Effect of chronic staphylococcal mastitis on mitogenic responses of bovine lymphocytes.

We compared mitogenic responses of milk and peripheral blood lymphocytes from nonmastitic (control) cows and cows with experimentally induced staphylococcal mastitis in one gland. Milk lymphocytes from infected glands were essentially unresponsive to Concanavalin A, phytohemagglutinin-P, and pokeweed mitogen. Proliferative responses of milk lymphocytes from uninfected glands of infected cows were not as depressed as those from infected glands but were significantly less than those of milk lymphocytes from control cows. Proliferative responses of peripheral blood lymphocytes from control and infected cows to Concanavalin A and phytohemagglutinin-P were similar; however, peripheral blood lymphocytes from infected cows responded in reduced fashion to pokeweed mitogen compared with peripheral blood lymphocytes from control animals. These observations demonstrate that in vitro lymphocyte blastogenesis is markedly depressed during infection, suggesting that in vivo lymphocyte function is compromised, possibly contributing to the chronicity of staphylococcal mastitis.