Infections of the bovine mammary gland are, in addition to the affliction of the animals, a great economic burden in the dairy industry. A better understanding of the innate immune response of the host could lead to a better selection of mastitis resistant cows or to better prophylactic and therapeutical treatments. The objective of the present study was to investigate the involvement of the epithelial cells into the outcome of mastitis induced by different pathogens. Primary epithelial cell cultures isolated from milk of Brown swiss cows and coloured german goats, and tissue of cows were used to test the immune response. Because the cells of the cows showed different responses to isolated bacterial endotoxins (lipopolysaccharide, lipoteichoic acid, and peptidoglycans) compared to whole bacteria, they were treated with heat inactivated (10 MOI) gram-negative Escherichia coli (E.coli), a very common pathogen causing acute and severe intra-mammary infections, with Staphylococcus aureus (S.aureus) and coagulase-negative Staphylococcus (CNS), both prevalent cause of chronic and subclinical, and, Streptococcus uberis (Str.uberis) an inducer of acute and chronic mastitis. Goat cells were treated with 10 MOI heat inactivated S.aureus causing in opposite to cows an acute, clinical mastitis and LPS. In cows E.coli induced an increased mRNA expression of interleukin-(IL) 8, IL-6, tumor necrosis factor alpha (TNF) and granulozytes, macrophage-stimulating factor (GM-CSF) within a 30 min treatment. IL-8, IL-6 and TNF mRNA levels were still elevated after 60 min, 90 min, 6 h and 24 h. After 6 h S.aureus induced an increase in mRNA expression of IL-6, IL-8, TNF and SAA. After a 24 h treatment the expression of these immunomodulators was still elevated. Interestingly, Str.uberis in the same concentration did only induce the mRNA expression of GM-CSF after 60 min and the IL-8 after a 6 h treatment but had no influence on other immunomodulator mRNA expression. CNS treated cells needed a MOI of 50 for any reaction. This MOI induced a reaction on mRNA levels of IL-6 and IL-8 but not on TNF after 6 h. In goats S.aureus induced an increase in mRNA expression of IL-8 and TNF after 1 and 6 h. After a 24 h treatment just the mRNA level of TNF was elevated.

In conclusion mammary gland epithelial cells are involved in the different immune response to various mastitis pathogens. In cows, E.coli always induced an earlier immune response compared to S.aureus. This pathogen induced a later and probably for the immne system weaker reaction, not strong enough to cause an acute intramammary infection. Str.uberis in the same concentration induced only an increased GM-CSF and IL-8 mRNA expression after a 60 min or a 6 h treatment, respectively. This bacterium probably stimulates different immune relevant gene expressions not measured here or does not stimulate the mammary gland epithelial cells. The cells needed a 5-fold higher dose of KNS to respond with induced mRNA levels of IL-6 and TNF but not IL-8. KNS maybe does not stimulate the immune system enough to induce an acute mastitis and is like by the epithelial cells just recognized in very high dosis. IL-8 plays an important role as a chemotactic stimulus that is missing here. Goat mammary gland epithelial cells showed a early increase of IL-8 and TNF, that could be high enough, combined with the response of the immune cells in the milk, to induce an acute and severe intra-mammary infection.