Investigating the contribution of IL-17A and IL-17F to the host response during Escherichia coli mastitis

Bacteriophage-derived endolysins as innovative antimicrobials against bovine mastitis-causing streptococci and staphylococci: a state-of-the-art review

Bacteriophage-encoded endolysins, peptidoglycan hydrolases breaking down the Gram-positive bacterial cell wall, represent a groundbreaking class of novel antimicrobials to revolutionize the veterinary medicine field. Wild-type endolysins exhibit a modular structure, consisting of enzymatically active and cell wall-binding domains, that enable genetic engineering strategies for the creation of chimeric fusion proteins or so-called 'engineered endolysins'. This biotechnological approach has yielded variants with modified lytic spectrums, introducing new possibilities in antimicrobial development. However, the discovery of highly similar endolysins by different groups has occasionally resulted in the assignment of different names that complicate a straightforward comparison. The aim of this review was to perform a homology-based comparison of the wild-type and engineered endolysins that have been characterized in the context of bovine mastitis-causing streptococci and staphylococci, grouping homologous endolysins with ≥ 95.0% protein sequence similarity. Literature is explored by homologous groups for the wild-type endolysins, followed by a chronological examination of engineered endolysins according to their year of publication. This review concludes that the wild-type endolysins encountered persistent challenges in raw milk and in vivo settings, causing a notable shift in the field towards the engineering of endolysins. Lead candidates that display robust lytic activity are nowadays selected from screening assays that are performed under these challenging conditions, often utilizing advanced high-throughput protein engineering methods. Overall, these recent advancements suggest that endolysins will integrate into the antibiotic arsenal over the next decade, thereby innovating antimicrobial treatment against bovine mastitis-causing streptococci and staphylococci.

Homology Modeling, Molecular Dynamics Simulation, and Prediction of Bovine TLR2 Heterodimerization

Toll-like receptor 2 (TLR2) is a major membrane-bound receptor with ligand and species specificity that activates the host immune response. Heterodimerization of TLR2 with TLR1 (TLR2/1) or TLR6 (TLR2/6), triggered by ligand binding, is essential to initiating the signaling pathway. Bovine TLR2 (bTLR2) heterodimerization has not been defined yet compared with human and mouse TLR2s (hTLR2 and mTLR2). The aim of the present study was to model bovine TLRs (TLRs 1, 2 and 6) and create the heterodimeric forms of the bovine TLR2 using molecular dynamics (MD) simulations. We compared the intermolecular interactions in bTLR2/1-PAM3 and bTLR2/6-PAM2 with the hTLR2 and mTLR2 complexes through docking simulations and subsequent MD analyses. The present computational findings showed that bTLR2 dimerization could have a biological function and activate the immune response, similar to hTLR2 and mTLR2. Agonists and antagonists that are designed for hTLR2 and mTLR2 can target bTLR2. However, the experimental approaches to comparing the functional immune response of TLR2 across species were missing in the present study. This computational study provides a structural analysis of the bTLR2 interaction with bTLR1 and bTLR6 in the presence of an agonist/antagonist and reveals the three-dimensional structure of bTLR2 dimerization. The present findings could guide future experimental studies targeting bTLR2 with different ligands and lipopeptides.

Mammary γδ T cells promote IL-17A-mediated immunity against Staphylococcus aureus-induced mastitis in a microbiota-dependent manner

Mastitis, a common disease for female during lactation period that could cause a health risk for human or huge economic losses for animals, is mainly caused by S. aureus invasion. Here, we found that neutrophil recruitment via IL-17A-mediated signaling was required for host defense against S. aureus-induced mastitis in a mouse model. The rapid accumulation and activation of Vγ4+ γδ T cells in the early stage of infection triggered the IL-17A-mediated immune response. Interestingly, the accumulation and influence of γδT17 cells in host defense against S. aureus-induced mastitis in a commensal microbiota-dependent manner. Overall, this study, focusing on γδT17 cells, clarified innate immune response mechanisms against S. aureus-induced mastitis, and provided a specific response to target for future immunotherapies. Meanwhile, a link between commensal microbiota community and host defense to S. aureus mammary gland infection may unveil potential therapeutic strategies to combat these intractable infections.

Transcriptomic profiling of lipopolysaccharide-challenged bovine mammary epithelial cells treated with forsythoside A

Mastitis is usually caused by a variety of pathogenic bacteria that seriously impact the health and milk-production ability of dairy cows, with consequent, economically detrimental effects on the dairy industry. Forsythoside A (FTA), isolated from the fruit and leaves of Forsythia suspensa (Thunb.) Vahl (Oleaceae), has been reported to have significant antioxidant, anti-inflammatory, and antibacterial effects. However, it is not clear whether FTA exerts a protective effect against lipopolysaccharide (LPS)-induced bovine mastitis and its potential gene signature. In this study, high-throughput sequencing technology was performed to analyze the differences between the mRNA and enrichment pathway of bovine mammary epithelial cells of the control, LPS, and LPS + FTA groups. The results showed that there were 139 differentially expressed genes (DEGs) (p-value < 0.05, |log2FoldChange| > 1, FPKM > 1) in the LPS group compared with the control group, including 121 up-regulated genes and 18 down-regulated genes, which were mainly enriched in the cellular response to lipopolysaccharide, cytokine activity, protein binding, and IL-17 signaling pathway based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, respectively. Compared with the control group and LPS + FTA group, there were 349 DEGs, including 322 up-regulated genes and 27 down-regulated genes. They were mainly enriched in protein localization to organelles, centrosomes, binding, and the IL-17 signaling pathway, based on GO and KEGG analysis. Compared to the LPS group, the LPS + FTA group had 272 DEGs, including 259 up-regulated genes and 13 down-regulated genes, which were mainly enriched in RNA processing, IL-6 receptor binding, and the lysosome pathway, based on GO and KEGG analyses. It can be seen that LPS stimulation induced the expression of inflammation-related genes, IL-17 and IL-6, whereas FTA treatment promoted the expression of the spliceosome-, lysosome-, and oxidative stress-related genes HSP70, HSPA8, and PARP2. The study utilized RNA-sequencing analysis of FTA against LPS-challenged bovine mammary epithelial cells to explore key mRNA findings that may be strongly associated with inflammation and oxidative stress, and provides a theoretical reference for further elucidation of molecular mechanisms of bovine mastitis and therapeutic effects of FTA against bovine mastitis.

Immune defences of the mammary gland in dairy ruminants

The mammary gland (MG) of ruminants is essential for assuring the immune protection and nutrition of the suckling youngs. The domestication of these species aimed at increasing milk production for human consumption enhanced udder susceptibility to infections and in this context, a better understanding of the MG immune defences has become a cornerstone for the success of dairy farming. In this review, we explore constitutive and inducible immune mechanisms of the mammary gland and briefly discuss the knowledge gaps that remain to be elucidated for the implementation of strategies focused on boosting mammary immune responses.

Advances in Diagnostic Approaches and Therapeutic Management in Bovine Mastitis

Mastitis causes huge economic losses to dairy farmers worldwide, which largely negatively affects the quality and quantity of milk. Mastitis decreases overall milk production, degrades milk quality, increases milk losses because of milk being discarded, and increases overall production costs due to higher treatment and labour costs and premature culling. This review article discusses mastitis with respect to its clinical epidemiology, the pathogens involved, economic losses, and basic and advanced diagnostic tools that have been used in recent times to diagnose mastitis effectively. There is an increasing focus on the application of novel therapeutic approaches as an alternative to conventional antibiotic therapy because of the decreasing effectiveness of antibiotics, emergence of antibiotic-resistant bacteria, issue of antibiotic residues in the food chain, food safety issues, and environmental impacts. This article also discussed nanoparticles'/chitosan's roles in antibiotic-resistant strains and ethno-veterinary practices for mastitis treatment in dairy cattle.

Punch-excised explants of bovine mammary gland to model early immune response to infection

BACKGROUND

Mammary gland (MG) infections (mastitis) are frequent diseases of dairy cows that affect milk quality, animal welfare and farming profitability. These infections are commonly associated with the bacteria Escherichia coli and Staphylococcus aureus. Different in vitro models have been used to investigate the early response of the MG to bacteria, but the role of the teat in mastitis pathogenesis has received less attention. In this study, we used punch-excised teat tissue as an ex vivo model to study the immune mechanisms that arise early during infection when bacteria have entered the MG.

RESULTS

Cytotoxicity and microscopic analyses showed that bovine teat sinus explants have their morphology and viability preserved after 24 h of culture and respond to ex vivo stimulation with TLR-agonists and bacteria. LPS and E. coli trigger stronger inflammatory response in teat when compared to LTA and S. aureus, leading to a higher production of IL-6 and IL-8, as well as to an up-regulation of proinflammatory genes. We also demonstrated that our ex vivo model can be applied to frozen-stored explants.

CONCLUSIONS

In compliance with the 3Rs principle (replacement, reduction and refinement) in animal experimentation, ex vivo explant analyses proved to be a simple and affordable approach to study MG immune response to infection. This model, which better reproduces organ complexity than epithelial cell cultures or tissue slices, lends itself particularly well to studying the early phases of the MG immune response to infection.

Transcriptome-wide mapping of milk somatic cells upon subclinical mastitis infection in dairy cattle

BACKGROUND

Subclinical intramammary infection (IMI) represents a significant problem in maintaining dairy cows' health. Disease severity and extent depend on the interaction between the causative agent, environment, and host. To investigate the molecular mechanisms behind the host immune response, we used RNA-Seq for the milk somatic cells (SC) transcriptome profiling in healthy cows (n = 9), and cows naturally affected by subclinical IMI from Prototheca spp. (n = 11) and Streptococcus agalactiae (S. agalactiae; n = 11). Data Integration Analysis for Biomarker discovery using Latent Components (DIABLO) was used to integrate transcriptomic data and host phenotypic traits related to milk composition, SC composition, and udder health to identify hub variables for subclinical IMI detection.

RESULTS

A total of 1,682 and 2,427 differentially expressed genes (DEGs) were identified when comparing Prototheca spp. and S. agalactiae to healthy animals, respectively. Pathogen-specific pathway analyses evidenced that Prototheca's infection upregulated antigen processing and lymphocyte proliferation pathways while S. agalactiae induced a reduction of energy-related pathways like the tricarboxylic acid cycle, and carbohydrate and lipid metabolism. The integrative analysis of commonly shared DEGs between the two pathogens (n = 681) referred to the core-mastitis response genes, and phenotypic data evidenced a strong covariation between those genes and the flow cytometry immune cells (r² = 0.72), followed by the udder health (r² = 0.64) and milk quality parameters (r² = 0.64). Variables with r ≥ 0.90 were used to build a network in which the top 20 hub variables were identified with the Cytoscape cytohubba plug-in. The genes in common between DIABLO and cytohubba (n = 10) were submitted to a ROC analysis which showed they had excellent predictive performances in terms of discriminating healthy and mastitis-affected animals (sensitivity > 0.89, specificity > 0.81, accuracy > 0.87, and precision > 0.69). Among these genes, CIITA could play a key role in regulating the animals' response to subclinical IMI.

CONCLUSIONS

Despite some differences in the enriched pathways, the two mastitis-causing pathogens seemed to induce a shared host immune-transcriptomic response. The hub variables identified with the integrative approach might be included in screening and diagnostic tools for subclinical IMI detection.

Genetic polymorphisms in immune- and inflammation-associated genes and their association with bovine mastitis resistance/susceptibility

Bovine mastitis, the inflammation of the mammary gland, is a contagious disease characterized by chemical and physical changes in milk and pathological changes in udder tissues. Depressed immunity and higher expression of inflammatory cytokines with an elevated milk somatic cell count can be observed during mastitis in dairy cattle. The use of somatic cell count (SCC) and somatic cell score (SCS) as correlated traits in the indirect selection of animals against mastitis resistance is in progress globally. Traditional breeding for mastitis resistance seems difficult because of the low heritability (0.10-0.16) of SCC/SCS and clinical mastitis. Thus, genetic-marker-selective breeding to improve host genetics has attracted considerable attention worldwide. Moreover, genomic selection has been found to be an effective and fast method of screening for dairy cattle that are genetically resistant and susceptible to mastitis at a very early age. The current review discusses and summarizes the candidate gene approach using polymorphisms in immune- and inflammation-linked genes (CD4, CD14, CD46, TRAPPC9, JAK2, Tf, Lf, TLRs, CXCL8, CXCR1, CXCR2, C4A, C5, MASP2, MBL1, MBL2, LBP, NCF1, NCF4, MASP2, A2M, and CLU, etc.) and their related signaling pathways (Staphylococcus aureus infection signaling, Toll-like receptor signaling, NF-kappa B signaling pathway, Cytokine-cytokine receptor, and Complement and coagulation cascades, etc.) associated with mastitis resistance and susceptibility phenotypic traits (IL-6, interferon-gamma (IFN-γ), IL17, IL8, SCS, and SCC) in dairy cattle.

RNA-seq reveals the role of miR-199a-3p in regulating inflammation of bovine mammary epithelial cells

MicroRNAs (miRNAs) are involved in the regulation of a variety of biological processes. However, the research on the regulatory role of bovine mammary epithelial cells (bMECs) is scarce. To date, there are no reports about the role of miR-199a-3p in bMECs. In this study, RNA sequencing (RNA-seq) technology was used to detect the transcriptomes of the miR-199a-3p overexpression and negative control (NC) groups of bMECs. Then, the screening and functional annotation of differentially expressed genes (DEGs) were conducted. The results showed that there were 140 DEGs (109 up-regulated and 31 down-regulated) in the miR-199a-3p overexpression group. The results of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses indicated that the DEGs might regulate the immune and inflammatory responses via the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway, transforming growth factor-beta (TGF-β) signaling pathway, and interleukin-17 (IL-17) signaling pathway, which revealed that miR-199a-3p might participate in regulating bMECs inflammation via affecting the expression of related genes and the above signaling pathways. This study may provide a new reference for potential therapeutic targets of cow mastitis.

Phenotype of Coxiella burnetii Strains of Different Sources and Genotypes in Bovine Mammary Gland Epithelial Cells

Despite the high prevalence of C. burnetii in dairy herds and continuous shedding via milk by chronically infected cows, bovine milk is not recognized as a relevant source of human Q fever. We hypothesized that the bovine mammary gland epithelial cell line PS represents a suitable in vitro model for the identification of C. burnetii-strain-specific virulence properties that may account for this discrepancy. Fifteen C. burnetii strains were selected to represent different host species and multiple loci variable number of tandem repeat analysis (MLVA) genotypes (I, II, III and IV). The replication efficiencies of all strains were similar, even though strains of the MLVA-genotype II replicated significantly better than genotype I strains, and bovine and ovine isolates replicated better than caprine ones. Bovine milk isolates replicated with similar efficiencies to isolates from other bovine organs. One sheep isolate (Cb30/14, MLVA type I, isolated from fetal membranes) induced a remarkable up-regulation of IL-1β and TNF-α, whereas prototypic strains and bovine milk isolates tended to suppress pro-inflammatory responses. While infection with strain Nine Mile I rendered the cells partially refractory to re-stimulation with E. coli lipopolysaccharide, Cb30/14 exerted a selective suppressive effect which was restricted to IL-6 and TNF-α and spared IL-1β. PS cells support the replication of different strains of C. burnetii and respond in a strain-specific manner, but isolates from bovine milk did not display a common pattern, which distinguishes them from strains identified as a public health concern.

Immune defenses of the mammary gland epithelium of dairy ruminants

The epithelium of the mammary gland (MG) fulfills three major functions: nutrition of progeny, transfer of immunity from mother to newborn, and its own defense against infection. The defense function of the epithelium requires the cooperation of mammary epithelial cells (MECs) with intraepithelial leucocytes, macrophages, DCs, and resident lymphocytes. The MG is characterized by the secretion of a large amount of a nutrient liquid in which certain bacteria can proliferate and reach a considerable bacterial load, which has conditioned how the udder reacts against bacterial invasions. This review presents how the mammary epithelium perceives bacteria, and how it responds to the main bacterial genera associated with mastitis. MECs are able to detect the presence of actively multiplying bacteria in the lumen of the gland: they express pattern recognition receptors (PRRs) that recognize microbe-associated molecular patterns (MAMPs) released by the growing bacteria. Interactions with intraepithelial leucocytes fine-tune MECs responses. Following the onset of inflammation, new interactions are established with lymphocytes and neutrophils recruited from the blood. The mammary epithelium also identifies and responds to antigens, which supposes an antigen-presenting capacity. Its responses can be manipulated with drugs, plant extracts, probiotics, and immune modifiers, in order to increase its defense capacities or reduce the damage related to inflammation. Numerous studies have established that the mammary epithelium is a genuine effector of both innate and adaptive immunity. However, knowledge gaps remain and newly available tools offer the prospect of exciting research to unravel and exploit the multiple capacities of this particular epithelium.

Polymorphisms of the IL-17A Gene Influence Milk Production Traits and Somatic Cell Score in Chinese Holstein Cows

The cow’s milk production characteristics are a significant economic indicator in the livestock industry. Serum cytokines such as interleukin-17 (IL-17) may be potential indicators for bovine mastitis concerning the milk somatic cell count (SCC) and somatic cell score (SCS). The current study aims to find previously undiscovered single nucleotide polymorphisms in the bovine (IL-17A) gene and further investigates their associations with milk production traits in Chinese Holstein cows. Twenty Chinese Holstein cows were randomly chosen from six farms in Jiangsu Province, China. The DNA was extracted from selected samples of bloods for PCR amplification Sequence analyses were used to find SNPs in the bovine (IL-17A) gene. The discovered five SNPs are g-1578A>G, g-1835G>A, and g-398T>A in the 5′UTR; g3164T>C and g3409G>C in the exon region. The genotyping of Holstein cows (n = 992) was performed based on Sequenom Mass ARRAY and SNP data. The connection between SNPs, milk production variables, and the somatic cell score was investigated using the least-squares method. Based on the results, SNP g-398T>A had a significant linkage disequilibrium with g3164T>C. SNPs were found to have significant (p < 0.05) correlations with the test-day milk yield. In conclusion, IL-17A affects cow’s milk production traits significantly.

Escherichia coli Mastitis in Dairy Cattle: Etiology, Diagnosis, and Treatment Challenges

Bovine mastitis is an inflammation of the udder tissue parenchyma that causes pathological changes in the glandular tissue and abnormalities in milk leading to significant economic losses to the dairy industry across the world. Mammary pathogenic Escherichia (E.) coli (MPEC) is one of the main etiologic agents of acute clinical mastitis in dairy cattle. MPEC strains have virulence attributes to resist the host innate defenses and thrive in the mammary gland environment. The association between specific virulence factors of MPEC with the severity of mastitis in cattle is not fully understood. Furthermore, the indiscriminate use of antibiotics to treat mastitis has resulted in antimicrobial resistance to all major antibiotic classes in MPEC. A thorough understanding of MPEC’s pathogenesis and antimicrobial susceptibility pattern is required to develop better interventions to reduce mastitis incidence and prevalence in cattle and the environment. This review compiles important information on mastitis caused by MPEC (e.g., types of mastitis, host immune response, diagnosis, treatment, and control of the disease) as well as the current knowledge on MPEC virulence factors, antimicrobial resistance, and the dilemma of MPEC as a new pathotype. The information provided in this review is critical to identifying gaps in knowledge that will guide future studies to better design diagnostic, prevent, and develop therapeutic interventions for this significant dairy disease.

Identification of Inflammatory and Regulatory Cytokines IL-1α-, IL-4-, IL-6-, IL-12-, IL-13-, IL-17A-, TNF-α-, and IFN-γ-Producing Cells in the Milk of Dairy Cows with Subclinical and Clinical Mastitis

In naturally occurring bovine mastitis, effects of infection depend on the host inflammatory response, including the effects of secreted cytokines. Knowledge about the inflammatory and regulatory cytokines in milk cells of free-stall barn dairy cows and in naturally occurring mastitis is lacking as most studies focus on induced mastitis. Hereby, the aim of the study was to determine inflammatory and regulatory cytokines in the milk of dairy cows with subclinical and clinical mastitis. The following examinations of milk samples were performed: differential counting of somatic cells (SCC), bacteriological examination, and immunocytochemical analysis. Mean SCC increased in subclinical and clinical mastitis cases. The number of pathogenic mastitis-causing bacteria on plates increased in subclinical mastitis cases but decreased in clinical mastitis. The inflammatory and regulatory markers in the milk cells of healthy cows showed the highest mean cell numbers (%). In mastitis cases, immunoreactivity was more pronounced for IL-4, IL-6, IL-12, IL-13, IL-17A, TNF-α, and IFN-γ. Data about subclinical and clinical mastitis demonstrate inflammatory responses to intramammary infection driven by IL-1α, IL-4, and IL-17A. Moreover, the host defense response in mastitis is characterized by continuation or resolution of initial inflammation. IL-12 and INF-γ immunoreactivity was recognized to differ mastitis cases from the relative health status.

Progress towards the Elusive Mastitis Vaccines

Mastitis is a major problem in dairy farming. Vaccine prevention of mammary bacterial infections is of particular interest in helping to deal with this issue, all the more so as antibacterial drug inputs in dairy farms must be reduced. Unfortunately, the effectiveness of current vaccines is not satisfactory. In this review, we examine the possible reasons for the current shortcomings of mastitis vaccines. Some reasons stem from the peculiarities of the mammary gland immunobiology, others from the pathogens adapted to the mammary gland niche. Infection does not induce sterilizing protection, and recurrence is common. Efficacious vaccines will have to elicit immune mechanisms different from and more effective than those induced by infection. We propose focusing our research on a few points pertaining to either the current immune knowledge or vaccinology approaches to get out of the current deadlock. A possible solution is to focus on the contribution of cell-mediated immunity to udder protection based on the interactions of T cells with the mammary epithelium. On the vaccinology side, studies on the orientation of the immune response by adjuvants, the route of vaccine administration and the delivery systems are among the keys to success.

An overview on mastitis-associated Escherichia coli: Pathogenicity, host immunity and the use of alternative therapies

Escherichia coli is one of the leading causes of bovine mastitis; it can cause sub-clinical, and clinical mastitis characterized by systemic changes, abnormal appearance of milk, and udder inflammation. E. coli pathogenicity in the bovine udder is due to the interaction between its virulence factors and the host factors; it was also linked to the presence of a new pathotype termed mammary pathogenic E. coli (MPEC). However, the presence of this pathotype is commonly debated. Its main virulence factor is the lipopolysaccharide (LPS) that is responsible for causing an endotoxic shock, and inducing a strong immune response by binding to the toll-like receptor 4 (TLR4), and stimulating the expression of chemokines (such as IL-8, and RANTES) and pro-inflammatory cytokines (such as IL-6, and IL-1β). This strong immune response could be used to develop alternative and safe approaches to control E. coli causing bovine mastitis by targeting pro-inflammatory cytokines that can damage the host tissue. The need for alternative treatments against E. coli is due to its ability to resist many conventional antibiotics, which is a huge challenge for curing ill animals. Therefore, the aim of this review was to highlight the pathogenicity of E. coli in the mammary gland, discuss the presence of the new putative pathotype, the mammary pathogenic E. coli (MPEC) pathotype, study the host's immune response, and the alternative treatments that are used against mastitis-associated E. coli.

Intramammary Immunisation Provides Short Term Protection Against Mannheimia haemolytica Mastitis in Sheep

Mastitis affects both dairy and meat/wool sheep industries with losses due to reductions in milk quality and quantity, increased treatment costs and restricted lamb growth. Effective vaccines would be important tools for mastitis control. However, the development of vaccines against mastitis has proved challenging due to the failure to target protective immunity to the mammary gland. In order to target responses to the mammary gland, this study tested whether local administration directly into the gland through the teat canal or in the udder skin confers protection against an intramammary infection. In this study, we tested a vaccine that confers protection against respiratory disease caused by Mannheimia haemolytica to determine if it also protects against intramammary infection by the same organism. No evidence of protection was observed in animals that received a subcutaneous immunisation in the udder skin, however, intramammary immunisation provided almost complete protection against an experimental challenge administered 7 days post immunisation but not if the challenge was delivered 14 days post immunisation. To investigate further the nature of this variation in response, the somatic cell count and concentration of cytokines Interleukin-1β, Interleukin-10 and Interleukin-17A was determined in milk over the course of each study. Intramammary immunisation induced an inflammatory response within the mammary gland, characterised by increases in SCC and in the production of cytokines IL-1β, IL-10, and IL-17A. This response was similar to that observed in un-vaccinated control animals post challenge. The SCC and cytokine levels had returned to levels comparable with un-vaccinated controls prior to challenge at both 7 and 14 days post immunisation. The transient nature of the protective effect is consistent with the priming of an innate antibacterial response within the mammary gland which provides protection against challenge at 7 days but is diminished by 14 days post-vaccination. Further studies are planned to determine the nature of the innate immune mechanisms associated with the protective effect described here to determine whether it may be exploited to improve ruminant udder health.

Bovine Teat Cistern Microbiota Composition and Richness Are Associated With the Immune and Microbial Responses During Transition to Once-Daily Milking

The relationship between microbiota and health has been widely reported in humans and animals. We established a link between teat cistern microbiota composition and bovine mastitis, an inflammatory disease often due to bacterial infections. To further decipher the relationships between teat cistern microbiota and immune and microbial responses, a switch from twice- to once-daily milking (ODM) in 31 initially healthy quarters of dairy cows was used to trigger an udder perturbation. In this study, a temporal relationship was reported between initial teat cistern microbiota composition and richness, the immune response to ODM, and mastitis development. Quarters with a low initial microbiota richness and taxonomic markers such as Bacteroidetes and Proteobacteria were associated with a higher rate of mastitis during ODM. Quarters with a higher richness and taxonomic markers such as Firmicutes, including the Lachnospiraceae family, and genera such as Bifidobacterium and Corynebacterium displayed early inflammation following transition to ODM but without developing mastitis (no infection). Short-term compositional shifts of microbiota indicates that microbiotas with a higher initial richness were more strongly altered by transition to ODM, with notably the disappearance of rare OTUs. Microbiota modifications were associated with an early innate immune system stimulation, which, in turn, may have contributed to the prevention of mastitis development.

Heat inactivation partially preserved barrier and immunomodulatory effects of Lactobacillus gasseri LA806 in an in vitro model of bovine mastitis

Probiotics could help combat infections and reduce antibiotic use. As use of live bacteria is limited in some cases by safety or regulatory concerns, the potential of inactivated bacteria is worth investigating. We evaluated the potential of live and heat-inactivated Lactobacillus gasseri LA806 to counteract Staphylococcus aureus and Escherichia coli infection cycles in an in vitro model of bovine mastitis. We assessed the ability of live and inactivated LA806 to impair pathogen colonisation of bovine mammary epithelial cells (bMECs) and to modulate cytokine expression by pathogen-stimulated bMECs. Live LA806 induced a five-fold decrease in S. aureus adhesion and internalisation (while not affecting E. coli colonisation) and decreased pro-inflammatory cytokine expression by S. aureus-stimulated bMECs (without interfering with the immune response to E. coli). The ability of inactivated LA806 ability to diminish S. aureus colonisation was two-fold lower than that of the live strain, but its anti-inflammatory properties were barely impacted. Even though LA806 effects were impaired after inactivation, both live and inactivated LA806 have barrier and immunomodulatory properties that could be useful to counteract S. aureus colonisation in the bovine mammary gland. As S. aureus is involved in various types of infection, LA806 potential would worth exploring in other contexts.

Th17-related mammary immunity, but not a high systemic Th1 immune response is associated with protection against E. coli mastitis

Vaccination against bovine mastitis lags behind despite high demand from the dairy industry and margin for efficacy improvement. We previously compared two immunization protocols against E. coli using either only the intramuscular route or a combination of intramuscular and mammary ductal routes, also known as 'prime and pull' strategy. A homologous mammary challenge during the memory phase showed that immunization favorably modified the mastitis course, notably in locally immunized cows in comparison to intramuscular and control adjuvant-only groups. Here, we performed whole-blood profiling through RNA-seq transcriptome and plasma cytokine 15-plex analyses at time points of the E. coli mastitis that showed significant clinical and laboratory differences among the groups. Diminished production of inflammatory cytokines and increased IFNγ were detected in the blood of immunized cows, where a T lymphocyte activation profile was evidenced at 12-h post infection. Acute phase neutropenia was less severe in these cows, and pathways related to neutrophil diapedesis and monocyte activation were also present. Furthermore, three intramammary-immunized cows showing faster healing and shorter mastitis duration had gene profiles that differed from their counterparts, but without any clue for the mastitis susceptibility difference. Inasmuch, when gene expression of CD4 T cells was assessed in mammary tissue, enrichment of IL-17-associated pathways was identified in the quarters of intramammary-immunized cows not only after challenge but also in the control quarters that were not infected. These findings indicate that local immunization mobilizes protective mechanisms that rely on the settlement of type 3 immunity-related CD4 T cells prior to infection.

Role of the JAK-STAT Pathway in Bovine Mastitis and Milk Production

Simple Summary

The cytokine-activated Janus kinase (JAK)—signal transducer and activator of transcription (STAT) pathway has an important role in the regulation of immunity and inflammation. In addition, the signaling of this pathway has been reported to be associated with mammary gland development and milk production. Because of such important functions, the JAK-STAT pathway has been widely targeted in both human and animal diseases as a therapeutic agent. Recently, the JAK2, STATs, and inhibitors of the JAK-STAT pathway, especially cytokine signaling suppressors (SOCSs), have been reported to be associated with milk production and mastitis-resistance phenotypic traits in dairy cattle. Thus, in the current review, we attempt to overview the development of the JAK-STAT pathway role in bovine mastitis and milk production.

Abstract

The cytokine-activated Janus kinase (JAK)—signal transducer and activator of transcription (STAT) pathway is a sequence of communications between proteins in a cell, and it is associated with various processes such as cell division, apoptosis, mammary gland development, lactation, anti-inflammation, and immunity. The pathway is involved in transferring information from receptors on the cell surface to the cell nucleus, resulting in the regulation of genes through transcription. The Janus kinase 2 (JAK2), signal transducer and activator of transcription A and B (STAT5 A & B), STAT1, and cytokine signaling suppressor 3 (SOCS3) are the key members of the JAK-STAT pathway. Interestingly, prolactin (Prl) also uses the JAK-STAT pathway to regulate milk production traits in dairy cattle. The activation of JAK2 and STATs genes has a critical role in milk production and mastitis resistance. The upregulation of SOCS3 in bovine mammary epithelial cells inhibits the activation of JAK2 and STATs genes, which promotes mastitis development and reduces the lactational performance of dairy cattle. In the current review, we highlight the recent development in the knowledge of JAK-STAT, which will enhance our ability to devise therapeutic strategies for bovine mastitis control. Furthermore, the review also explores the role of the JAK-STAT pathway in the regulation of milk production in dairy cattle.

Enterobactin Deficiency in a Coliform Mastitis Isolate Decreases Its Fitness in a Murine Model: A Preliminary Host-Pathogen Interaction Study

Iron is an essential nutrient for bacterial growth. Therefore, bacteria have evolved chelation mechanisms to acquire iron for their survival. Enterobactin, a chelator with high affinity for ferric iron, is secreted by Escherichia coli and contributes to its improved bacterial fitness. In this preliminary study, we evaluated enterobactin deficiency both in vitro and in vivo in the context of E. coli mastitis. Firstly, we showed that expression of lipocalin 2, a protein produced by the host that is able to both bind and deplete enterobactin, is increased upon E. coli infection in the cow's mastitic mammary gland. Secondly, we demonstrated in vitro that enterobactin deficiency does not alter interleukin (IL)-8 expression in bovine mammary epithelial cells and its associated neutrophil recruitment. However, a significantly increased reactive oxygen species production of these neutrophils was observed. Thirdly, we showed there was no significant difference in bacterial in vitro growth between the enterobactin-deficient mutant and its wild-type counterpart. However, when further explored in a murine model for bovine mastitis, the enterobactin-deficient mutant vs. the wild-type strain revealed a significant reduction of the bacterial load and, consequently, a decrease in pro-inflammatory cytokines (IL-1α,-1β,-4,-6, and-8). A reduced neutrophilic influx was also observed immunohistochemically. These findings therefore identify interference of the enterobactin iron-scavenging mechanism as a potential measure to decrease the fitness of E. coli in the mastitic mammary gland.

Type 3 immunity: a perspective for the defense of the mammary gland against infections

Type 3 immunity encompasses innate and adaptive immune responses mediated by cells that produce the signature cytokines IL-17A and IL-17F. This class of effector immunity is particularly adept at controlling infections by pyogenic extracellular bacteria at epithelial barriers. Since mastitis results from infections by bacteria such as streptococci, staphylococci and coliform bacteria that cause neutrophilic inflammation, type 3 immunity can be expected to be mobilized at the mammary gland. In effect, the main defenses of this organ are provided by epithelial cells and neutrophils, which are the main terminal effectors of type 3 immunity. In addition to theoretical grounds, there is observational and experimental evidence that supports a role for type 3 immunity in the mammary gland, such as the production of IL-17A, IL-17F, and IL-22 in milk and mammary tissue during infection, although their respective sources remain to be fully identified. Moreover, mouse mastitis models have shown a positive effect of IL-17A on the course of mastitis. A lot remains to be uncovered before we can safely harness type 3 immunity to reinforce mammary gland defenses through innate immune training or vaccination. However, this is a promising way to find new means of improving mammary gland defenses against infection.

Multilocus sequence typing characterizes diversity of Ureaplasma diversum strains, and intra-species variability induces different immune response profiles

Background

Ureaplasma diversum is a pathogen found in the genital tract of cattle and associated with genital disorders such as infertility, placentitis, abortion, birth of weak calves, low sperm motility, seminal vesiculitis and epididymitis. There are few studies evaluating the genetic diversity of U. diversum strains and their influence on the immune response in cattle. Therefore, to better understand genetic relationships of the pathogenicity of U. diversum, a multilocus sequence typing (MLST) scheme was performed to characterize the ATCC 49782 strain and another 40 isolates recovered from different Brazilian states.

Results

Primers were designed for housekeeping genes ftsH, polC, rpL22, rpoB, valS and ureA and for virulence genes, phospholipase D (pld), triacylglycerol lipase (tgl), hemolysin (hlyA), MIB-MIP system (mib,mip), MBA (mba), VsA (VsA) and ribose transporter (tABC). PCRs were performed and the targeted gene products were purified and sequenced. Sequence types (STs), and clonal complexes (CCs) were assigned and the phylogenetic relationship was also evaluated. Thus, a total of 19 STs and 4 CCs were studied. Following the molecular analysis, six isolates of U. diversum were selected, inoculated into bovine monocyte/macrophage culture and evaluated for gene expression of the cytokines TNF-α, IL-1, IL-6, IL-10 and IL-17. Differences were detected in the induction of cytokines, especially between isolates 198 and BA78, promoted inflammatory and anti-inflammatory profiles, respectively, and they also differed in virulence factors.

Conclusion

It was observed that intra-species variability between isolates of U. diversum can induce variations of virulent determinants and, consequently, modulate the expression of the triggered immune response.

Milk Microbiota: What Are We Exactly Talking About?

The development of powerful sequencing techniques has allowed, albeit with some biases, the identification and inventory of complex microbial communities that inhabit different body sites or body fluids, some of which were previously considered sterile. Notably, milk is now considered to host a complex microbial community with great diversity. Milk microbiota is now well documented in various hosts. Based on the growing literature on this microbial community, we address here the question of what milk microbiota is. We summarize and compare the microbial composition of milk in humans and in ruminants and address the existence of a putative core milk microbiota. We discuss the factors that contribute to shape the milk microbiota or affect its composition, including host and environmental factors as well as methodological factors, such as the sampling and sequencing techniques, which likely introduce distortion in milk microbiota analysis. The roles that milk microbiota are likely to play in the mother and offspring physiology and health are presented together with recent data on the hypothesis of an enteromammary pathway. At last, this fascinating field raises a series of questions, which are listed and commented here and which open new research avenues.

Adaptive immunity in the postpartum uterus: Potential use of vaccines to control metritis

After parturition, dairy cows rely on an effective innate immune response, through the actions of neutrophils, macrophages, and antimicrobial peptides, to clear the uterus from pathogenic bacteria, such as E. coli, Bacteroides spp, F. necrophorum and T. pyogenes. However, the role of adaptive immunity in the postpartum uterus is less understood. In this review, we explore concepts of mucosal adaptive immunity and discuss recent findings regarding the efficacy of vaccines to reduce metritis in dairy cows. Areas of lymphocytic aggregates are seen throughout the bovine reproductive tract after parturition, but it is unknown if their development is influenced by previous exposure to pathogens or other intrinsic factors. Through the actions of Treg cells and γδ T cells, the uterus is an immune-tolerant environment during pregnancy. After parturition, the dynamics in the endometrial and circulating lymphocytic populations differ among cows that develop uterine diseases and healthy counterparts. However, the functionality of those cells has not yet been determined. It has been hypothesized that cows that fail to switch their uterine environment from an anti-inflammatory state prior to parturition to a pro-inflammatory state after calving are more susceptible to uterine infections. Given the nature of metritis related pathogens and the importance of innate immunity to uterine defense mechanisms, we speculate that an adaptive immunity biased towards a Th1/Th17 cellular response will provide best protection against uterine infections. Few studies have evaluated the efficacy of immunization in reducing the incidence of metritis in dairy cows revealing inconsistent findings.

Activation of a Bovine Mammary Epithelial Cell Line by Ruminant-Associated Staphylococcus aureus is Lineage Dependent

Bovine mastitis is a costly disease to the dairy industry and intramammary infections (IMI) with Staphylococcus aureus are a major cause of mastitis. Staphylococcus aureus strains responsible for mastitis in cattle predominantly belong to ruminant-associated clonal complexes (CCs). Recognition of pathogens by bovine mammary epithelial cells (bMEC) plays a key role in activation of immune responsiveness during IMI. However, it is still largely unknown to what extent the bMEC response differs according to S. aureus CC. The aim of this study was to determine whether ruminant-associated S. aureus CCs differentially activate bMEC. For this purpose, the immortalized bMEC line PS was stimulated with S. aureus mastitis isolates belonging to four different clonal complexes (CCs; CC133, CC479, CC151 and CC425) and interleukin 8 (IL-8) release was measured as indicator of activation. To validate our bMEC model, we first stimulated PS cells with genetically modified S. aureus strains lacking (protein A, wall teichoic acid (WTA) synthesis) or expressing (capsular polysaccharide (CP) type 5 or type 8) factors expected to affect S. aureus recognition by bMEC. The absence of functional WTA synthesis increased IL-8 release by bMEC in response to bacterial stimulation compared to wildtype. In addition, bMEC released more IL-8 after stimulation with S. aureus expressing CP type 5 compared to CP type 8 or a strain lacking CP expression. Among the S. aureus lineages, isolates belonging to CC133 induced a significantly stronger IL-8 release from bMEC than isolates from the other CCs, and the IL-8 response to CC479 was higher compared to CC151 and CC425. Transcription levels of IL-8, tumor necrosis factor alpha (TNFα), serum amyloid A3 (SAA3), Toll-like receptor (TLR)-2 and nuclear factor κB (NF-κB) in bMEC after bacterial stimulation tended to follow a similar pattern as IL-8 release, but there were no significant differences between the CCs. This study demonstrates a differential activation of bMEC by ruminant-associated CCs of S. aureus, which may have implications for the severity of mastitis during IMI by S. aureus belonging to these lineages.

Expansion, isolation and first characterization of bovine Th17 lymphocytes

Interleukin 17A-producing T helper cells (Th17) are CD4+ T cells that are crucial to immunity to extracellular bacteria. The roles of these cells in the bovine species are poorly defined, because the characterization of bovine Th17 cells lags behind for want of straightforward cultivation and isolation procedures. We have developed procedures to differentiate, expand, and isolate bovine Th17 cells from circulating CD4+ T cells of adult cows. Using polyclonal stimulation with antibodies to CD3 and CD28, we expanded IL-17A-positive CD4+ T cells in a serum-free cell culture medium supplemented with TGF-β1, IL-6 and IL-2. Populations of CD4+ T cells producing IL-17A or IFN-γ or both cytokines were obtained. Isolation of IL-17A-secreting CD4+ T cells was performed by labelling surface IL-17A, followed by flow cytometry cell sorting. The sorted Th17 cells were restimulated and could be expanded for several weeks. These cells were further characterized by cytokine profiling at transcriptomic and protein levels. They produced high amounts of IL-17A and IL-17F, and moderate amounts of IL-22 and IFN-γ. The techniques developed will be useful to characterize the phenotypic and functional properties of bovine Th17 cells.

Neutralization of Interleukin-17A Attenuates Lipopolysaccharide-Induced Mastitis by Inhibiting Neutrophil Infiltration and the Inflammatory Response

Mastitis has been recognized as a common and major disease of cows with a strong impact on dairy farming. Interleukin-17A (IL-17A) has been shown to mediate crucial crosstalk between the immune system and various epithelial tissues, initiating a series of defensive mechanisms against bacterial and fungal infections. This crosstalk is especially involved in neutrophil infiltration. To evaluate the role of IL-17A in immune defense in the mammary gland in mice, we tested the effects of depleting IL-17A on changes in pathology, neutrophil infiltration, and pro-inflammatory cytokine levels in the mammary gland stimulated by lipopolysaccharide (LPS). Further, the effects of IL-17A on the activation of the nuclear factor-κB (NF-κB) signaling pathway during mastitis induced by LPS were also studied. The results showed that the production of IL-17A was significantly elevated during mastitis induced by LPS. IL-17A blockade via an intraperitoneal antibody injection protected against LPS-induced mastitis, as indicated by decreased neutrophil infiltration, myeloperoxidase activity, pro-inflammatory cytokines levels, and NF-κB signaling pathway molecule phosphorylation in response to LPS. In conclusion, an elevated IL-17 level plays a crucial role during mastitis, and anti-IL-17A antibody blockade protects against LPS-induced mammary gland inflammation induced through the NF-κB signaling pathway, which provides a new potential treatment target for mastitis.

Immunization of young heifers with staphylococcal immune evasion proteins before natural exposure to Staphylococcus aureus induces a humoral immune response in serum and milk

Background

Staphylococcus aureus, a leading cause of mastitis in dairy cattle, causes severe mastitis and/or chronic persistent infections with detrimental effects on the cows’ wellbeing, lifespan and milk production. Despite years of research there is no effective vaccine against S. aureus mastitis. Boosting of non-protective pre-existing immunity to S. aureus, induced by natural exposure to S. aureus, by vaccination may interfere with vaccine efficacy. The aim was to assess whether experimental immunization of S. aureus naïve animals results in an immune response that differs from immunity following natural exposure to S. aureus.

Results

First, to define the period during which calves are immunologically naïve for S. aureus, Efb, LukM, and whole-cell S. aureus specific serum antibodies were measured in a cohort of newborn calves by ELISA. Rising S. aureus specific antibodies indicated that from week 12 onward calves mounted an immune response to S. aureus due to natural exposure. Next, an experimental immunization trial was set up using 8-week-old heifer calves (n = 16), half of which were immunized with the immune evasion molecules Efb and LukM. Immunization was repeated after one year and before parturition and humoral and cellular immunity specific for Efb and LukM was determined throughout the study. Post-partum, antibody levels against LukM and EfB were significantly higher in serum, colostrum and milk in the experimentally immunized animals compared to animals naturally exposed to S. aureus. LukM specific IL17a responses were also significantly higher in the immunized cows post-partum.

Conclusions

Experimental immunization with staphylococcal immune evasion molecules starting before natural exposure resulted in significantly higher antibody levels against Efb and LukM around parturition in serum as well as the site of infection, i.e. in colostrum and milk, compared to natural exposure to S. aureus. This study showed that it is practically feasible to vaccinate S. aureus naïve cattle and that experimental immunization induced a humoral immune response that differed from that after natural exposure only.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1765-9) contains supplementary material, which is available to authorized users.

Identification of several key genes by microarray data analysis of bovine mammary gland epithelial cells challenged with Escherichia coli and Staphylococcus aureus

PURPOSE

This study was aimed at exploring the mechanisms and identifying the key candidate genes associated with S. aureus and E. coli mastitis.

METHODS

A public microarray dataset GSE24560 was downloaded. Differentially expressed genes (DEGs) were screened in E. coli- and S. aureus-infected primary bovine mammary gland epithelial cell (pBMEC) samples, and compared with control samples at 1 h, 6 h, and 24 h. A functional enrichment analysis was performed, and construction of a gene co-expression network was performed based on genes that showed consistent changes over time, which were identified using time series expression analysis. Then, a miRNA/TF regulatory network was constructed based on the genes in the co-expression network. The genes in the miRNA/TF regulatory network were screened for involvement in related diseases. Furthermore, the expression of several selected DEGs was further validated using real-time RT-PCR.

RESULTS

In total, 92 and 81 DEGs showed continuous differential expression over time in the E. coli- and S. aureus-inoculated groups. DEGs in the E. coli-inoculated group were associated with the RIG-I-like receptor signaling pathway, and those in the S. aureus-inoculated group were associated with the lysosome pathway. Time series expression analysis identified two gene clusters. NFKBIZ and GRO1 in the gene co-expression network were associated with inflammatory and defense responses. Moreover, several genes such as CXADR, APP, and CXCL2 in the miRNA/TF regulatory network, were associated with infection, inflammation, or stress-related diseases.

CONCLUSION

RIG-I like receptor pathway and several DEGs such as NFKBIZ, GRO1, CXCL2, and CXADR may play critical roles in the response to infection in pBMECs.

Application of pancreatic phospholipase A2 for treatment of bovine mastitis

Recent findings have indicated that secreted phospholipases A2 (sPLA2s) have anti-inflammatory functions, including relief of symptoms in a mouse model of mastitis. This prompted us to investigate the therapeutic application of sPLA2, PLA2G1B, for bovine mastitis. Initial testing of PLA2G1B's effect on bovine mammary epithelial cell (bMEC) line PS revealed no changes in cell viability or cytokine-secretion pattern. However, when cells were first treated with lipopolysaccharide endotoxin (LPS) or live bacteria (Escherichia coli or Staphylococcus aureus), incubation with PLA2G1B significantly improved cell viability, suggesting involvement of sPLA2s in protecting membranes from lipid-peroxidation damage, rather than a bactericidal action. When PLA2G1B was applied simultaneously with LPS, a significant short-term reduction in interleukin-8 secretion was observed compared with bMECs treated only with LPS, supporting previous reports that PLA2G1B affects interleukin-8 signaling in similar cells. Following the favorable outcome of the in vitro experiments, we tested PLA2G1B in vivo by mammary infusion into infected glands. In one of a small sample (n = 4) of lactating cows chronically infected with Streptococcus dysgalactiae, a single PLA2G1B treatment completely cleared inflammation and bacteria, demonstrating its potential to cure subclinical mastitis. PLA2G1B treatment did not affect coagulase-negative staphylococci infection. These types of mastitis may involve formation of a resistant biofilm, and its elimination may relate to sPLA2s' characteristic ability to aggregate with cellular debris, facilitating their internalization by macrophages. In a bovine model of clinical mastitis based on introduction of E. coli via the streak canal, a single mammary infusion of PLA2G1B led to faster recovery to pre-infection milk-yield levels and decrease of somatic cell counts. In this case, all of sPLA2s' modes of resolving inflammation may apply, including competitive binding of the sPLA2s’ receptor, the inactivation of which confers resistance to endotoxic shock. Hence, this study strongly supports further research into PLA2G1B as a cure for bovine mastitis.

Sensing of Escherichia coli and LPS by mammary epithelial cells is modulated by O-antigen chain and CD14

Escherichia coli is one of the major pathogens causing mastitis in dairy cattle. Yet, the factors which mediate the ability for E. coli to develop in the bovine mammary gland remain poorly elucidated. In a mouse model, infections induced by the reference mastitis E. coli P4 showed a strong colonisation of the mammary gland, while this strain had a low stimulating power on cells of the PS bovine mammary epithelial cell line. In order to understand if such a reduced response contributes to the severity of infection, a library of random mutants of P4 strain was screened to identify mutants inducing stronger response of PS cells. Among hyper-stimulating mutants, six were altered in genes involved in biosynthesis of lipopolysaccharide (LPS) and had lost their O-polysaccharide region, suggesting that the presence of O-antigen impairs the response of PS cells to LPS. Using purified smooth (S) and rough (R) fractions of LPS, we showed that the R-LPS fraction induced a stronger response from PS cells than the smooth LPS fraction. Biological activity of the S-LPS fraction could be restored by the addition of recombinant bovine CD14 (rbCD14), indicating a crucial role of CD14 in the recognition of S-LPS by Mammary Epithelial Cells (MEC). When S-LPS and R-LPS were injected in udder quarters of healthy lactating cows, an inflammation developed in all infused quarters, but the S-LPS induced a more intense pro-inflammatory response, possibly in relation to sizeable concentrations of CD14 in milk. Altogether, our results demonstrate that the O-antigen modulates the pro-inflammatory response of MEC to LPS, that S-LPS and R-LPS trigger different responses of MEC and that these responses depend on the presence of CD14.

Staphylococcus aureus Extracellular Vesicles Elicit an Immunostimulatory Response in vivo on the Murine Mammary Gland

Staphylococcus aureus is a major pathogen responsible for bovine mastitis, the most common and costly disease affecting dairy cattle. S. aureus naturally releases extracellular vesicles (EVs) during its growth. EVs play an important role in the bacteria-bacteria and bacteria-host interactions and are notably considered as nanocarriers that deliver virulence factors to the host tissues. Whether EVs play a role in a mastitis context is still unknown. In this work, we showed that S. aureus Newbould 305 (N305), a bovine mastitis isolate, has the ability to generate EVs in vitro with a designated protein content. Purified S. aureus N305-secreted EVs were not cytotoxic when tested in vitro on MAC-T and PS, two bovine mammary epithelial cell lines. However, they induced the gene expression of inflammatory cytokines at levels similar to those induced by live S. aureus N305. The in vivo immune response to purified S. aureus N305-secreted EVs was tested in a mouse model for bovine mastitis and their immunogenic effect was compared to that of live S. aureus N305, heat-killed S. aureus N305 and to S. aureus lipoteichoic acid (LTA). Clinical and histopathological signs were evaluated and pro-inflammatory and chemotactic cytokine levels were measured in the mammary gland 24 h post-inoculation. Live S. aureus induced a significantly stronger inflammatory response than that of any other condition tested. Nevertheless, S. aureus N305-secreted EVs induced a dose-dependent neutrophil recruitment and the production of a selected set of pro-inflammatory mediators as well as chemokines. This immune response elicited by intramammary S. aureus N305-secreted EVs was comparable to that of heat-killed S. aureus N305 and, partly, by LTA. These results demonstrated that S. aureus N305-secreted EVs induce a mild inflammatory response distinct from the live pathogen after intramammary injection. Overall, our combined in vitro and in vivo data suggest that EVs are worth to be investigated to better understand the S. aureus pathogenesis and are relevant tools to develop strategies against bovine S. aureus mastitis.

Lactobacillus casei BL23 modulates the innate immune response in Staphylococcus aureus-stimulated bovine mammary epithelial cells

Probiotics have been adopted to treat and prevent various diseases in humans and animals. They were notably shown to be a promising alternative to prevent mastitis in dairy cattle. This inflammation of the mammary gland is generally of infectious origin and generates extensive economic losses worldwide. In a previous study, we found that Lactobacillus casei BL23 was able to inhibit the internalisation of Staphylococcus aureus, one of the major pathogens involved in mastitis, into bovine mammary epithelial cells (bMEC). In this study, we further explored the capacity of this strain to modulate the innate immune response of bovine mammary epithelial cells during S. aureus infection. L. casei BL23 was able to decrease the expression of several pro-inflammatory cytokines, including interleukins 6, 8, 1α and 1β and tumour necrosis factor alpha, in S. aureus-stimulated bMEC, 8 h post-infection. On the other hand, L. casei did not impair the induction of defensins, such as lingual antimicrobial peptide and defensin β1 in the presence of S. aureus, and even slightly increased the induction of tracheal antimicrobial peptide during S. aureus infection. Finally, this strain did not alter the expression of the pattern recognition receptor nucleotide-binding oligomerisation domain proteins (NOD2). This study demonstrates that L. casei BL23 displayed anti-inflammatory properties on S. aureus-stimulated bMEC. These results open the way to further characterisation of the BL23 probiotic potential in a bovine mammary gland context and to a better understanding of how all these beneficial properties combine in vivo to combat mastitis pathogens.

Immunomodulation of Host Chitinase 3-Like 1 During a Mammary Pathogenic Escherichia coli Infection

Chitin is a N-acetyl-d-glucosamine biopolymer that can be recognized by chitin-binding proteins. Although mammals lack chitin synthase, they induce proteins responsible for detecting chitin in response to bacterial infections. Our aim was to investigate whether chitinase 3-like 1 (CHI3L1) has a potential role in the innate immunity of the Escherichia coli (E. coli) infected mammary gland. CHI3L1 protein was found to be secreted in whey of naturally coliform-affected quarters compared to whey samples isolated from healthy udders. In addition, gene expression of CHI3L1 was confirmed in udder tissue of cows experimentally infected with a mammary pathogenic E. coli (MPEC) strain. Despite the known anatomical differences, the bovine udders’ innate immune response was mimicked by applying an experimental mouse model using MPEC or non-MPEC isolates. The effect of CHI3L1 expression in the murine mammary gland in response to coliform bacteria was investigated through the use of CHI3L1^−/− mice as well as through treatment with either a pan-caspase inhibitor or chitin particles in wild-type mice. The local induction of CHI3L1 postinfection with different E. coli strains was demonstrated to be independent of both bacterial growth and mammary interleukin (IL)-8 levels. Indeed, CHI3L1 emerged as a regulator impacting on the transcytosis of Ly6G-positive cells from the interstitial space into the alveolar lumen of the mammary tissue. Furthermore, CHI3L1 was found to be upstream regulated by caspase activity and had a major downstream effect on the local pro-inflammatory cytokine profile, including IL-1beta, IL-6, and RANTES/CCL5. In conclusion, CHI3L1 was demonstrated to play a key role in the cytokine and caspase signaling during E. coli triggered inflammation of the mammary gland.

Pathogen-specific responses in the bovine udder. Models and immunoprophylactic concepts

Bovine mastitis is a disease of major economic effects on the dairy industry worldwide. Experimental in vivo infection models have been widely proven as an effective tool for the investigation of pathogen-specific host immune responses. Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) are two common mastitis pathogens with an opposite clinical outcome of the disease. E. coli and S. aureus have proven to be valid surrogates to model clinical and subclinical mastitis respectively. Contemporary transcriptome profiling studies demonstrated that the transcriptomic response in the teat reflects the course of pathogen-specific mastitis, being ultimately determined by the immune response of the mammary epithelial cells. After an experimental in vivo challenge, E. coli induces a vigorous early transcriptional response in udder tissue being quantitatively and - notably - qualitatively distinct from the much weaker response against an S. aureus infection. E. coli mastitis models proved that the local response in the infected udder quarters is accompanied by a response in non-infected neighbouring udder quarters modulating systemically their immune responsiveness. Immunomodulation of the udder was investigated in animal models. Pathophysiological consequences were studied after intramammary administration of cytokines, chemokines, growth factors, steroidal anti-inflammatory drugs, or priming of tissue resident cells with pathogen-derived molecules. The latter approaches resulted only in a temporal protection of the udder, reducing transiently the risk of infection but sustained lowering of the severity of an eventually occurring mastitis. They offer an alternative to vaccination trials, which over decades also did not yield protection against new infections.

Cellular and humoral immune response to recombinant Escherichia coli OmpA in cows

The outer membrane protein (Omp) A is a major constituent of the outer membrane of Escherichia coli. This protein has been used in several vaccine development studies, but seldom with a view to vaccinating against mastitis. The objective of this study was to investigate the immunogenicity of E. coli OmpA and its vaccine potential for cows. Both the humoral and cellular immune responses were investigated. The gene for OmpA of the mastitis-causing strain P4 was cloned and expressed, and the recombinant protein (rEcOmpA) purified. Cows were immunized twice with rEcOmpA with adjuvant one month apart by the systemic route. Before immunization, few antibodies to rEcOmpA were detected, and there was little production of IL-17A in a whole blood stimulation assay (WBA) with rEcOmpA. Antibodies to rEcOmpA were induced by immunization. These antibodies were not able to react with E. coli P4, but reacted with a rough P4 mutant prepared by inactivating the rfb locus. This suggests that the complete LPS O-chain precluded the accessibility of antibodies to their target at the outer membrane. The cellular immune response appeared to be biased towards a Th17-type, as more IL-17A than IFN-γ was produced in the OmpA-specific WBA. There was a good correlation between antibody titers and the production of IL-17A in the WBA. The intramammary instillation of rEcOmpA elicited a slight local inflammatory response which was not related to the WBA. Overall, the interest of OmpA as vaccine immunogen was not established, although other experimental conditions (dose, adjuvant, route) need to be investigated to conclude definitively. The study pointed to several important issues such as the accessibility of OmpA to antibodies and the weakness of Th1-type response induced by OmpA.

Comparison of the immune responses associated with experimental bovine mastitis caused by different strains of Escherichia coli

We studied the mammary immune response to different mammary pathogenic Escherichia coli (MPEC) strains in cows, hypothesising that the dynamics of response would differ. E. coli is a major aetiologic agent of acute clinical bovine mastitis of various degrees of severity with specific strains being associated with persistent infections. We compared challenge with three distinct pathogenic MPEC strains (VL2874, VL2732 and P4), isolated from different forms of mastitis (per-acute, persistent and acute, respectively). A secondary objective was to verify the lack of mammary pathogenicity of an environmental isolate (K71) that is used for comparison against MPEC in genomic and phenotypic studies. Twelve cows were challenged by intra-mammary infusion with one of the strains. Cellular and chemokine responses and bacterial culture follow-up were performed for 35 d. All cows challenged by any of the MPEC strains developed clinical mastitis. Differences were found in the intensity and duration of response, in somatic cell count, secreted cytokines (TNF-α, IL-6 and IL-17) and levels of milk leucocyte membrane Toll-like receptor 4 (TLR4). A sharp decrease of TLR4 on leucocytes was observed concomitantly to peak bacterial counts in milk. Intra-mammary infusion of strain K71 did not elicit inflammation and bacteria were not recovered from milk. Results suggest some differences in the mammary immune response to distinct MPEC strains that could be correlated to their previously observed pathogenic traits. This is also the first report of an E. coli strain that is non-pathogenic to the bovine mammary gland.

Escherichia coli mastitis strains: In vitro phenotypes and severity of infection in vivo

Mastitis remains a major infection of dairy cows and an important issue for dairy farmers and the dairy industry, in particular infections due to Escherichia coli strains. So far, properties specific to E. coli causing mastitis remain ill defined. In an attempt to better understand the properties required for E. coli to trigger mastitis, we used a range of in vitro assays to phenotypically characterize four E. coli strains, including the prototypical E. coli mastitis strain P4, possessing different relative abilities to cause mastitis in a mouse model. Our results indicate that a certain level of serum resistance might be required for colonization of the mammary gland. Resistance to neutrophil killing is also likely to contribute to a slower clearance of bacteria and higher chances to colonize the udder. In addition, we show that the four different strains do induce a pro-inflammatory response by mammary epithelial cells but with different intensities. Interestingly, the prototypical mastitis strain P4 actually induces the less intense response while it is responsible for the most severe infections in vivo. Altogether, our results suggest that different strategies can be used by E. coli strains to colonize the mammary gland and cause mastitis.

Interleukins and large domestic animals, a bibliometric analysis

Interleukins have been well described in mice and humans. In large domestic animals the situation is drastically different and there is still a need for further researches aiming at identifying all the homologous interleukins and comparing their functions among species. We performed here a bibliometric analysis of all interleukins described in the literature in various large animal species to identify what is known so far and to underline where there is a need for new studies. Using indicators such as H index but also M quotient, A index, G index, GH ratio, and HG index we ranked 39 interleukins identified so far in bovine, caprine, equine, ovine, and porcine, the main large domestic animals. Indexes and ratio under investigations were higher for IL1, IL2, IL4, IL5, IL6, IL8, IL10, IL12, and IL18 than for other interleukins, particularly in bovine and porcine species and to a certain extent in equine species. Recently discovered interleukins presented low values for the different indexes, quotient, and ratio. Even some “old” interleukins showed low values highlighting the need for further developments in comparative immunology. For instance an interleukin such as IL4 demonstrated variation in its functions between species. In conclusion, this study provides the first bibliometric analysis dedicated to large domestic animal interleukins and underlines the need for more studies to fully determine the structure and the functions of interleukins in other mammal species.

Permissiveness of bovine epithelial cells from lung, intestine, placenta and udder for infection with Coxiella burnetii

Ruminants are the main source of human infections with the obligate intracellular bacterium Coxiella (C.) burnetii. Infected animals shed high numbers of C. burnetii by milk, feces, and birth products. In goats, shedding by the latter route coincides with C. burnetii replication in epithelial (trophoblast) cells of the placenta, which led us to hypothesize that epithelial cells are generally implicated in replication and shedding of C. burnetii. We therefore aimed at analyzing the interactions of C. burnetii with epithelial cells of the bovine host (1) at the entry site (lung epithelium) which govern host immune responses and (2) in epithelial cells of gut, udder and placenta decisive for the quantity of pathogen excretion. Epithelial cell lines [PS (udder), FKD-R 971 (small intestine), BCEC (maternal placenta), F3 (fetal placenta), BEL-26 (lung)] were inoculated with C. burnetii strains Nine Mile I (NMI) and NMII at different cultivation conditions. The cell lines exhibited different permissiveness for C. burnetii. While maintaining cell viability, udder cells allowed the highest replication rates with formation of large cell-filling Coxiella containing vacuoles. Intestinal cells showed an enhanced susceptibility to invasion but supported C. burnetii replication only at intermediate levels. Lung and placental cells also internalized the bacteria but in strikingly smaller numbers. In any of the epithelial cells, both Coxiella strains failed to trigger a substantial IL-1β, IL-6 and TNF-α response. Epithelial cells, with mammary epithelial cells in particular, may therefore serve as a niche for C. burnetii replication in vivo without alerting the host’s immune response.

Enhancing the toolbox to study IL-17A in cattle and sheep

The development of methods to detect cytokine expression by T cell subsets in ruminants is fundamental to strategic development of new livestock vaccines for prevention of infectious diseases. It has been possible to detect T cell expression of IFN-γ, IL-4 and IL-10 in ruminants for many years but methods to detect expression of IL-17A are relatively limited. To address this gap in capability we have cloned bovine and ovine IL-17A cDNAs and expressed biologically-active recombinant proteins in Chinese Hamster Ovary (CHO) cells. We used the transfected CHO cells to screen commercially-available antibodies for their ability to detect IL-17A expression intracellularly and in culture supernates. We demonstrate that an ELISA for bovine IL-17A detects native ovine IL-17A. Moreover, the constituent polyclonal antibodies (pabs) in the ELISA were used to enumerate peripheral blood mononuclear cells (PBMC) expressing IL-17A from cattle and sheep by ELISpot. We identified two monoclonal antibodies (mabs) that detect recombinant intracellular IL-17A in CHO cells by flow cytometry. One of these mabs was used to detect native intracellular IL-17A expression in PBMC in conjunction with cell surface phenotyping mabs [CD4+ve, CD8+ve and Workshop Cluster 1 (WC-1)+ve gamma-delta (γδ)] we show that distinct T cell subsets in cattle (defined as CD4+ve, CD8+ve or WC-1+ve) and sheep (defined as CD4+ve or WC-1+ve) can express IL-17A following activation. These novel techniques provide a solid basis to investigate IL-17A expression and define specific CD4+ve T cell subset activation in ruminants.

Staphylococcus aureus Phenol-Soluble Modulins Impair Interleukin Expression in Bovine Mammary Epithelial Cells

The role of the recently described interleukin-32 (IL-32) in Staphylococcus aureus-induced mastitis, an inflammation of the mammary gland, is unclear. We determined expression of IL-32, IL-6, and IL-8 in S. aureus- and Escherichia coli-infected bovine mammary gland epithelial cells. Using live bacteria, we found that in S. aureus-infected cells, induction of IL-6 and IL-8 expression was less pronounced than in E. coli-infected cells. Notably, IL-32 expression was decreased in S. aureus-infected cells, while it was increased in E. coli-infected cells. We identified the staphylococcal phenol-soluble modulin (PSM) peptides as key contributors to these effects, as IL-32, IL-6, and IL-8 expression by epithelial cells exposed to psm mutant strains was significantly increased compared to that in cells exposed to the isogenic S. aureus wild-type strain, indicating that PSMs inhibit the production of these interleukins. The use of genetically complemented strains confirmed this observation. Inasmuch as the decreased expression of IL-32, which is involved in dendritic cell maturation, impairs immune responses, our results support a PSM-dependent mechanism that allows for the development of chronic S. aureus-related mastitis.

Innate and Adaptive Immunity Synergize to Trigger Inflammation in the Mammary Gland

The mammary gland is able to detect and react to bacterial intrusion through innate immunity mechanisms, but mammary inflammation can also result from antigen-specific adaptive immunity. We postulated that innate and adaptive immune responses could synergize to trigger inflammation in the mammary gland. To test this hypothesis, we immunized cows with the model antigen ovalbumin and challenged the sensitized animals with either Escherichia coli lipopolysaccharide (LPS) as innate immunity agonist, ovalbumin as adaptive immunity agonist, or both agonists in three different udder quarters of lactating cows. There was a significant amplification of the initial milk leukocytosis in the quarters challenged with the two agonists compared to leukocytosis in quarters challenged with LPS or ovalbumin alone. This synergistic response occurred only with the cows that developed the ovalbumin-specific inflammatory response, and there were significant correlations between milk leukocytosis and production of IL-17A and IFN-γ in a whole-blood ovalbumin stimulation assay. The antigen-specific response induced substantial concentrations of IL-17A and IFN-γ in milk contrary to the response to LPS. Such a synergy at the onset of the reaction of the mammary gland suggests that induction of antigen-specific immune response with bacterial antigens could improve the initial immune response to infection, hence reducing the bacterial load and contributing to protection.

Lactic Acid Bacteria Isolated from Bovine Mammary Microbiota: Potential Allies against Bovine Mastitis

Bovine mastitis is a costly disease in dairy cattle worldwide. As of yet, the control of bovine mastitis is mostly based on prevention by thorough hygienic procedures during milking. Additional strategies include vaccination and utilization of antibiotics. Despite these measures, mastitis is not fully under control, thus prompting the need for alternative strategies. The goal of this study was to isolate autochthonous lactic acid bacteria (LAB) from bovine mammary microbiota that exhibit beneficial properties that could be used for mastitis prevention and/or treatment. Sampling of the teat canal led to the isolation of 165 isolates, among which a selection of ten non-redundant LAB strains belonging to the genera Lactobacillus and Lactococcus were further characterized with regard to several properties: surface properties (hydrophobicity, autoaggregation); inhibition potential of three main mastitis pathogens, Staphylococcus aureus, Escherichia coli and Streptococcus uberis; colonization capacities of bovine mammary epithelial cells (bMEC); and immunomodulation properties. Three strains, Lactobacillus brevis 1595 and 1597 and Lactobacillus plantarum 1610, showed high colonization capacities and a medium surface hydrophobicity. These strains are good candidates to compete with pathogens for mammary gland colonization. Moreover, nine strains exhibited anti-inflammatory properties, as illustrated by the lower IL-8 secretion by E. coli-stimulated bMEC in the presence of these LAB. Full genome sequencing of five candidate strains allowed to check for undesirable genetic elements such as antibiotic resistance genes and to identify potential bacterial determinants involved in the beneficial properties. This large screening of beneficial properties while checking for undesirable genetic markers allowed the selection of promising candidate LAB strains from bovine mammary microbiota for the prevention and/or treatment of bovine mastitis.

IL-17A Is an Important Effector of the Immune Response of the Mammary Gland to Escherichia coli Infection

The cytokine IL-17A has been shown to play critical roles in host defense against bacterial and fungal infections at different epithelial sites, but its role in the defense of the mammary gland (MG) has seldom been investigated, although infections of the MG constitute the main pathology afflicting dairy cows. In this study, we showed that IL-17A contributes to the defense of the MG against Escherichia coli infection by using a mouse mastitis model. After inoculation of the MG with a mastitis-causing E. coli strain, the bacterial load increased rapidly, triggering an intense influx of leukocytes into mammary tissue and increased concentrations of IL-6, IL-22, TNF-α, and IL-10. Neutrophils were the first cells that migrated intensely to the mammary tissue, in line with an early production of CXCL2. Depletion of neutrophils induced an increased mammary bacterial load. There was a significant increase of IL-17-containing CD4(+) αβ T lymphocyte numbers in infected glands. Depletion of IL-17A correlated with an increased bacterial colonization and IL-10 production. Intramammary infusion of IL-17A at the onset of infection was associated with markedly decreased bacterial numbers, decreased IL-10 production, and increased neutrophil recruitment. Depletion of CD25(+) regulatory T cells correlated with a decreased production of IL-10 and a reduced bacterial load. These results indicate that IL-17A is an important effector of MG immunity to E. coli and suggest that an early increased local production of IL-17A would improve the outcome of infection. These findings point to a new lead to the development of vaccines against mastitis.

Antigen-Specific Mammary Inflammation Depends on the Production of IL-17A and IFN-γ by Bovine CD4+ T Lymphocytes

Intramammary infusion of the antigen used to sensitize cows by the systemic route induces a local inflammation associated with neutrophil recruitment. We hypothesize that this form of delayed type hypersensitivity, which may occur naturally during infections or could be induced intentionally by vaccination, can impact the outcome of mammary gland infections. We immunized cows with ovalbumin to identify immunological correlates of antigen-specific mammary inflammation. Intraluminal injection of ovalbumin induced a mastitis characterized by a prompt tissue reaction (increase in teat wall thickness) and an intense influx of leukocytes into milk of 10 responder cows out of 14 immunized animals. The magnitude of the local inflammatory reaction, assessed through milk leukocytosis, correlated with antibody titers, skin thickness test, and production of IL-17A and IFN-γ in a whole-blood antigen stimulation assay (WBA). The production of these two cytokines significantly correlated with the magnitude of the milk leukocytosis following the ovalbumin intramammary challenge. The IL-17A and IFN-γ production in the WBA was dependent on the presence of CD4+ cells in blood samples. In vitro stimulation of peripheral blood lymphocytes with ovalbumin followed by stimulation with PMA/ionomycin allowed the identification by flow cytometry of CD4+ T cells producing either IL-17A, IFN-γ, or both cytokines. The results indicate that the antigen-specific WBA, and specifically IL-17A and IFN-γ production by circulating CD4+ cells, can be used as a predictor of mammary hypersensitivity to protein antigens. This prompts further studies aiming at determining how Th17 and/or Th1 lymphocytes modulate the immune response of the mammary gland to infection.