Influences of age and sex on leukocytes of healthy horses and their ex vivo cytokine release

Circadian Oscillation of Leukocyte Subpopulations and Inflammatory Cytokines over a 24-H Period in Horses

The objective of the present study was to investigate the influence of daily rhythms on the immune and inflammatory systems in horses, considering white blood cell count (WBCs), leukocyte subpopulations (neutrophils, basophils, eosinophils, lymphocytes, and monocytes), CD4+, and CD8+ lymphocyte populations, interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). Ten Italian Saddle horses (7-12 years old, body weight 480 ± 30 kg) underwent blood sampling every 4 h over a 24-h period. The COSINOR method was used to identify rhythms and their parameters. A one-way analysis of variance (ANOVA) was applied to identify the differences in acrophase and robustness, and a multiple correlation analysis model (Pearson) was used to evaluate the relationships among the investigated parameters. WBCs, leukocyte subpopulations, CD4+, CD8+, IL-1β, IL-6, and TNFα exhibited daily rhythmicity. In particular, white WBCs, lymphocytes, IL-1β, and IL-6 reached their acrophases during the dark phase, while neuthrophils, CD4+, CD8+, and TNFα showed a diurnal acrophase. One-way ANOVA showed a statistical difference in the acrophase among the investigated parameters (p < 0.0001). The Pearson correlation matrix showed positive and negative relationships among the parameters. Circadian rhythms should be taken into consideration with the daily fluctuations in immune and inflammatory biomarkers to develop good management practices and improve welfare in horses.

The effect of dietary camelina, flaxseed, and canola oil supplementation on skin fatty acid profile and immune and inflammatory responses in healthy adult horses

Camelina sativa is an oilseed crop rich in α-linolenic acid (ALA), an n-3 fatty acid (FA), and is resistant to harsh climates and pests. Previously, supplementation with camelina oil (CAM) in horses had no adverse effects on basic health parameters and had comparable skin and coat parameters as both flaxseed oil (FLX) and canola oil (OLA). Further, the plasma FA profile of horses was reflective of their respective treatment oil. The objective of this study was to assess the effects of dietary CAM supplementation on skin FA profile, immune, and inflammatory responses as compared to 2 commonly used oils in the equine industry, OLA and FLX, in healthy adult horses. Twenty-four adult horses, from 2 separate herds, were enrolled in this experiment. The horses underwent a gradual 4-wk fat acclimation period to sunflower oil (approximately 0.28% ALA), then were supplemented with either CAM (approximately 34.9% ALA), OLA (approximately 12.0% ALA), or FLX (56.0% ALA) at an inclusion rate of 0.37 g/kg body weight (BW) per day for an additional 16 wk. Immune and inflammatory responses were assessed by measuring antibody concentrations across time after sensitization to keyhole limpet hemocyanin (KLH) at weeks 10 and 12, and a subsequent delayed-type hypersensitivity (DTH) challenge. Skin biopsy samples were collected at weeks 0, 8, and 16, and FA composition was determined using gas-chromatography. All data were analyzed as a repeated measures ANOVA using PROC GLIMMIX in SAS. Antibody and DTH responses to KLH did not differ among groups (P = 0.262 and 0.813, respectively), and no treatment by time effects were observed (P = 0.764 and P = 0.817, respectively). Most FA in the skin changed in composition across time, with the sum of n-3 FA increasing (P < 0.001) and the sum of n-6 FA and skin n-6:n-3 ratio decreasing over time (P < 0.001 and P < 0.001, respectively). Only dihomo-γ-linolenic acid (P = 0.025) and the sum of n-3 FA (P = 0.031) had treatment-by-week effects. At week 16, the composition of eicosapentaenoic acid in the skin was greater in FLX than OLA, but neither differed from CAM (P = 0.049). These results suggest that ALA supplementation may beneficially impact skin FA profile. However, due to the small differences in n-3 FA and n-6:n-3 ratio among CAM, FLX, and OLA, a comparable skin FA profile, immune, and inflammatory response was observed among treatments at a dose of 0.37 g oil/kg BW. Therefore, CAM may be a suitable alternative to FLX in equine diets for the delivery of ALA.

Morphometric parameters of blood lymphocytes in American mink (Neogale vison) selected for tameness and defensive aggression toward humans

Although there is some evidence to suggest that there is a link between behavior and immune parameters in animals, this issue is still not well understood. In particular, there is a lack of understanding of how specific behaviors affect the size of immune cells. To address this issue, we investigated the relationship between behavior and the morphometric parameters of lymphocytes in American mink (Neogale vison) that have been selectively bred for aggression and tameness toward humans at the Institute of Cytology and Genetics in Novosibirsk, Russia, for 37 years. Minks with high ("-3") and medium ("-2") aggressiveness, moderate ("+ 3") and high tameness ("+ 6"), as well as those not affected by special behavior selection, were compared with each other. We found that aggressive and tame mink significantly differed in lymphocyte size, cytoplasm content and nucleus to cell ratio (NCR). The lymphocytes of tame mink were characterized by larger size, increased cytoplasm content and lower NCR compared to those of aggressive mink and unselected mink. Among the studied parameters, the largest differences were found in the size of lymphocytes between "+ 3" and unselected minks (p = 0.000018) and in the cytoplasm content between "+ 6" and unselected minks (p = 0.000039). Minks with similar behavior ("-3" and "-2", "+ 3" and "+ 6") showed no significant differences. Our data, combined with the strong correlation reported by other researchers between morphological characteristics of lymphocytes and cytokine levels indicates that selection for specific behaviors may lead to a rebalancing in the immune system.

Comparison of blood parameters in two genetically different groups of horses for functional longevity in show jumping

Introduction

In order to find early selection criteria to improve the longevity of show jumping horses, a specific protocol was designed.

Methods

Before entering competition, young horses selected from extreme stallions for longevity were measured for many traits, including blood parameters. Blood samples were taken from 952 horses aged 2-4 years old, sired by two groups of stallions: one with unfavorable (U) and the other with favorable (F) extreme estimated breeding values for functional longevity. These breeding values were previously calculated from data on 202,320 horses that participated in show jumping competitions between 1985 and 2022. Functional longevity was defined as time spent in competition, adjusted for the level of performance. The 59 measured parameters included hematology, proteins, cytokines, liver and kidney function, bone and joint health, oxidative stress and endocrinology. Heritability was estimated using a mixed model that accounted for the effect of age, sex, estimated weight, visit (place and date of collection), and animal random additive value with 10,280 horses in pedigree. A Partial Least Square logistic regression was performed to predict the sire group.

Results

Age, sex and estimated weight significantly affected 36, 19 and 16 variables, respectively. The visit had a significant effect on all variables. Heritability estimates were high, with 75% higher than 0.20% and 30% higher than 0.50. The most heritable traits included mean corpuscular volume (0.92, se 0.11), mean corpuscular hemoglobin (0.90, se 0.11), white blood cells (0.55, se 0.13), total alkaline phosphatase (0.68, se 0.12) and percentage of γ-globulin (0.57, se 0.12). The logistic regression that predicted the group of sires favorable for longevity identified 16 significant variables. Key findings included: lower mean corpuscular hemoglobin (p-value < 0.001), lower mean corpuscular volume (p-value < 0.001), lower number of white blood cells (p-value < 0.01), higher percentage of intestinal and bone alkaline phosphatase (p-value < 0.01) for a lower total alkaline phosphatase (p-value < 0.01), higher percentage of α2-globulin (p-value < 0.001) and lower percentage of β1-globulin (p-value < 0.01).

Discussion

Blood parameters measured at rest in young horses may be predictive of their genetic value for functional longevity in show jumping.

Immunosenescence and inflammaging in the aged horse

The equine population in the United States and worldwide now includes a higher percentage of geriatric horses than ever previously recorded, and as methods to treat and manage elderly equids are developed and refined, this aging population will likely continue to expand. A better understanding of how horses age and the effect of age on immunity and disease susceptibility is needed to enable targeted preventative healthcare strategies for aged horses. This review article outlines the current state of knowledge regarding the effect of aging on immunity, vaccine responsiveness, and disease risk in the horse, highlighting similarities and differences to what is observed in aged humans. Horses show similar but milder age-related alterations in immune function to those reported in people. Decreases in lymphocyte proliferation and antibody production and diminished response to vaccination have all been documented in elderly horses, however, increased risk of infectious disease is not commonly reported. Aged horses also show evidence of a proinflammatory state (inflammaging) yet appear less susceptible to the chronic diseases of people for which inflammation is a risk factor. Information is currently lacking as to why the horse does not experience the same risk of age-related disease (e.g., cancer, heart disease, neurodegeneration) as people, although a lack of negative lifestyle habits, differences in diet, exercise, genetics and physiology may all contribute to improved health outcomes in the older horse.

Role of the mtDNA Mutations and Mitophagy in Inflammaging

Ageing is an unavoidable multi-factorial process, characterised by a gradual decrease in physiological functionality and increasing vulnerability of the organism to environmental factors and pathogens, ending, eventually, in death. One of the most elaborated ageing theories implies a direct connection between ROS-mediated mtDNA damage and mutations. In this review, we focus on the role of mitochondrial metabolism, mitochondria generated ROS, mitochondrial dynamics and mitophagy in normal ageing and pathological conditions, such as inflammation. Also, a chronic form of inflammation, which could change the long-term status of the immune system in an age-dependent way, is discussed. Finally, the role of inflammaging in the most common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, is also discussed.

Assessment of the impact of age and of blood-derived inflammatory markers in horses with colitis

OBJECTIVES

To determine the impact of age on survival in horses with colitis and to elucidate whether a lower type-1/type-2 cytokine ratio or an exaggerated inflammatory state contribute to reduced survival in aged horses.

DESIGN

Part 1: Retrospective cohort analysis. Part 2: Analytic observational study.

ANIMALS

Part 1: One hundred twenty-four adult horses with colitis. Part 2: Twenty-nine adult horses with new diarrhea onset while hospitalized.

MEASUREMENTS AND MAIN RESULTS

Part 1: Patient signalment, select clinicopathological data, diagnoses, treatment, hospitalization length, and invoice were compared between survivors (n = 101) and nonsurvivors (n = 23). Only age and plasma transfusion retained statistical significance in the final multivariate outcome model, with 8.5 times lower odds of survival in transfused horses (95% confidence interval [CI], 2.6-27.2%). Additionally, the likelihood of nonsurvival increased by 11.8% (95% CI, 4-20.2%) for every year the horse aged (P = 0.002). Similarly, geriatric horses (≥20 years) were 15.2 times more likely to die than young-adults (2-12 years, P = 0.03), independent of financial investment, documented comorbidities, and duration of hospitalization. Part 2: Select cytokine analyses were performed on serum collected from hospitalized horses within 1 hour of diarrhea onset (T0) and 6 hours later. At T0, all recorded clinicopathological variables were comparable between geriatric and young-adult horses, suggesting a similar degree of systemic illness. The median concentration of type-2 cytokines interleukin-4 and interleukin-10, and type-1 cytokine interferon-γ did not differ between age groups. Inflammatory cytokines interleukin-6 and tumor necrosis factor-α were significantly higher in geriatric compared to young-adult horses at both sampling time points.

CONCLUSIONS

Outcome of colitis was less favorable in aging horses and patients receiving a plasma transfusion. Although an exaggerated inflammatory state, based on increased interleukin-6 and tumor necrosis factor-α concentrations, in geriatric horses may contribute to reduced survival, a lower type-1/type-2 cytokines ratio was not identified in our geriatric population.

The Effect of Uterine Lavage on Soluble CD14, Chemokine Ligand 2, and Interleukin 10 Levels in Mares With Postpartum Metritis

Postpartum metritis in mares is a life-threatening condition associated with severe clinical signs due to endotoxemia, and it is often followed by complications such as laminitis. Repeated large-volume uterine lavages are commonly recommended as a part of the treatment protocol to remove endotoxin-laden contents from the uterus. It has, however, also been suggested that lavages may increase the uptake of endotoxin into the circulation, leading to a deterioration of clinical signs. Endotoxemia is associated with the release of a multitude of inflammatory mediators regulating the immune response. The aim of this study was to evaluate if uterine lavage influences serum levels of the inflammation markers soluble CD14 (sCD14), chemokine (C-C motif) ligand 2 (CCL2), and interleukin (IL)-10 in mares with postpartum metritis. Serum samples were collected from eight mares treated for metritis at a university teaching hospital. Mares with fever, tachycardia, and/or leukopenia and hemosanguineous or purulent intrauterine fluid within 1 week of foaling were included in the study. Serum samples were taken before uterine lavage and 15 and 30 minutes after starting the lavage. The concentrations of sCD14, CCL2, and IL-10 were determined with a fluorescent bead-based immunoassay. There were no significant differences between sCD14, CCL2, or IL-10 levels at different sampling times. Heart rate was significantly lower after uterine lavage than before. The differences in body temperature and leukocyte count before and after lavage were not significant. In conclusion, uterine lavage had no immediate effect on the serum concentration of sCD14, CCL2, or IL-10, nor did it affect clinical parameters negatively.

The adjuvant G3 promotes a Th1 polarizing innate immune response in equine PBMC

The immunomodulatory effect of a new particulate adjuvant, G3, alone or in combination with agonists to TLR2/1 or TLR5 was evaluated in cultures of equine PBMC. Exposure to the G3 adjuvant up-regulated genes encoding IFN-γ, IL-1β, IL-6, IL-8, IL-12p40 and IL-23p19 in the majority of the horses tested, indicating that the G3 adjuvant induced a pro-inflammatory and Th1 dominated profile. In accordance, genes encoding IL-13, IL-4, IL-10 and TGF-β remained unaffected and genes encoding IFN-α, IL-17A and TNF-α were only occasionally and weakly induced. The two TLR agonists Pam3CSK4 (TLR2/1) and FliC (TLR5) induced cytokine profiles characterized by a clear induction of IL-10 as well as up-regulation of the genes encoding IL-1β, IL-6 and IL-8. The presence of G3 modified this response, in particular by reducing the FliC and Pam3CSK4 induced production of IL-10. Furthermore, G3 acted in synergy with Pam3CSK4 in enhancing the production of IFN-γ whereas G3 combined with FliC increased the gene expression of IL-8. Thus, the G3 adjuvant seems to have the capacity to promote a Th1 polarizing innate immune response in eqPBMC, both by favouring IFN-γ production and by reducing production of IL-10 induced by co-delivered molecules. These features make G3 an interesting candidate to further evaluate for its potential as an adjuvant in equine vaccines.

Characterization of basal and lipopolysaccharide-induced microRNA expression in equine peripheral blood mononuclear cells using Next-Generation Sequencing

The innate immune response to lipopolysaccharide contributes substantially to the morbidity and mortality of gram-negative sepsis. Horses and humans share an exquisite sensitivity to lipopolysaccharide and thus the horse may provide valuable comparative insights into this aspect of the inflammatory response. MicroRNAs, small non-coding RNA molecules acting as post-transcriptional regulators of gene expression, have key roles in toll-like receptor signaling regulation but have not been studied in this context in horses. The central hypothesis of this study was that lipopolysaccharide induces differential microRNA expression in equine peripheral blood mononuclear cells in a manner comparable to humans. Illumina Next Generation Sequencing was used to characterize the basal microRNA transcriptome in isolated peripheral blood mononuclear cells from healthy adult horses, and to evaluate LPS-induced changes in microRNA expression in cells cultured for up to four hours. Selected expression changes were validated using quantitative reverse-transcriptase PCR. Only miR-155 was significantly upregulated by LPS, changing in parallel with supernatant tumor necrosis factor-α concentration. Eight additional microRNAs, including miR-146a and miR-146b, showed significant expression change with time in culture without a clear LPS effect. Target predictions indicated a number of potential immunity-associated targets for miR-155 in the horse, including SOCS1, TAB2 and elements of the PI3K signaling pathway, suggesting that it is likely to influence the acute inflammatory response to LPS. Gene alignment showed extensive conservation of the miR-155 precursor gene and associated promoter regions between horses and humans. The basal and LPS-stimulated microRNA expression pattern characterized here were similar to those described in human leukocytes. As well as providing a resource for further research into the roles of microRNAs in immune responses in horses, this will facilitate inter-species comparative study of the role of microRNAs in the inflammatory cascade during endotoxemia and sepsis.

Effect of intralesional platelet-rich plasma (PRP) treatment on clinical and ultrasonographic parameters in equine naturally occurring superficial digital flexor tendinopathies - a randomized prospective controlled clinical trial

Background

Regenerative and anti-inflammatory effects on tendinopathies have been attributed to blood-derived biologicals. To date the evidence for the efficacy of autologous platelet-rich plasma (PRP) treatment of naturally occurring equine tendinopathies is limited. The purpose of this placebo-controlled clinical trial was to describe the effect of a single treatment of equine superficial digital flexor tendon (SDFT) disease with PRP on clinical and ultrasonographic parameters. Twenty horses with naturally occurring tendinopathies of forelimb SDFTs were randomly assigned to the PRP-treated group (n = 10) or control group (n = 10) after clinical and ultrasonographic examination. The SDFTs received an intralesional treatment with autologous PRP or were injected with saline, respectively (day 0). All horses participated in a standardized exercise programme and were re-examined clinically, with B-mode ultrasonography (5 times at regular intervals) and ultrasound tissue characterization (week 12 and 24 after treatment) until week 24. Long-term performance was estimated via telephone inquiry.

Results

Compared to day 0, lameness decreased significantly by week 8 after treatment with PRP and by week 12 in the control group. Ultrasonographically there was no difference in the summarized cross sectional area between the groups at any time point. Ultrasound tissue characterization showed that echo types representing disorganized matrix decreased significantly throughout the observation period in the PRP-treated group. Echo type II, representing discontinuous fascicles, not yet aligned into lines of stress was significantly higher 24 weeks after PRP treatment. Eighty percent of the PRP treated horses reached their previous or a higher level of performance after 12 months compared to 50 % in the CG. After 24 months these proportions were 60 % and 50 %, respectively.

Conclusions

A single intralesional treatment with PRP up to 8 weeks after onset of clinical signs of tendinopathy contributes to an earlier reduction of lameness compared to saline treatment and to an advanced organization of repair tissue as the fibrillar matrix is getting organized into fascicles while remodelling continues. Long term, PRP treatment has the potential to increase the number of horses reaching their previous level of performance. Earlier treatment of tendinopathy with PRP should be considered to enhance these effects.

Immune Dysfunction in Aged Horses

The aging process in people is associated with changes in adaptive and innate immune responses. Similar changes occur in aged horses. Age-related progressive impairment in the ability to respond to pathogen challenge and an increased inflammatory reactivity may predispose geriatric horses to many diseases of old age. Specific recommendations for immune modification of older horses, including an age-appropriate vaccination schedule, are not currently available. In addition, the effect of old age on risk of infectious disease is poorly documented. More work is needed to better understand the interactions of age on immunity, vaccine response, and disease risk in horses.

Immune response of healthy horses to DNA constructs formulated with a cationic lipid transfection reagent

Background

Deoxyribonucleic acid (DNA) vaccines are used for experimental immunotherapy of equine melanoma. The injection of complexed linear DNA encoding interleukin (IL)-12/IL-18 induced partial tumour remission in a clinical study including 27 grey horses. To date, the detailed mechanism of the anti-tumour effect of this treatment is unknown.

Results

In the present study, the clinical and cellular responses of 24 healthy horses were monitored over 72 h after simultaneous intradermal and intramuscular application of equine IL-12/IL-18 DNA (complexed with a transfection reagent) or comparative substances (transfection reagent only, nonsense DNA, nonsense DNA depleted of CG).

Although the strongest effect was observed in horses treated with expressing DNA, horses in all groups treated with DNA showed systemic responses. In these horses treated with DNA, rectal temperatures were elevated after treatment and serum amyloid A increased. Total leukocyte and neutrophil counts increased, while lymphocyte numbers decreased. The secretion of tumour necrosis factor alpha (TNFα) and interferon gamma (IFNγ) from peripheral mononuclear blood cells ex vivo increased after treatments with DNA, while IL-10 secretion decreased. Horses treated with DNA had significantly higher myeloid cell numbers and chemokine (C-X-C motif) ligand (CXCL)-10 expression in skin samples at the intradermal injection sites compared to horses treated with transfection reagent only, suggesting an inflammatory response to DNA treatment.

In horses treated with expressing DNA, however, local CXCL-10 expression was highest and immunohistochemistry revealed more intradermal IL-12-positive cells when compared to the other treatment groups.

In contrast to non-grey horses, grey horses showed fewer effects of DNA treatments on blood lymphocyte counts, TNFα secretion and myeloid cell infiltration in the dermis.

Conclusion

Treatment with complexed linear DNA constructs induced an inflammatory response independent of the coding sequence and of CG motif content. Expressing IL-12/IL-18 DNA locally induces expression of the downstream mediator CXCL-10.

The grey horses included appeared to display an attenuated immune response to DNA treatment, although grey horses bearing melanoma responded to this treatment with moderate tumour remission in a preceding study. Whether the different immunological reactivity compared to other horses may contributes to the melanoma susceptibility of grey horses remains to be elucidated.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0452-3) contains supplementary material, which is available to authorized users.