Abstract
Mastitis remains a major disease of cattle with a strong impact on the dairy industry. There is a growing interest in understanding how cell mediated immunity contributes to the defence of the mammary gland against invading mastitis causing bacteria. Cytokines belonging to the IL-17 family, and the cells that produce them, have been described as important modulators of the innate immunity, in particular that of epithelial cells. We report here that expression of IL-17A and IL-17F genes, encoding two members of the IL-17 family, are induced in udder tissues of cows experimentally infected with Escherichia coli. The impact of IL-17A on the innate response of bovine mammary epithelial cells was investigated using a newly isolated cell line, the PS cell line. We first showed that PS cells, similar to primary bovine mammary epithelial cells, were able to respond to agonists of TLR2 and to LPS, provided CD14 was added to the culture medium. We then showed that secretion of CXCL8 and transcription of innate immunity related-genes by PS cells were increased by IL-17A, in particular when these cells were stimulated with live E. coli bacteria. Together with data from the literature, these results support the hypothesis that IL-17A and IL-17 F could play an important role in mediating of host-pathogen interactions during mastitis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0201-4) contains supplementary material, which is available to authorized users.
Highlights
Despite decades of research, mastitis remains a major concern in dairy farming
IL-17A and IL-17 F gene expression is induced upon infection of the udder by E. coli Previous reports showed that experimental intramammary inoculation of Escherichia coli 1303 induced a significant host response [25]
Expression of IL-17A and IL-17F was significantly increased in E. coli infected quarters, compared to non-infected quarters (Figures 1C and D): the mean fold-change for IL-17A was 72 in samples from cows infected by E. coli
Summary
Mastitis remains a major concern in dairy farming. Mastitis are mainly due to bacterial infections (Gram-positive pathogens such as Staphylococcus aureus and Streptococcus uberis, or Gram-negative pathogens such as Escherichia coli) [1].Previous studies have allowed the identification of key molecular events that lead to the recruitment of neutrophils in the mammary gland upon bacterial colonization. Production of pro-inflammatory cytokines such as IL-1β, IL-6 and TNF-α and the chemokine CXCL8 have been detected in milk from clinically affected animals and are supposed to contribute to the inflammation observed in mastitis [2,4]. In vivo experiments indicate that the severity of E. coli mastitis mainly depends on host factors and that a quick and efficient response is important for an efficient clearance of the bacteria [5]. This process relies heavily on the recruitment of neutrophils during infection: a delay in the recruitment of neutrophils aggravates the infection [6,7]. It is expected that any mechanism that modulates the immune response of the host could participate in the defence against E. coli mastitis
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