Bovine mammary gland epithelial cells innate immune response to S. Aureus

Recently, epithelial cells (EC) has been recognized as a major source of innate immune components useful to protect mammary gland from infections. A study was designed to investigate the response induced by different S.aureus strains on EC. Ten S.aureus isolated from subclinical mastitis cases in dairy cows of different herds were selected based on their genetic characteristics and antimicrobial susceptibility. A clonal cell line (BME-UV) established from udder primary epithelial cell synthesizing several milk components was used as an in vitro model. Previous studies showed that this cell line can express several cytokines and immune components when stimulated by bacteria or toxins. Bacteria count, lysozyme (LYZ) and NAGase (NAG) concentration were used to assess cellular response, while the strains were classified in two groups by TLR expression: high rate (HR) and low rate (LR). As expected S.aureus growth both intracellularly and extracellularly. However, extracellular S.aureus showed similar curves when isolates expressing TLRs in high rate and in low rate were considered, while intracellular curves were different. Indeed, in this latter case LR isolates peaked at 10 h PI, then the concentration decreased, while increased around 2 logs in the HR group. The results of the study confirmed the capability of EC to produce component of innate immunity. However the response was triggered only when bacteria concentration was over 0.5 log10 µg/ml. When LYZ concentration in relation to TLR expression was considered, data showed as extracellular LYZ increased more rapidly in HR than in LR isolates until 10h PI, when the two curves stated to overlap. Intracellular LYZ concentration showed to have a very similar pattern both in HR and LR groups. However, LYZ level were always higher in HR group when compared with LR one. Extracellular NAG was always very low, while intracellular NAG concentrations were higher than extracellular ones, as expected. Also when TLR expression were considered, a similar pattern for both LR and HR isolates were observed, even if at different mean levels up 10 h PI. Then, the concentration decreased at intracellular level and increased extracellularly. S.aureus to have different capability to induce innate immune response. However, these difference were influenced by the growth rate and by the site of infection (intracellular/extracellular). The production of innate immune parameters from EC in response to S.aureus infections suggest that these cells could be a target of choice in developing immune-modulators to be used to control bovine mastitis