Innate immune response of mammary gland epithelial cells to intracellular Staphylococcus aureus

Background. Non-specific (innate) immune response plays a major role in defending udder from bacteria invasion. Innate soluble immune defenses are all involved in preventing bacteria adhesion, multiplication and in bacteria killing. Recent investigations suggested that epithelial cells could have a large and important role as a source for soluble components of immune defenses's. Methods. Ten S.aureus isolates from subclinical mastitis cases in dairy cows of different herds were considered. These isolates were characterized by different virulence genes patterns. A clonal cell line established from udder epithelial cells (BME-UV), synthesizing several milk components, was used as an in vitro model. Cell line was exposed to S.aureus and the intracellular and extracellular release of Lysozyme and NAGase were assessed from 4 h until 24 h by a fluorescence-based procedure on a microplate fluorimeter. Results. The preliminary results of this study showed that S.aureus strains invading epithelial cells elicited an immunological response with levels related to strain characteristics. The pattern of lysozyme concentration was time-dependent and showed an extracellular increase at 24h after exposure to S.aureus. Moreover, it was detectable intracellularly starting at 4h, but not in the surnatant before 24 h. NAGase is a glycosidase and showed a release pattern different from lysozyme, even if it is also considered a lysosomial enzyme. Its extracellular concentration increased at 24h, when cells showed dysfunction, but at cell level it decreased over the 24 h. Conclusions. These data confirms that epithelial cells could play an important role in udder innate defenses. Moreover, they suggest that the release pattern of the two enzymes considered is different. Lysozyme is involved in antibacterial activity and could be considered as a marker of bacteria-induced inflammation. About NAGase, it could be hypotesized that it is more a marker of cellular damage and an extracellular increase is a sign of cellular dysfunction and/or disruption rather than of inflammation.