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International audience; 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.

International audience; Interleukin 17A-producing T helper cells (Th17) are effector memory CD4+ T cells that are crucial to adaptive immunity to extracellular bacteria. The activities of these cells in the bovine species are not yet defined for want of straightforward cultivation and isolation procedures. We have developed a method to cultivate, expand, sort and maintain in culture bovine Th17 cells from circulating CD4+ T cells of adult cows. Using polyclonal stimulation (antibodies to CD3 and CD28), we expanded positive CD4+ IL-17A+ T (Th17) cells in a cell culture medium without serum supplemented with TGF-β1 and IL-6. We used IL-2 to expand the cells, which were characterized by intracellular labeling for IL-17A and IFN-γ. Then, we isolated populations of CD4+ T cells producing IL-17A, IFN-γ or both by labeling surface IL-17A with either a complex of biotinylated anti-CD45 antibodies-streptavidin-biotinylated anti-IL-17A antibodies or by direct surface labeling with antibodies to IL-17A, followed by flow cytometry cell sorting. The percentages of surface-labeled IL-17A-secreting cells were quite similar to the percentages of intracellular-labeled IL-17A-producing cells of the same cultures, and the two labeling procedures of live cells yielded similar results. The sorted IL-17A+ cells were restimulated and expanded. After expansion, 80% of the isolated Th17 cells were positive for IL-17A intracellular labeling. The sorted IL-17A+ cells can be frozen, stored and expanded again. The sorted Th17 cells secreted much more IL-17A and IL-17F than did CD4+ IL-17- cells. Notably, most of Th17 cells secreted IFN-γ, although in lower amounts than did CD4+ IL-17- cells. Sorted cells were characterized by transcriptomic profiling. Genes coding for Th17 signature cytokines (IL-17A, IL-17F, IL-26) and transcription factors (RORγt, RORa) were overexpressed in Th17 cells. The techniques developed will make it possible to investigate the phenotypic and functional profiles of bovine Th17 cells along with their stability or plasticity.

International audience

International audience

Staphylococcus aureus is the major cause of very severe mastitis of dairy goats. The initial objective of our study was to fine-tune an experimental model of infection of the goat mammary gland with two strains of S. aureus and two lines of goats (low and high somatic cell score lines). Following the challenge, the 10 infected goats divided in two clear-cut severity groups, independently of the S. aureus strain and the goat line. Five goats developed very severe mastitis (of which four were gangrenous) characterized by uncontrolled infection (UI group), whereas the other five kept the infection under control (CI group). The outcome of the infection was determined by 18 h post-infection (hpi), as heralded by the bacterial milk concentration at 18 hpi: more than 107/mL in the UI group, about 106/mL in the CI group. Leukocyte recruitment and composition did not differ between the groups, but the phagocytic killing at 18 hpi efficiency did. Contributing factors involved milk concentrations of α-toxin and LukMF′ leukotoxin, but not early expression of the genes encoding the pentraxin PTX3, the cytokines IL-1α and IL-1β, and the chemokines IL-8 and CCL5. Concentrations of TNF-α, IFN-γ, IL-17A, and IL-22 rose sharply in the milk of UI goats when infection was out of control. The results indicate that defenses mobilized by the mammary gland at an early stage of infection were essential to prevent staphylococci from reaching critical concentrations. Staphylococcal exotoxin production appeared to be a consequent event inducing the evolution to gangrenous mastitis. Electronic supplementary material The online version of this article (10.1186/s13567-018-0564-4) contains supplementary material, which is available to authorized users.

International audience; 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.