038, r=0.56) and with increased expiratory resistance (p=0.047, r=0.76). IFN-γ was correlated with BALF mast cells (p=0.029, r=0.58). IL-4 was higher in horses with mixed granulocytic EA than neutrophilic (p=0.008), positively correlated with BALF mast cells (p=0.028, r=0.59) and inversely with whole-breath (p=0.046, r=-0.76) and expiratory reactance (p=0.003, r=-0.93). Finally, IL-17A was inversely correlated with expiratory reactance (p=0.009, r=-0.92). These results support that multiple immune responses are involved in EA pathogenesis; innate, Th2, and Th17 responses. Innate immunity appeared associated with neutrophilic inflammation, and Th2 response with increased mast cells. The role of Th1 response in EA remains questionable.

Single-cell profiling of bronchoalveolar cells reveals a Th17 signature in neutrophilic severe equine asthma

Severe equine asthma (SEA) is a complex respiratory condition characterized by chronic airway inflammation. It shares many clinical and pathological features with human neutrophilic asthma, making it a valuable model for studying this condition. However, the immune mechanisms driving SEA have remained elusive. Although SEA has been primarily associated with a Th2 response, there have also been reports of Th1, Th17, or mixed-mediated responses. To uncover the elusive immune mechanisms driving SEA, we performed single-cell mRNA sequencing (scRNA-seq) on cryopreserved bronchoalveolar cells from 11 Warmblood horses, 5 controls and 6 with SEA. We identified six major cell types, including B cells, T cells, monocytes-macrophages, dendritic cells, neutrophils, and mast cells. All cell types exhibited significant heterogeneity, with previously identified and novel cell subtypes. Notably, we observed monocyte-lymphocyte complexes and detected a robust Th17 signature in SEA, with CXCL13 upregulation in intermediate monocytes. Asthmatic horses exhibited expansion of the B-cell population, Th17 polarization of the T-cell populations, and dysregulation of genes associated with T-cell function. Neutrophils demonstrated enhanced migratory capacity and heightened aptitude for neutrophil extracellular trap formation. These findings provide compelling evidence for a predominant Th17 immune response in neutrophilic SEA, driven by dysregulation of monocyte and T-cell genes. The dysregulated genes identified through scRNA-seq have potential as biomarkers and therapeutic targets for SEA and provide insights into human neutrophilic asthma.

Equine Asthma Does Not Affect Circulating Myostatin Concentrations in Horses

(1) Background: The number of horses suffering from chronic respiratory diseases, resembling human asthma, is increasing but there is still a lack of reliable and accurate methods to detect these disorders. Numerous studies have found elevated plasma concentrations of one of the myokines, namely, myostatin (MSTN), in people suffering from severe asthma. MSTN normally inhibits myoblast proliferation and differentiation through autocrine or paracrine signals. Therefore, given the pathogenesis of asthma, we hypothesize that MSTN could be a useful biomarker of equine asthma. Thus, this study aimed to compare the concentration of MSTN in the blood plasma of fully healthy and asthmatic horses. (2) Methods: A total of 61 horses were clinically examined to confirm or exclude the occurrence of equine asthma, including bronchoalveolar lavage (BAL) fluid cytology performed on 49 horses. This study included three groups of horses, two of which were clinically healthy, and one of which was asthmatic. (3) Results: The mean circulatory MSTN concentration determined using the ELISA method in asthmatic horses was significantly higher than that in clinically healthy young Thoroughbred racehorses (p < 0.05), but it did not differ as compared to the group of healthy, adult leisure horses. (4) Conclusions: The obtained results did not unambiguously support our original hypothesis that MSTM may be a reliable marker for the early diagnosis of equine asthma. To the best of the authors' knowledge, this is the first study to analyze the plasma MSTN concentration in equine asthma patients, and therefore further studies are needed to confirm our novel findings.

Neutrophil gelatinase-associated lipocalin as a potential biomarker for equine asthma

BACKGROUND

Studies in people have found neutrophil gelatinase-associated lipocalin (NGAL) concentrations are increased in asthma and can be used to distinguish between asthma subtypes. NGAL has not yet been investigated in equine asthma (EA).

OBJECTIVES

To investigate the ability of NGAL concentrations in bronchoalveolar lavage (BAL) fluid and serum to distinguish between control horses, horses with mild-moderate EA (MEA) and horses with severe EA (SEA).

STUDY DESIGN

Retrospective cross-sectional study.

METHODS

Details of endoscopic examination including tracheal mucus score (TMS, scale 0-5) and BAL cytology performed on 227 horses were extracted from records and NGAL concentrations were measured on stored serum and BAL fluid samples. The horses were divided into groups (control group n = 73, MEA n = 98, SEA n = 56) based on clinical signs and BAL cytology results. Differences between groups were evaluated with the Mann-Whitney test and correlation between BAL NGAL, serum NGAL, and BAL cytology were evaluated using Spearman's correlation.

RESULTS

BAL NGAL concentrations were higher in EA than in control horses (median: 25.6 and 13.3 μg/L, respectively, p < 0.001). Concentrations of NGAL in BAL differed between groups, with higher concentrations in MEA than in control horses (median: 18.5 and 13.3 μg/L, respectively, p < 0.001), and higher concentrations in SEA than in MEA horses (median: 54.1 and 18.5 μg/L, respectively, p < 0.001). BAL NGAL concentration differed between horses with TMS ≤2 an >2 (median 15.6 and 21.1 μg/L, respectively, p = 0.004). No differences were found in serum NGAL concentration between any of the groups.

MAIN LIMITATION

Only 66 of the 227 (29%) horses had haematology and serum NGAL measured.

CONCLUSION

BAL NGAL concentration differed between control and EA and reflected severity of disease. These results justify further research into the potential of NGAL as a biomarker of EA.

Microarray molecular mapping of horses with severe asthma

BACKGROUND

Severe asthma (SA) in horses, resembling human asthma, is a prevalent, debilitating allergic respiratory condition marked by elevated allergen-specific immunoglobulin E (IgE) against environmental proteins; however, research exploring the exposome's influence on IgE profiles is currently limited but holds paramount significance for diagnostic and therapeutic developments.

ANIMALS

Thirty-five sports horses were analyzed, consisting of environmentally matched samples from France (5 SA; 6 control), the United States (6 SA; 6 control), and Canada (6 SEA; 6 control).

METHODS

This intentional cross-sectional study investigated the sensitization profiles of SA-affected and healthy horses via serological antigen microarray profiling. Partial least square-discriminant analysis (PLS-DA) was used to identify and rank the importance of allergens for class separation (ie, affected/non-affected) as variable influence of projection (VIP), and allergen with commonality internationally established via frequency analysis.

RESULTS

PLS-DA models showed high discriminatory power in predicting SA in horses from Canada (area under the curve [AUC] 0.995) and France (AUC 0.867) but poor discriminatory power in horses from the United States (AUC 0.38). Hev b 5.0101, Cyn D, Der p 2, and Rum cr were the only shared allergens across all geographical groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

Microarray profiling can identify specific allergenic components associated with SA in horses, while mathematical modeling of this data can be used for disease classification, highlighting the variability of sensitization profiles between geographical locations and emphasizing the importance of local exposure to the prevalence of different allergens. Frequency scoring analysis can identify important variables that contribute to the classification of SA across different geographical regions.

Metabolomics in Animal Models of Bronchial Asthma and Its Translational Importance for Clinics

Bronchial asthma is an extremely heterogenous chronic respiratory disorder with several distinct endotypes and phenotypes. These subtypes differ not only in the pathophysiological changes and/or clinical features but also in their response to the treatment. Therefore, precise diagnostics represent a fundamental condition for effective therapy. In the diagnostic process, metabolomic approaches have been increasingly used, providing detailed information on the metabolic alterations associated with human asthma. Further information is brought by metabolomic analysis of samples obtained from animal models. This article summarizes the current knowledge on metabolomic changes in human and animal studies of asthma and reveals that alterations in lipid metabolism, amino acid metabolism, purine metabolism, glycolysis and the tricarboxylic acid cycle found in the animal studies resemble, to a large extent, the changes found in human patients with asthma. The findings indicate that, despite the limitations of animal modeling in asthma, pre-clinical testing and metabolomic analysis of animal samples may, together with metabolomic analysis of human samples, contribute to a novel way of personalized treatment of asthma patients.

Lipid species profiling of bronchoalveolar lavage fluid cells of horses housed on two different bedding materials

The lipidome of equine BALF cells has not been described. The objectives of this prospective repeated-measures study were to explore the BALF cells' lipidome in horses and to identify lipids associated with progression or resolution of airway inflammation. BALF cells from 22 horses exposed to two bedding materials (Peat 1-Wood shavings [WS]-Peat 2) were studied by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The effects of bedding on lipid class and species compositions were tested with rmANOVA. Correlations between lipids and cell counts were examined. The BALF cells' lipidome showed bedding-related differences for molar percentage (mol%) of 60 species. Whole phosphatidylcholine (PC) class and its species PC 32:0 (main molecular species 16:0_16:0) had higher mol% after Peat 2 compared with WS. Phosphatidylinositol 38:4 (main molecular species 18:0_20:4) was higher after WS compared with both peat periods. BALF cell count correlated positively with mol% of the lipid classes phosphatidylserine, sphingomyelin, ceramide, hexosylceramide, and triacylglycerol but negatively with PC. BALF cell count correlated positively with phosphatidylinositol 38:4 mol%. In conclusion, equine BALF cells' lipid profiles explored with MS-based lipidomics indicated subclinical inflammatory changes after WS. Inflammatory reactions in the cellular lipid species composition were detected although cytological responses indicating inflammation were weak.

Molecular and Cellular Evaluation of Horses With Summer Pasture Associated Asthma Syndrome

Equine asthma is an airway disease that affects a large number of horses annually leading to considerable economic losses in the horse industry. Despite advances in research in this area, there is still a lack of information on its etiology and molecular characterization in pasture associated asthma. The objective of the current study was to characterize the inflammatory disease of lower airways in horses maintained on pasture through cytologic and immunologic profile during the summer in a tropical environment by analysis of the gene expression of Th1 cytokines (IFN- λ, IL-8), Th2 cytokines (IL-4 and IL-5), and pro-inflammatory cytokines (IL-1, TNF-α) in the bronchoalveolar lavage (BAL) fluid in healthy and asthma horses on pasture. A group 39 of clinically healthy horses maintained on native pasture and supplemented with concentrate was evaluated by BAL analyzed for differential cellular count and assigned into a control and an asthma group. The gene expression of pro-inflammatory cytokines was analyzed in the BAL by reverse time PCR (RT-PCR) (IL-1α (alpha), IL-4, IL-5, IL-8, TNF-α alpha and IFN-λ), using β-actin as housekeeping gene. Higher gene expression of IL-1, IL-4, IL-5, IL-8, IFN-λ in the BAL of asthma horses was found. Current results indicate an increase in Th2, characterizing an allergic inflammatory reaction due to the significant increase in IL-5 in asthmatic horses (10.3 ± 1.13), when compared to the values ​​obtained in normal horses (3.27 ± 0.46). The only down regulated cytokine in the asthma group was TNF-α, suggesting a chronic antigenic reaction.

Single-cell transcriptomics delineates the immune cell landscape in equine lower airways and reveals upregulation of FKBP5 in horses with asthma

Equine asthma (EA) is a heterogenous, complex disease, with a significant negative impact on horse welfare and performance. EA and human asthma share fundamental similarities, making EA a useful model for studying the disease. One relevant sample type for investigating chronic lung inflammation is bronchoalveolar lavage fluid (BALF), which provides a snapshot of the immune cells present in the alveolar space. To investigate the immune cell landscape of the respiratory tract in horses with mild-to-moderate equine asthma (mEA) and healthy controls, single-cell RNA sequencing was conducted on equine BALF cells. We characterized the major immune cell populations present in equine BALF, as well as subtypes thereof. Interestingly, the most significantly upregulated gene discovered in cases of mEA was FKBP5, a chaperone protein involved in regulating the activity of the glucocorticoid receptor.

Fatty acid fingerprints in bronchoalveolar lavage fluid and its extracellular vesicles reflect equine asthma severity

Equine asthma (EA) is an inflammatory disease of the lower airways driven by mediators released from cells. Extracellular vesicles (EVs) are vehicles for lipid mediators, which possess either pro-inflammatory or dual anti-inflammatory and pro-resolving functions. In this study, we investigated how the respiratory fatty acid (FA) profile reflects airway inflammatory status. The FA composition of bronchoalveolar lavage fluid (BALF), BALF supernatant, and bronchoalveolar EVs of healthy horses (n = 15) and horses with mild/moderate EA (n = 10) or severe EA (SEA, n = 5) was determined with gas chromatography and mass spectrometry. The FA profiles distinguished samples with different diagnoses in all sample types, yet they were insufficient to predict the health status of uncategorized samples. Different individual FAs were responsible for the discrimination of the diagnoses in different sample types. Particularly, in the EVs of SEA horses the proportions of palmitic acid (16:0) decreased and those of eicosapentaenoic acid (20:5n-3) increased, and all sample types of asthmatic horses had elevated dihomo-γ-linolenic acid (20:3n-6) proportions. The results suggest simultaneous pro-inflammatory and resolving actions of FAs and a potential role for EVs as vehicles for lipid mediators in asthma pathogenesis. EV lipid manifestations of EA can offer translational targets to study asthma pathophysiology and treatment options.

Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology

BACKGROUND

Allergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens.

OBJECTIVES

To review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention.

MATERIALS AND METHODS

The authors reviewed the literature up to November 2022. Results were presented at North America Veterinary Dermatology Forum (2021) and European Veterinary Dermatology Congress (2021). The report was available to member organisations of the World Association for Veterinary Dermatology for feedback.

CONCLUSIONS AND CLINICAL RELEVANCE

Insect bite hypersensitivity (IBH) is the best characterised allergic skin disease. An immunoglobulin (Ig)E response against Culicoides salivary antigens is widely documented. Genetics and environmental factors play important roles. Tests with high sensitivity and specificity are lacking, and diagnosis of IBH is based on clinical signs, seasonality and response to insect control. Eosinophils, interleukin (IL)-5 and IL-31 are explored as therapeutic targets. Presently, the most effective treatment is insect avoidance. Existing evidence does not support allergen-specific immunotherapy (ASIT) using commercially available extracts of Culicoides. Hypersensitivity to environmental allergens (atopic dermatitis) is the next most common allergy. A role for IgE is supported by serological investigation, skin test studies and positive response to ASIT. Prospective, controlled, randomised studies are limited, and treatment relies largely on glucocorticoids, antihistamines and ASIT based on retrospective studies. Foods are known triggers for urticaria, yet their role in pruritic dermatitis is unknown. Recurrent urticaria is common in horses, yet our understanding is limited and focussed on IgE and T-helper 2 cell response. Prospective, controlled studies on treatments for urticaria are lacking. Glucocorticoids and antihistamines are primary reported treatments.

Induced pluripotent stem cells in companion animals: how can we move the field forward?

Following a one medicine approach, the development of regenerative therapies for human patients leads to innovative treatments for animals, while pre-clinical studies on animals provide knowledge to advance human medicine. Among many different biological products under investigation, stem cells are among the most prominent. Mesenchymal stromal cells (MSCs) are extensively investigated, but they present challenges such as senescence and limited differentiation ability. Embryonic stem cells (ESCs) are pluripotent cells with a virtually unlimited capacity for self-renewal and differentiation, but the use of embryos carries ethical concerns. Induced pluripotent stem cells (iPSCs) can overcome all of these limitations, as they closely resemble ESCs but are derived from adult cells by reprogramming in the laboratory using pluripotency-associated transcription factors. iPSCs hold great potential for applications in therapy, disease modeling, drug screening, and even species preservation strategies. However, iPSC technology is less developed in veterinary species compared to human. This review attempts to address the specific challenges associated with generating and applying iPSCs from companion animals. Firstly, we discuss strategies for the preparation of iPSCs in veterinary species and secondly, we address the potential for different applications of iPSCs in companion animals. Our aim is to provide an overview on the state of the art of iPSCs in companion animals, focusing on equine, canine, and feline species, as well as to identify which aspects need further optimization and, where possible, to provide guidance on future advancements. Following a "step-by-step" approach, we cover the generation of iPSCs in companion animals from the selection of somatic cells and the reprogramming strategies, to the expansion and characterization of iPSCs. Subsequently, we revise the current applications of iPSCs in companion animals, identify the main hurdles, and propose future paths to move the field forward. Transferring the knowledge gained from human iPSCs can increase our understanding in the biology of pluripotent cells in animals, but it is critical to further investigate the differences among species to develop specific approaches for animal iPSCs. This is key for significantly advancing iPSC application in veterinary medicine, which at the same time will also allow gaining pre-clinical knowledge transferable to human medicine.

Asthma: The Use of Animal Models and Their Translational Utility

Asthma is characterized by chronic lower airway inflammation that results in airway remodeling, which can lead to a permanent decrease in lung function. The pathophysiology driving the development of asthma is complex and heterogenous. Animal models have been and continue to be essential for the discovery of molecular pathways driving the pathophysiology of asthma and novel therapeutic approaches. Animal models of asthma may be induced or naturally occurring. Species used to study asthma include mouse, rat, guinea pig, cat, dog, sheep, horse, and nonhuman primate. Some of the aspects to consider when evaluating any of these asthma models are cost, labor, reagent availability, regulatory burden, relevance to natural disease in humans, type of lower airway inflammation, biological samples available for testing, and ultimately whether the model can answer the research question(s). This review aims to discuss the animal models most available for asthma investigation, with an emphasis on describing the inciting antigen/allergen, inflammatory response induced, and its translation to human asthma.

Initial investigation of molecular phenotypes of airway mast cells and cytokine profiles in equine asthma

Equine asthma is a naturally occurring lung disease characterized by chronic, partially reversible airway obstruction, pulmonary remodeling, and lower airway inflammation. Asthma is currently divided into two major groups, mild to moderate asthma (mEA) and severe asthma (sEA), but further subtyping by phenotype (i.e., clinical presentation) and/or endotype (i.e., cellular mechanisms) may be warranted. For this study, we were interested in further investigation of cellular and inflammatory characteristics of EA, including airway mast cells. The purpose of this study was to: (1) compare mast cell protease mRNA expression between healthy and asthmatic horses, (2) analyze the cytokine profile present in BALF of currently defined equine asthma groups, and (3) use these data to evaluate potential biomarkers of defined asthma groups. We hypothesized that there would be significant differences in the cellular mast cell phenotypes (i.e., mucosal vs. connective tissue) and cytokine profiles in the BALF of asthmatic vs. healthy horses and across asthma groups. We assert these characteristics may inform additional subtypes of equine asthma. Adult horses were recruited from the institution's teaching herd and clinical caseload. Mast cell protease gene expression of the BALF cellular component and multiplex bead immunoassay for cytokine concentrations in the BALF supernatant were investigated. Airway mast cells primarily expressed tryptase, with low levels of chymase. No significant changes in protease expression were detected across groups. Horses with severe asthma had increased TNF-α, CXCL-8, and IFN-γ concentrations in BALF supernatant. Multidimensional analysis demonstrated healthy and mEA horses have overlapping characteristics, with sEA separating from the other groups. This difference was primarily due to BALF neutrophil and lymphocyte concentrations. These study results further inform understanding of EA immunopathology, and future studies designed to investigate asthma phenotypes and endotypes. Ultimately, a better understanding of these groups could help identify novel therapeutic strategies.

Equine peripheral blood CD14+ monocyte-derived macrophage in-vitro characteristics after GM-CSF pretreatment and LPS+IFN-γ or IL-4+IL-10 differentiation

Macrophages are a heterogeneous population of immune cells that exhibit dynamic plasticity, polarize into inflammatory or regulatory/pro-resolving macrophages, and influence the healing tissue microenvironment. This study evaluated the in-vitro morphological, proliferative, cell surface marker expression and cytokine/soluble factor secretion characteristics of control, GM-CSF pretreated and inflammatory (LPS+IFN-γ) and regulatory (IL-4 + IL-10) differentiated equine CD14+ monocyte-derived macrophages. Phase contrast microscopy demonstrated that LPS+IFN-γ-primed macrophages exhibited a rounded, granular morphology, whereas IL-4 +IL-10-primed macrophages were elongated with a spindle-shaped morphology. GM-CSF enhanced the proliferation rate of monocytes/macrophages during adherent in-vitro culture. Flow cytometry analysis showed that GM-CSF alone and GM-CSF pretreatment with LPS+IFN-γ or IL-4 +IL-10 priming increased CD86 immunopositivity by 2-fold (p = 0.6); and CD206 immunopositivity remained unchanged. GM-CSF pretreatment and subsequent priming with LPS and IFN-γ yielded inflammatory macrophages that secrete significantly increased quantities of IL-1β compared to control (p = 0.012) and IL-4 +IL-10-primed (p = 0.0047) macrophages. GM-CSF pretreatment followed by both LPS + IFN-γ and IL-4 + IL-10 priming significantly increased IL-1Ra secretion by 6-fold (p < 0.05). There were no differences in TGFβ-1 secretion among control, LPS+IFN-γ or IL-4 + IL-10 primed macrophages (p = 0.85). All groups contained an average of 643 ± 51.5 pg/mL of TGFβ1. Among the culture conditions evaluated, IL-4 +IL-10 priming for 24 h after 6 days of adherent culture yielded macrophages that were the least inflammatory compared to GM-CSF pretreated and LPS+IFN-γ or IL-4 +IL-10-primed macrophages. These results provide a basis for subsequent in-vitro and in-vivo studies that investigate macrophage-tissue cell interactions and related biological mechanisms relevant to the field of immunomodulatory approaches for enhancing tissue healing.

Neutrophil Extracellular Vesicles and Airway Smooth Muscle Proliferation in the Natural Model of Severe Asthma in Horses

Extracellular vesicles (EVs) contribute to intercellular communication through the transfer of their rich cargo to recipient cells. The EVs produced by LPS-stimulated neutrophils from healthy humans and horses increase airway smooth muscle (ASM) proliferation, but the roles of neutrophil EVs in asthma are largely unexplored. The aim of this study was to determine whether neutrophil-derived EVs isolated during the remission or exacerbation of asthma influence ASM proliferation differentially. Peripheral blood neutrophils were collected during remission and exacerbation in eight horses affected by severe asthma. The cells were cultured (±LPS), and their EVs were isolated by ultracentrifugation and characterized by laser scattering microscopy and proteomic analysis. The proliferation of ASM co-incubated with EVs was monitored in real time by electrical impedance. Two proteins were significantly upregulated during disease exacerbation in neutrophil EVs (MAST4 and Lrch4), while LPS stimulation greatly altered the proteomic profile. Those changes involved the upregulation of neutrophil degranulation products, including proteases known to induce myocyte proliferation. In agreement with the proteomic results, EVs from LPS-stimulated neutrophils increased ASM proliferation, without an effect of the disease status. The inhalation of environmental LPS could contribute to asthma pathogenesis by activating neutrophils and leading to ASM hyperplasia.

Long-Read Transcriptome of Equine Bronchoalveolar Cells

We used Pacific Biosciences long-read isoform sequencing to generate full-length transcript sequences in equine bronchoalveolar lavage fluid (BALF) cells. Our dataset consisted of 313,563 HiFi reads comprising 805 Mb of polished sequence information. The resulting equine BALF transcriptome consisted of 14,234 full-length transcript isoforms originating from 7017 unique genes. These genes consisted of 6880 previously annotated genes and 137 novel genes. We identified 3428 novel transcripts in addition to 10,806 previously known transcripts. These included transcripts absent from existing genome annotations, transcripts mapping to putative novel (unannotated) genes and fusion transcripts incorporating exons from multiple genes. We provide transcript-level data for equine BALF cells as a resource to the scientific community.

Inhalative Nanoparticulate CpG Immunotherapy in Severe Equine Asthma: An Innovative Therapeutic Concept and Potential Animal Model for Human Asthma Treatment

Simple Summary

Severe equine asthma is the most common globally widespread non-infectious equine respiratory disease (together with its mild and moderate form), which is associated with exposure to hay dust and mold spores, has certain similarities to human asthma, and continues to represent a therapeutic problem. Immunomodulatory DNA sequences (CpG) bound to nanoparticles were successfully administered by inhalation to severe asthmatic horses in several studies. It was possible to demonstrate a significant, sustained, one-to-eight-week improvement in important clinical parameters: partial oxygen pressure in the blood, quantity and viscosity of tracheal mucus secretion in the airways, and the amount of inflammatory cells in the respiratory tracts of severe asthmatic horses. The immunotherapy with CpG is performed independent of specific allergens. At an immunological level, the treatment leads to decreases in allergic and inflammatory parameters. This innovative therapeutic concept thus opens new perspectives in severe equine asthma treatment and possibly also in human asthma treatment.

Abstract

Severe equine asthma is the most common globally widespread non-infectious equine respiratory disease (together with its mild and moderate form), which is associated with exposure to hay dust and mold spores, has certain similarities to human asthma, and continues to represent a therapeutic problem. Immunomodulatory CpG-ODN, bound to gelatin nanoparticles as a drug delivery system, were successfully administered by inhalation to severe equine asthmatic patients in several studies. It was possible to demonstrate a significant, sustained, and allergen-independent one-to-eight-week improvement in key clinical parameters: the arterial partial pressure of oxygen, the quantity and viscosity of tracheal mucus, and neutrophilic inflammatory cells in the respiratory tracts of the severe equine asthmatic subjects. At the immunological level, an upregulation of the regulatory antiallergic and anti-inflammatory cytokine IL-10 as well as a downregulation of the proallergic IL-4 and proinflammatory IFN-γ in the respiratory tracts of the severe equine asthmatic patients were identified in the treatment groups. CD4⁺ T lymphocytes in the respiratory tracts of the asthmatic horses were demonstrated to downregulate the mRNA expression of Tbet and IL-8. Concentrations of matrix metalloproteinase-2 and -9 and tissue inhibitors of metalloproteinase-2 were significantly decreased directly after the treatment as well as six weeks post-treatment. This innovative therapeutic concept thus opens new perspectives in the treatment of severe equine asthma and possibly also that of human asthma.

Comprehensive Flow Cytometric Characterization of Bronchoalveolar Lavage Cells Indicates Comparable Phenotypes Between Asthmatic and Healthy Horses But Functional Lymphocyte Differences

Equine asthma (EA) is a highly relevant disease, estimated to affect up to 20% of all horses, and compares to human asthma. The pathogenesis of EA is most likely immune-mediated, yet incompletely understood. To study the immune response in the affected lower airways, mixed leukocytes were acquired through bronchoalveolar lavage (BAL) and the cell populations were analyzed on a single-cell basis by flow cytometry (FC). Samples of 38 horses grouped as respiratory healthy or affected by mild to moderate (mEA) or severe EA (sEA) according to their history, clinical signs, and BAL cytology were analyzed. Using FC, BAL cells and PBMC were comprehensively characterized by cell surface markers ex vivo. An increased percentage of DH24A⁺ polymorphonuclear cells, and decreased percentages of CD14⁺ macrophages were detected in BAL from horses with sEA compared to healthy horses or horses with mEA, while lymphocyte proportions were similar between all groups. Independently of EA, macrophages in BAL were CD14⁺CD16⁺, which contrasts the majority of CD14⁺CD16^- classical monocytes in PBMC. Percentages of CD16-expressing BAL macrophages were reduced in BAL from horses with sEA compared to healthy horses. While PBMC lymphocytes predominantly contain CD4⁺ T cells, B cells and few CD8⁺ T cells, BAL lymphocytes comprised mainly CD8⁺ T cells, fewer CD4⁺ T cells and hardly any B cells. These lymphocyte subsets’ distributions were similar between all groups. After PMA/ionomycin stimulation in vitro, lymphocyte activation (CD154 and T helper cell cytokine expression) was analyzed in BAL cells of 26 of the horses and group differences were observed (p=0.01–0.11). Compared to healthy horses’ BAL, CD154⁺ lymphocytes from horses with mEA, and CD4⁺IL-17A⁺ lymphocytes from horses with sEA were increased in frequency. Activated CD4⁺ T helper cells were more frequent in asthmatics’ (mEA, sEA) compared to healthy horses’ PBMC lymphocytes. In summary, FC analysis of BAL cells identified increased polymorphonuclear cells frequencies in sEA as established, while macrophage percentages were mildly reduced, and lymphocyte populations remained unaffected by EA. Cytokine production differences of BAL lymphocytes from horses with sEA compared to healthy horses’ cells point towards a functional difference, namely increased local type 3 responses in sEA.

Inter-species cell detection - datasets on pulmonary hemosiderophages in equine, human and feline specimens

Pulmonary hemorrhage (P-Hem) occurs among multiple species and can have various causes. Cytology of bronchoalveolar lavage fluid (BALF) using a 5-tier scoring system of alveolar macrophages based on their hemosiderin content is considered the most sensitive diagnostic method. We introduce a novel, fully annotated multi-species P-Hem dataset, which consists of 74 cytology whole slide images (WSIs) with equine, feline and human samples. To create this high-quality and high-quantity dataset, we developed an annotation pipeline combining human expertise with deep learning and data visualisation techniques. We applied a deep learning-based object detection approach trained on 17 expertly annotated equine WSIs, to the remaining 39 equine, 12 human and 7 feline WSIs. The resulting annotations were semi-automatically screened for errors on multiple types of specialised annotation maps and finally reviewed by a trained pathologist. Our dataset contains a total of 297,383 hemosiderophages classified into five grades. It is one of the largest publicly available WSIs datasets with respect to the number of annotations, the scanned area and the number of species covered.

Muscarinic receptor antagonists and airway inflammation: A systematic review on pharmacological models

Airway inflammation is crucial in the pathogenesis of many respiratory diseases, including chronic obstructive pulmonary disease (COPD) and asthma. Current evidence supports the beneficial impact of muscarinic receptor antagonists against airway inflammation from bench-to-bedside. Considering the numerous sampling approaches and the ethical implications required to study inflammation in vivo in patients, the use of pre-clinical models is inevitable. Starting from our recently published systematic review concerning the impact of muscarinic antagonists, we have systematically assessed the current pharmacological models of airway inflammation and provided an overview on the advances in in vitro and ex vivo approaches. The purpose of in vitro models is to recapitulate selected pathophysiological parameters or processes that are crucial to the development of new drugs within a controlled environment. Nevertheless, immortalized cell lines or primary airway cells present major limitations, including the inability to fully replicate the conditions of the corresponding cell types within a whole organism.

Induced animal models are extensively used in research in the attempt to replicate a respiratory condition reflective of a human pathological state, although considering animal models with spontaneously occurring respiratory diseases may be more appropriate since most of the clinical features are accompanied by lung pathology resembling that of the human condition.

In recent years, three-dimensional organoids have become an alternative to animal experiments, also because animal models are unable to fully mimic the complexity of human pulmonary diseases. Ex vivo studies performed on human isolated airways have a superior translational value compared to in vitro and animal models, as they retain the morphology and the microenvironment of the lung in vivo.

In the foreseeable future, greater effort should be undertaken to rely on more physiologically relevant models, that provide translational value into clinic and have a direct impact on patient outcomes.

CD154 Expression Indicates T Cell Activation Following Tetanus Toxoid Vaccination of Horses

Despite the relevance of adaptive immunity against equine pathogens antigen-specific T cell responses of horses are not well characterized and the lack of insight into T cell responses hampers the understanding of the pathogeneses of important diseases. In this study we used tetanus toxoid (TT) as a well-defined antigen to characterize antigen-reactive T cells. Six healthy adult horses received a routine booster against tetanus with an immune stimulating complex (ISCOM)-based vaccine and were followed for 28 days. TT-specific serum antibodies were quantified by ELISA and increased in all horses by day 7 after vaccination. CD154 is an established indicator of antigen-reactive T helper cells in other species, but has not been characterized in horses. CD154 detection in equine PBMC by an anti-human CD154 antibody (clone 5C8) was confirmed by Western blots and then applied for flow cytometry. As a common indicator of equine T cell activation, cytokine induction was studied in parallel. T cells were analyzed by multicolor flow cytometry of PBMC after re-stimulation with TT in vitro. Reactive T helper (Th) cells were characterized by increased frequencies of CD4⁺CD154⁺ lymphocytes in in vitro TT-re-stimulated PBMC on day 14 after vaccination of the horses compared to pre-vaccination. The majority of all CD154⁺ cells after TT re-stimulation were CD4⁺ Th cells, but CD154 was also induced on CD4^- cells albeit in lower frequencies. CD154⁺CD4⁺ Th cells were enriched in cytokine-expressing cells compared to CD154^-CD4⁺ Th cells. Similar to the CD4⁺CD154⁺ frequencies, CD4⁺IL-4⁺, CD4⁺IFN-γ⁺ and CD4⁺TNF-α⁺ were increased after vaccination, but IL-4⁺ increased later than IFN-γ⁺ and CD4⁺TNF-α⁺, which already exceeded pre-vaccination frequencies on day 7. CD4⁺CD154⁺ frequencies correlated positively with those of CD4⁺IL-4⁺ (Th2) on day 14, and negatively with CD4⁺IFN-γ⁺ induction on day 7, but did not correlate with CD4⁺TNF-α⁺ frequencies or TT-specific antibody concentrations. CD154 appears to be a useful marker of antigen-reactive equine Th cells in combination with cytokine expression. The T cell analyses established here with TT can be applied to other antigens relevant for infections or allergies of horses and in horse models for translational research.

Giant Multinucleated Cells Are Associated with Mastocytic Inflammatory Signature Equine Asthma

Equine asthma is currently diagnosed by the presence of increased neutrophil (>5%), mast cell (>2%), and/or eosinophil (>1%) differential cell count. Macrophages are normal resident cells within the alveoli. Their presence in BALF is considered normal, but the clinical implication of the presence of activated or fused macrophages (giant multinucleated cells, GMC) is currently overlooked. We aimed to assess the prevalence, cytological determinants, and clinical significance of increased GMC counts in BALF of 34 asthmatic horses compared to 10 controls. Counts were performed on 15 randomly selected high magnification fields per cytospin slide (40×), and expressed as GMC:single macrophage (GMC:M) ratio. Regression models were used for statistical analysis. GMC was frequently observed in both asthmatic and control horses, with an increased prevalence of equine asthma (p = 0.01). GMC:M ratio was significantly higher in severe vs. mild to moderate equine asthmatic and control horses. In asthmatic horses, an increased GMC:M ratio was significantly associated with BALF mastocytosis (p = 0.01), once adjusting for age and the presence and severity of clinical signs of the horses. Tachypnea was the only clinical sign that tended to be positively associated with GMC:M ratio after adjustment (p = 0.08). In conclusion, our data suggest that a relationship might exist between molecular mechanisms regulating GMC formation and mast cell recruitment in the equine lung. The same mechanisms could lead to tachypnea even in the absence of respiratory effort at rest. We suggest including GMC count in the basic cytological assessment of BALF samples to gain more insights into their role in equine asthma.

The Immune Mechanisms of Severe Equine Asthma-Current Understanding and What Is Missing

Severe equine asthma is a chronic respiratory disease of adult horses, occurring when genetically susceptible individuals are exposed to environmental aeroallergens. This results in airway inflammation, mucus accumulation and bronchial constriction. Although several studies aimed at evaluating the genetic and immune pathways associated with the disease, the results reported are inconsistent. Furthermore, the complexity and heterogeneity of this disease bears great similarity to what is described for human asthma. Currently available studies identified two chromosome regions (ECA13 and ECA15) and several genes associated with the disease. The inflammatory response appears to be mediated by T helper cells (Th1, Th2, Th17) and neutrophilic inflammation significantly contributes to the persistence of airway inflammatory status. This review evaluates the reported findings pertaining to the genetical and immunological background of severe equine asthma and reflects on their implications in the pathophysiology of the disease whilst discussing further areas of research interest aiming at advancing treatment and prognosis of affected individuals.

Effects of azithromycin on bronchial remodeling in the natural model of severe neutrophilic asthma in horses

Steroid resistance in asthma has been associated with neutrophilic inflammation and severe manifestations of the disease. Macrolide add-on therapy can improve the quality of life and the exacerbation rate in refractory cases, possibly with greater effectiveness in neutrophilic phenotypes. The mechanisms leading to these beneficial effects are incompletely understood and whether macrolides potentiate the modulation of bronchial remodeling induced by inhaled corticosteroids (ICS) is unknown. The objective of this study was to determine if adding azithromycin to ICS leads to further improvement of lung function, airway inflammation and bronchial remodeling in severe asthma. The combination of azithromycin (10 mg/kg q48h PO) and inhaled fluticasone (2500 µg q12h) was compared to the sole administration of fluticasone for five months in a randomized blind trial where the lung function, airway inflammation and bronchial remodeling (histomorphometry of central and peripheral airways and endobronchial ultrasound) of horses with severe neutrophilic asthma were assessed. Although the proportional reduction of airway neutrophilia was significantly larger in the group receiving azithromycin, the lung function and the peripheral and central airway smooth muscle mass decreased similarly in both groups. Despite a better control of airway neutrophilia, azithromycin did not potentiate the other clinical effects of fluticasone.

Training associated alterations in equine respiratory immunity using a multiomics comparative approach

Neutrophilic airway inflammation is highly prevalent in racehorses in training, with the term mild to moderate equine asthma (MMEA) being applied to the majority of such cases. Our proposed study is largely derived from the strong association between MMEA in racehorses and their entry into a race training program. The objectives of this study are to characterise the effect of training on the local pulmonary immune system by defining the gene and protein expression of tracheal wash (TW) derived samples from Thoroughbred racehorses prior to and following commencement of race training. Multiomics analysis detected 2138 differentially expressed genes and 260 proteins during the training period. Gene and protein sets were enriched for biological processes related to acute phase response, oxidative stress, haemopoietic processes, as well as to immune response and inflammation. This study demonstrated TW samples to represent a rich source of airway cells, protein and RNA to study airway immunity in the horse and highlighted the benefits of a multiomics methodological approach to studying the dynamics of equine airway immunity. Findings likely reflect the known associations between race-training and both airway inflammation and bleeding, offering further insight into the potential mechanisms which underpin training associated airway inflammation.

MicroRNAs: Potential biomarkers for reproduction, diagnosis, prognosis, and therapeutic in domestic animals

MicroRNA (miRNAs) are small non-coding RNA molecules involved in a wide range of biological processes through the post-transcriptional regulation of gene expression. Most studies evaluated microRNA expression in human, and despite fewer studies in veterinary medicine, this topic is one of the most exciting areas of modern veterinary medicine. miRNAs showed to be part of the pathogenesis of diseases and reproduction physiology in animals, making them biomarkers candidates. This review provides an overview of the current knowledge regarding miRNAs' role in reproduction and animal diseases, diagnostic and therapy.

Asthmatic Bronchial Matrices Determine the Gene Expression and Behavior of Smooth Muscle Cells in a 3D Culture Model

Asthma is associated with increased deposition and altered phenotype of airway smooth muscle (ASM) cells. However, little is known about the processes responsible for these changes. It has been suggested that alterations of the extracellular matrix (ECM) contribute to the remodeling of ASM cells in asthma. Three-dimensional matrices allow the in vitro study of complex cellular responses to different stimuli in a close-to-natural environment. Thus, we investigated the ultrastructural and genic variations of ASM cells cultured on acellular asthmatic and control bronchial matrices. We studied horses, as they spontaneously develop a human asthma-like condition (heaves) with similarities to chronic pulmonary changes observed in human asthma. Primary bronchial ASM cells from asthmatic (n = 3) and control (n = 3) horses were cultured on decellularized bronchi from control (n = 3) and asthmatic (n = 3) horses. Each cell lineage was used to recellularize six different bronchi for 41 days. Histomorphometry on HEPS-stained-recellularized matrices revealed an increased ASM cell number in the control cell/control matrix (p = 0.02) and asthmatic cell/control matrix group (p = 0.04) compared with the asthmatic cell/asthmatic matrix group. Scan electron microscopy revealed a cell invasion of the ECM. While ASM cells showed high adhesion and proliferation processes on the control ECM, the presence of senescent cells and cellular debris in the asthmatic ECM with control or asthmatic ASM cells suggested cell death. When comparing asthmatic with control cell/matrix combinations by targeted next generation sequencing, only AGC1 (p = 0.04), MYO10 (p = 0.009), JAM3 (p = 0.02), and TAGLN (p = 0.001) were differentially expressed out of a 70-gene pool previously associated with smooth muscle remodeling. To our knowledge, this is the first attempt to evaluate the effects of asthmatic ECM on an ASM cell phenotype using a biological bronchial matrix. Our results indicate that bronchial ECM health status contributes to ASM cell gene expression and, possibly, its survival.

Some Genetic and Environmental Effects on Equine Asthma in Polish Konik Horses

Simple Summary

Equine Asthma (EA) is a blanket term covering inflammatory diseases of the lower airways in horses. It includes mild-to-moderate equine asthma, which affects horses of any age, and severe equine asthma, which is typically seen in horses older than 7 years of. Relationships of the disease’s occurrence with sex or breed have been proven. However, some authors consider genetic background a predisposing factor, due to the fact that in some bloodlines a clinical form of asthma is more frequently observed. This indicates serious breeding and economic consequences. This study aimed to identify the factors affecting predisposition to severe equine asthma in the population of Polish Konik horses and some environmental and inbreeding effects on the disease. Generally, in the observed population, EA is negligibly affected by the factors analysed. Individual inbreeding effects on asthma were not confirmed by various statistical approaches, but significant maternal inbreeding effects were observed. These results are very important from the perspective of the currently implemented genetic resource conservation programme.

Abstract

Current knowledge of the genetic and environmental backgrounds of equine asthma seems to be insufficient, especially for primitive horse breeds. The main objectives of this study were to estimate the effects of sex, birth period, stud, parentage line and inbreeding on asthma morbidity in Polish Konik horses. Records of 274 horses (housed in two studs) were analysed. These animals were allocated to maternal and paternal lines. Individual inbreeding coefficients were extracted from the additive relationship matrix. Horses underwent diagnosis based on observation of the basic symptoms (high frequency of coughing and excessive nasal discharge). Subsequently, some horses (28 individuals) were clinically examined to confirm the earlier observations. Generally, no significant effects of parentage line on heaves morbidity were identified by the use of logistic regression, although the Pearson’s chi-squared test had shown that individuals of some maternal and paternal lines had a predisposition to severe equine asthma. It was concluded that the individual inbreeding level is not associated with the incidence of EA, but a significant effect of the maternal inbreeding coefficient may be observed. It was also found that there is some variability in the incidence of this disease between studs.

Intradermal Testing Results in Horses Affected by Mild-Moderate and Severe Equine Asthma

Simple Summary

Equine asthma is a respiratory syndrome sharing several similarities with human asthma and represents the most common cause of chronic coughing in horses. Based on the severity and recurrence of the conditions, it is classified as mild-moderate or severe equine asthma. Although a precise pathogenetic mechanism has not yet been identified, it is generally agreed that environmental allergens behave as triggers of a hypersensitivity response (HR), culminating in asthmatic exacerbations. In human medicine, the skin prick test is considered the gold standard of allergy testing; similarly, in equine medicine, intradermal testing is used to identify hypersensitivities to specific allergens. The present study describes and compares the results of intradermal testing in horses affected by either mild-moderate or severe equine asthma to evaluate the responsiveness of asthmatic horses and to identify the most frequently involved allergens. Type-I HR was shown to play a major role in the pathogenesis of severe equine asthma, while type-IV HR seems to be involved mostly in milder forms. Insects represented the antigens inducing the most frequent and strongest reactions among asthmatic horses, followed by Dermatophagoides spp. and dog epithelium; these allergens should therefore be considered for avoidance strategies and the future development of desensitizing allergen-specific immunotherapy.

Abstract

Equine asthma is an inflammatory respiratory disorder, classified as mild-moderate (MEA) and severe (SEA). SEA is characterized by recurrent exacerbations, consisting of dyspnea, coughing and exercise intolerance; MEA causes poor performance, occasional cough and mucus hypersecretion. Although a precise pathogenesis is not completely understood, allergic mechanisms are considered an important pathophysiological feature of equine asthma. In equine medicine, intradermal testing (IDT) is effective in identifying hypersensitivity to specific allergens. However, to date, the studies about IDT in asthmatic horses obtained contradictory results. This study aims to evaluate IDT responses in MEA and SEA horses and to identify the most significant allergens. Thirty-eight asthmatic horses were enrolled and underwent IDT using 50 allergens; reactions were evaluated at 30 min, 4, 24 and 48 h and were assigned a score from 0 to 4. In SEA horses, the most frequent and strongest reactions were observed at 30 min and 4 h, suggesting the involvement of type I hypersensitivity; in MEA horses, also type IV hypersensitivity seemed to play a major role. Insects, Dermatophagoides spp. and dog epithelium induced in MEA and SEA horses the most significant hypersensitivity responses and could therefore be considered as the main allergenic antigens in our geographic area.

Application across species of a one health approach to liquid sample handling for respiratory based -omics analysis

Airway inflammation is highly prevalent in horses, with the majority of non-infectious cases being defined as equine asthma. Currently, cytological analysis of airway derived samples is the principal method of assessing lower airway inflammation. Samples can be obtained by tracheal wash (TW) or by lavage of the lower respiratory tract (bronchoalveolar lavage (BAL) fluid; BALF). Although BALF cytology carries significant diagnostic advantages over TW cytology for the diagnosis of equine asthma, sample acquisition is invasive, making it prohibitive for routine and sequential screening of airway health. However, recent technological advances in sample collection and processing have made it possible to determine whether a wider range of analyses might be applied to TW samples. Considering that TW samples are relatively simple to collect, minimally invasive and readily available in the horse, it was considered appropriate to investigate whether, equine tracheal secretions represent a rich source of cells and both transcriptomic and proteomic data. Similar approaches have already been applied to a comparable sample set in humans; namely, induced sputum. Sputum represents a readily available source of airway biofluids enriched in proteins, changes in the expression of which may reveal novel mechanisms in the pathogenesis of respiratory diseases, such as asthma and chronic obstructive pulmonary disease. The aim of this study was to establish a robust protocol to isolate macrophages, protein and RNA for molecular characterization of TW samples and demonstrate the applicability of sample handling to rodent and human pediatric bronchoalveolar lavage fluid isolates. TW samples provided a good quality and yield of both RNA and protein for downstream transcriptomic/proteomic analyses. The sample handling methodologies were successfully applicable to BALF for rodent and human research. TW samples represent a rich source of airway cells, and molecular analysis to facilitate and study airway inflammation, based on both transcriptomic and proteomic analysis. This study provides a necessary methodological platform for future transcriptomic and/or proteomic studies on equine lower respiratory tract secretions and BALF samples from humans and mice.

Bronchial angiogenesis in horses with severe asthma and its response to corticosteroids

Background

Severe asthma in horses is characterized by structural changes that thicken the lower airway wall, a change that is only partially reversible by current treatments. Increased vascularization contributes to the thickening of the bronchial wall in humans with asthma and is considered a potential new therapeutic target.

Objective

To determine the presence of angiogenesis in the bronchi of severely asthmatic horses, and if present, to evaluate its reversibility by treatment with corticosteroids.

Animals

Study 1: Bronchial samples from asthmatic horses in exacerbation (7), in remission (7), and aged‐matched healthy horses. Study 2: Endobronchial biopsy samples from asthmatic horses in exacerbation (6) and healthy horses (6) before and after treatment with dexamethasone.

Methods

Blinded, randomized controlled study. Immunohistochemistry was performed using collagen IV as a marker for vascular basement membranes. Number of vessels, vascular area, and mean vessel size in the bronchial lamina propria were measured by histomorphometry. Reversibility of vascular changes in Study 2 was assessed after 2 weeks of treatment with dexamethasone.

Results

The number of vessels and vascular area were increased in the airway walls of asthmatic horses in exacerbation (P = .01 and P = .02, respectively) and in remission (P = .02 and P = .04, respectively) when compared to controls. In Study 2, the differences observed between groups disappeared after 2 weeks of treatment with corticosteroids because of the increased number of vessels in healthy horses.

Conclusions and Clinical Importance

Angiogenesis contributes to thickening of the airway wall in asthmatic horses and was not reversed by a 2‐week treatment with corticosteroids.

Immunohistochemical Expression of Neurokinin-A and Interleukin-8 in the Bronchial Epithelium of Horses with Severe Equine Asthma Syndrome during Asymptomatic, Exacerbation, and Remission Phase

Severe equine asthma (EA) syndrome is a chronic obstructive disease characterized by exaggerated contraction, inflammation, and structural alteration of the airways in adult horses, when exposed to airborne molds and particulate material. However, little is known about the relationship between the degree and type of inflammation on one hand, and the severity of the disease and the response to treatment on the other. Furthermore, to date, very few studies evaluate the diagnostic value of histology and immunohistochemical features of endoscopic biopsies on subjects with severe equine asthma. To investigate the expression of two inflammatory markers (NKA and IL-8) before, during, and after the exacerbation of severe EA, a histological and immunohistochemical study was carried out on a series of biopsy samples collected by bronchoscopy from six EA-affected horses subjected to process exacerbation through environmental stimuli and then to pharmacological treatment. The application of a histological biopsy scoring system revealed a significant difference between control cases and the EA-affected horses in all experimental phases (asymptomatic, early exacerbation phase, late exacerbation phase, and remission phase). For immunohistochemistry (IHC), only the intensity of NKA positivity increases significantly between control horses and the EA horses at late exacerbation and remission phases. In EA-affected horses, a difference was detected by comparing histology between asymptomatic and remission phase, meanwhile, NKA and IL-8 showed no differences between the experimental phases. Based on these results we can assert that: (1) The endoscopic biopsies generate reliable and homogeneous samples in the entire bronchial tree; (2) the clinical improvement associated with treatment is characterized by a significant worsening of the histological findings; and (3) the NKA immunopositivity seems to increase significantly rather than decrease, as one would have expected, after pharmacological treatment. Further studies are necessary both to implement the number of samples and to use other markers of inflammation to characterize the potential role of cytokines in the diagnosis and therapeutic approach of severe equine asthma.

Nicoletella semolina in the airways of healthy horses and horses with severe asthma

Background

Nicoletella semolina was identified in the airways of horses and its low prevalence could be because of its difficult differentiation from other Pasteurellaceae.

Objectives

To develop a molecular method for the identification of N. semolina and to evaluate its prevalence in the mouth and the airways of healthy and severe asthmatic horses.

Animals

Six healthy and 6 severely asthmatic horses in phase I, 10 severely asthmatic horses in phase II, and 10 healthy horses in phase III.

Methods

Cohort (phases I and II) and cross‐sectional (phase III) studies. Quantitative polymerase chain reaction primers targeting the sodA gene were optimized. N. semolina was quantified in oral and nasal washes and in bronchoalveolar lavage fluid (BALF; phase I, sampled twice), in nasal washes and BALF (phase II, sampled twice), and in nasal washes (phase III).

Results

N. semolina was found in the nose of 5, 10, and 9 horses in phases I, II, and III, respectively (first sampling for phases I and II). Six BALF from 5 different horses were positive for N. semolina in phase II. In phase I, there was no significant difference in the nasal loads of healthy horses (median (range): 2.04 × 10⁴ copies/mL (0‐2.44 × 10⁵)) and asthmatic horses in exacerbation (3.75 × 10² (0‐4.84 × 10⁶); Wilcoxon's rank sum test, P = .57).

Conclusions and Clinical Importance

N. semolina is commonly found in the airways of horses. The potential pathogenicity of N. semolina remains to be elucidated, but the molecular technique we developed will facilitate future studies.

Case-Control Study of Risk Factors for Equine Asthma in Texas

Equine asthma is a common condition in horses, for which few host-related risk factors have been identified. The objective of this study was to identify host-related risk factors for the development of equine asthma. A retrospective, case-control study was performed, utilizing horses presented to the Texas A&M University, Veterinary Medical Teaching Hospital from January 2014 December 2018. Incident cases of mild to severe equine asthma (n = 37), diagnosed clinically with cytologic support of disease were examined. For each case, two control populations were identified, including one temporal control (n = 37) and one age-matched control (n = 37). Data collected included signalment, dietary and stable management, prior medical history, metabolic status, physical examination findings, and results of cytologic evaluation via bronchoalvelolar lavage or tracheal wash. Conditional logistic regression was used to compare data on equine asthma cases with data from each set of controls. Results indicated that obesity (Body Condition Score ≥ 7) was the only statistically significant risk factor for equine asthma in this population of horses. These results may aid in identification of targets for management, prevention, and further investigation into the pathogenesis of equine asthma. Early identification and intervention of horses at risk of lower airway disease could ameliorate the impact of disease.

The Dynamics of Circulating Immune Complexes in Horses with Severe Equine Asthma

Simple Summary

Equine asthma syndrome is a cost-consuming equine respiratory disease of the lower airways in horses. Non-invasive biomarkers from blood or urine are sought. The aim of this study was to assess the circulating immune complexes (CICs) during the exacerbation and remission of an asthma episode—with and without additional treatment and the potential usefulness of CIC levels in the diagnosis, monitoring, and treatment progression. The control group, asthma group, and treated asthma group each contained six horses. The horses were kept in a dusty environment for seven days and then moved to an asthma-friendly environment for over three weeks (the treated group received injections of glucocorticoids). Blood was collected at baseline and on the 1st, 2nd, 3rd, 7th, 14th and 30th days. CICs measured in the time points did not show statistical differences. When CICs were analysed within the groups, there was a significant decrease in CIC in the treated group and a significant increase in CIC in the non-treated group on day 30. CIC did not support the diagnosis procedure of equine asthma syndrome, although it may help in monitoring patients with and without treatment. To the best of the authors’ knowledge, this is the first study to analyse the dynamics of CIC in equine asthma patients during an environmental challenge, remission, and treatment.

Abstract

Non-invasive diagnostic biomarkers of equine asthma syndrome (EAS) from blood or urine are sought. The aim of this study was to assess the absorbance of circulating immune complexes (CICs) during the exacerbation, remission, and treatment of an asthma episode and assess the potential usefulness of CIC levels in the diagnosis and monitoring of the disease. The control group, asthma group, and treated asthma group each contained six horses. Following an initial examination and group classification, the horses were kept in a dusty environment for seven days and then moved to an asthma-friendly environment for three weeks (the treated group received injections of glucocorticoids). Blood was collected at baseline and on the 1st, 2nd, 3rd, 7th, 14th and 30th days. CIC was measured using the modified Haskova method. The time points did not show significant statistical differences. There was a significant decrease in CIC in the treated group, and a significant increase in CIC in the non-treated group on day 30. CIC did not support the EAS diagnosis, although it may help in monitoring patients. To the best of the authors’ knowledge, this is the first study to analyse the dynamics of CIC during environmental challenge, remission, and treatment.

The Usefulness of Mesenchymal Stem Cells beyond the Musculoskeletal System in Horses

Simple Summary

The main target of mesenchymal stem cell therapy in horses has long been the locomotor system, because these athletic animals commonly suffer from tendon and joint lesions. Originally, mesenchymal stem cells were thought to act by just differentiating into the cells of the injured tissue. However, these cells are also able to regulate and stimulate the body’s own repair mechanisms, opening the door to many applications in inflammatory and immune-mediated disorders in both animals and humans. In horses, beyond their traditional application in the musculoskeletal system, these cells have been studied for ophthalmologic pathologies such as corneal ulcers or immune-mediated processes, and for reproductive disorders such as endometritis/endometrosis. Their potential has been explored for equine pathologies very similar to those affecting people, such as asthma, metabolic syndrome, aberrant wound healing, or endotoxemia, as well as for equine-specific pathologies such as laminitis. Current evidence is still preliminary, and further research is needed to clarify different aspects, although research performed so far shows the promising potential of mesenchymal stem cells to treat a wide variety of equine pathologies, some of which are analogous to human disorders. Therefore, advancements in this path will be beneficial for both animals and people.

Abstract

The differentiation ability of mesenchymal stem cells (MSCs) initially raised interest for treating musculoskeletal injuries in horses, but MSC paracrine activity has widened their scope for inflammatory and immune-mediated pathologies in both equine and human medicine. Furthermore, the similar etiopathogenesis of some diseases in both species has advanced the concept of “One Medicine, One Health”. This article reviews the current knowledge on the use of MSCs for equine pathologies beyond the locomotor system, highlighting the value of the horse as translational model. Ophthalmologic and reproductive disorders are among the most studied for MSC application. Equine asthma, equine metabolic syndrome, and endotoxemia have been less explored but offer an interesting scenario for human translation. The use of MSCs in wounds also provides a potential model for humans because of the healing particularities in both species. High-burden equine-specific pathologies such as laminitis have been suggested to benefit from MSC-therapy, and MSC application in challenging disorders such as neurologic conditions has been proposed. The available data are preliminary, however, and require further development to translate results into the clinic. Nevertheless, current evidence indicates a significant potential of equine MSCs to enlarge their range of application, with particular interest in pathologies analogous to human conditions.

Inhaled ciclesonide is efficacious and well tolerated in the treatment of severe equine asthma in a large prospective European clinical trial

Background

Ciclesonide is a glucocorticoid prodrug, already registered for human use. Due to its mode of action and inhaled route of administration, it was considered an appropriate treatment option for horses with severe equine asthma. Although the efficacy of inhaled ciclesonide has been demonstrated in horses with asthma exacerbations under controlled mouldy hay challenge conditions, it has not yet been reported under field conditions.

Objectives

To assess the effectiveness and safety of inhaled ciclesonide for the treatment of severe equine asthma.

Study design

Prospective, multicentre, placebo‐controlled, randomised, double‐blinded study.

Methods

Two‐hundred and twenty‐four client‐owned horses with severe equine asthma were randomised (1:1 ratio) to receive either ciclesonide inhalation (343 µg/actuation) solution or placebo (0 µg/actuation). Treatments (placebo or ciclesonide) were administered with a nonpressurised Soft Mist™ inhaler specifically developed for horses (Aservo^® EquiHaler^®) at doses of 8 actuations twice daily for the first 5 days and 12 actuations once daily for the following 5 days. Primary outcome was a success/failure analysis with the a priori definition of treatment success as a 30% or greater reduction in weighted clinical score (WCS) between Day 0 and Day 10 (±1).

Results

The treatment success rate (as defined above) in ciclesonide‐treated horses was 73.4% (80/109) after 10 (±1) days of treatment, being significantly higher than in the placebo group with 43.2% (48/111; P < 0.0001). Few systemic and local adverse events of ciclesonide were observed.

Main limitations

The severity of clinical signs of severe equine asthma varies over time; despite the prohibition of environmental management changes during the study, a placebo effect was also identified. This potentially contributed, in part, to the clinical improvement observed in the ciclesonide‐treated group.

Conclusions

Ciclesonide inhalation solution administered by the Aservo^® EquiHaler^® effectively reduced severity of clinical signs in a majority of horses with severe equine asthma and was well tolerated.

Severe asthma is associated with a remodeling of the pulmonary arteries in horses

Pulmonary hypertension and cor pulmonale are complications of severe equine asthma, as a consequence of pulmonary hypoxic vasoconstriction. However, as pulmonary hypertension is only partially reversible by oxygen administration, other etiological factors are likely involved. In human chronic obstructive pulmonary disease, pulmonary artery remodeling contributes to the development of pulmonary hypertension. In rodent models, pulmonary vascular remodeling is present as a consequence of allergic airway inflammation. The present study investigated the presence of remodeling of the pulmonary arteries in severe equine asthma, its distribution throughout the lungs, and its reversibility following long-term antigen avoidance strategies and inhaled corticosteroid administration. Using histomorphometry, the total wall area of pulmonary arteries from different regions of the lungs of asthmatic horses and controls was measured. The smooth muscle mass of pulmonary arteries was also estimated on lung sections stained for α-smooth muscle actin. Reversibility of vascular changes in asthmatic horses was assessed after 1 year of antigen avoidance alone or treatment with inhaled fluticasone. Pulmonary arteries showed increased wall area in apical and caudodorsal lung regions of asthmatic horses in both exacerbation and remission. The pulmonary arteries smooth muscle mass was similarly increased. Both treatments reversed the increase in wall area. However, a trend for normalization of the vascular smooth muscle mass was observed only after treatment with antigen avoidance, but not with fluticasone. In conclusion, severe equine asthma is associated with remodeling of the pulmonary arteries consisting in an increased smooth muscle mass. The resulting narrowing of the artery lumen could enhance hypoxic vasoconstriction, contributing to pulmonary hypertension. In our study population, the antigen avoidance strategy appeared more promising than inhaled corticosteroids in controlling vascular remodeling. However, further studies are needed to support the reversibility of vascular smooth muscle mass remodeling after asthma treatment.

Involvement of hemostasis in pathophysiology of RAO in horses

Recurrent Airway Obstruction (RAO), also called severe asthma or heaves, is a chronic disease in adult horses caused by aeroallergens from straw or hay. Disturbances in hemostasis (intensified coagulation and depressed fibrinolysis) are considered one of the prominent reasons of inflammatory process, injury and dysfunction of the lungs. The aim of the study was to evaluate chosen parameters of hemostasis in horses with active form of RAO. Ten RAO-horses (group R) and ten healthy horses (group C) were exposed to straw and hay allergen challenge. The prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT), fibrinogen concentration (Fb), stabilized fibrin degradation product (d-dimer), antithrombin (AT), protein C and coagulation factors II through XII were assessed in plasma obtained from blood of all the horses. Exposure to aeroallergens resulted in prolongation of aPTT in both groups of animals; it was evident in the group R and moderate in the group C. There were no differences in PT and TT. Concentrations of fibrinogen and d-dimer and activity of protein C in both groups were increased but lay within or near to reference values. The activity of AT was depressed in RAO-horses. All exposed horses showed increased activity of coagulation factors II, VIII and X but they had no changes in activity of factor V. Factors VII and XII displayed a reduction in activity. The decrease in factor IX activity was noted in the group C only. Various changes were observed in activity of factor XI; in horses with RAO it was elevated but in healthy horses it was declined. The changes of the parameters tested in RAO-horses indicate the involvement of coagulation and fibrinolysis which apparently remained under control of efficient and active mechanisms of general hemostasis.

Metabolomics analysis of bronchoalveolar lavage fluid samples in horses with naturally-occurring asthma and experimentally-induced airway inflammation

The present work characterized the metabolomic profile of bronchoalveolar lavage fluid (BALF) in healthy horses, experimentally-induced airway inflammation by lipopolysaccharide (LPS) nebulization, and naturally-occurring asthma (n = 3 in each group). All animals underwent clinical and upper airway endoscopic examinations, and bronchoalveolar lavage. BALF supernatant samples were subjected to metabolic analysis based on gas chromatography-mass spectrometry (GC-MS). Overall, 67 peaks were obtained from BALF GC-MS analysis, corresponding to 53 metabolites which were categorized according to chemical class, such as organic acids, fatty acids, nucleosides or their derivatives, amino acids, peptides or their derivatives, carbohydrates, and other compounds. Our results showed that the airway inflammation induction model with LPS produced the same pattern of metabolite changes as in horses with naturally occurring asthma. Metabolic pathway analysis was done by means of Fisher's exact test, for detection of metabolites over-represented in asthma affected-horses and LPS-induced airway inflammation as compared with healthy horses. The most significant altered metabolic pathways were fatty acid biosynthesis, galactose metabolism and citrate cycle. These results suggest that the airway inflammation induction model with LPS is a good study model for asthma-affected horses, due to the similarity of the profile of inflammatory cells (specifically neutrophils) and similar metabolic alterations found in BALF that occur during the inflammatory process of the airways. Further research may increase understanding of metabolomics disturbances and their significance in the pathogenesis of equine asthma.

The equine mononuclear phagocyte system: The relevance of the horse as a model for understanding human innate immunity

The mononuclear phagocyte system (MPS) is a family of cells of related function that includes bone marrow progenitors, blood monocytes and resident tissue macrophages. Macrophages are effector cells in both innate and acquired immunity. They are a major resident cell population in every organ and their numbers increase in response to proinflammatory stimuli. Their function is highly regulated by a wide range of agonists, including lymphokines, cytokines and products of microorganisms. Macrophage biology has been studied most extensively in mice, yet direct comparisons of rodent and human macrophages have revealed many functional differences. In this review, we provide an overview of the equine MPS, describing the variation in the function and phenotype of macrophages depending on their location and the similarities and differences between the rodent, human and equine immune response. We discuss the use of the horse as a large animal model in which to study macrophage biology and pathological processes shared with humans. Finally, following the recent update to the horse genome, facilitating further comparative analysis of regulated gene expression between the species, we highlight the importance of future transcriptomic macrophage studies in the horse, the findings of which may also be applicable to human as well as veterinary research.

An Integrative miRNA-mRNA Expression Analysis Reveals Striking Transcriptomic Similarities between Severe Equine Asthma and Specific Asthma Endotypes in Humans

Severe equine asthma is an incurable obstructive respiratory condition affecting 10–15% of horses in temperate climates. Upon exposure to airborne antigens from hay feeding, affected horses show neutrophilic airway inflammation and bronchoconstriction, leading to increased respiratory effort. The resulting implications range from welfare concerns to economic impacts on equestrian sports and horse breeding. Immunological and pathophysiological characteristics of severe equine asthma show important parallels with allergic and severe neutrophilic human asthma. Our study aimed at investigating regulatory networks underlying the pathophysiology of the disease by profiling miRNA and mRNA expression in lung tissue samples from asthmatic horses compared with healthy controls. We sequenced small RNAs and mRNAs from lungs of seven asthmatic horses in exacerbation, five affected horses in remission, and eight healthy control horses. Our comprehensive differential expression analyses, combined with the miRNA–mRNA negative correlation approach, revealed a strong similarity on the transcriptomic level between severe equine asthma and severe neutrophilic asthma in humans, potentially through affecting Th17 cell differentiation. This study also showed that several dysregulated miRNAs and mRNAs are involved in airway remodeling. These results present a starting point for a better transcriptomic understanding of severe equine asthma and its similarities to asthma in humans.

Large Animal Models in Regenerative Medicine and Tissue Engineering: To Do or Not to Do

Rapid developments in Regenerative Medicine and Tissue Engineering has witnessed an increasing drive toward clinical translation of breakthrough technologies. However, the progression of promising preclinical data to achieve successful clinical market authorisation remains a bottleneck. One hurdle for progress to the clinic is the transition from small animal research to advanced preclinical studies in large animals to test safety and efficacy of products. Notwithstanding this, to draw meaningful and reliable conclusions from animal experiments it is critical that the species and disease model of choice is relevant to answer the research question as well as the clinical problem. Selecting the most appropriate animal model requires in-depth knowledge of specific species and breeds to ascertain the adequacy of the model and outcome measures that closely mirror the clinical situation. Traditional reductionist approaches in animal experiments, which often do not sufficiently reflect the studied disease, are still the norm and can result in a disconnect in outcomes observed between animal studies and clinical trials. To address these concerns a reconsideration in approach will be required. This should include a stepwise approach using in vitro and ex vivo experiments as well as in silico modeling to minimize the need for in vivo studies for screening and early development studies, followed by large animal models which more closely resemble human disease. Naturally occurring, or spontaneous diseases in large animals remain a largely untapped resource, and given the similarities in pathophysiology to humans they not only allow for studying new treatment strategies but also disease etiology and prevention. Naturally occurring disease models, particularly for longer lived large animal species, allow for studying disorders at an age when the disease is most prevalent. As these diseases are usually also a concern in the chosen veterinary species they would be beneficiaries of newly developed therapies. Improved awareness of the progress in animal models is mutually beneficial for animals, researchers, human and veterinary patients. In this overview we describe advantages and disadvantages of various animal models including domesticated and companion animals used in regenerative medicine and tissue engineering to provide an informed choice of disease-relevant animal models.