Bovine milk immunoglobulin A and immunoglobulin G inhibit the adhesion of Staphylococcus aureus to bovine mammary epithelial cells

Mastitis is a widespread and severe disease that affects the dairy industry. Bacterial adhesion to the bovine mammary epithelium is a critical first step in the pathogenesis of Staphylococcus aureus-induced mastitis. Immunoglobulins play an important role in the adaptive immune system. Bovine milk contains both IgA and IgG. Substantial knowledge of the antiadhesive effects of bovine milk IgA and IgG against S. aureus in bovine mammary epithelial cells (BMEC) is required to develop effective vaccines against mastitis. In this study, we purified IgA and IgG from bovine milk and examined their antiadhesive effects on S. aureus isolated from bovine clinical mastitis to mammary epithelium using cultured BMEC. The molecular weights of bovine milk IgA and bovine milk IgG are approximately 380 and 100 to 140 kDa, respectively, under nonreducing conditions. In addition, the binding ability of milk IgA to S. aureus lysate was higher than that of milk IgG. Furthermore, both bovine milk IgA and IgG exhibited antiadhesive effects against S. aureus on BMEC, whereas higher antiadhesive effects on S. aureus were observed for bovine milk IgA than for milk IgG at the same protein amount. These findings demonstrate that milk IgA has a stronger antiadhesive effect on S. aureus binding to BMEC than IgG, possibly due to its dimeric structure and higher binding ability. Our findings may contribute to the development of effective vaccines for mastitis.