Enhancing bactericidal activity of bovine lymphoid cells during the periparturient period

The antibacterial activity of bovine lymphocytes was evaluated following in vitro stimulation with interleukin-2. Mononuclear cells were isolated from the blood, lymph node, and mammary parenchymal tissue of four lactating and four periparturient dairy cows. These cells were evaluated for antibacterial activity against Staphylococcus aureus following incubation for 48 h with or without interleukin-2. Cultures stimulated with interleukin-2 had higher bactericidal activity of all three isolated cell populations than did unstimulated cultures, regardless of lactational stage. This observation suggests that this effector function may possibly be activated in vivo and may potentially increase mammary gland resistance to bacterial infections during periods of increased susceptibility. Flow cytometric analysis of the cultured cells revealed that antibacterial effector cells were mainly CD2+ and were depleted of macrophages. Despite shifts in CD4+, CD8+, and gamma delta T lymphocytes during the periparturient period, bactericidal activity was similar among the three cell sources. This similarity suggests that these lymphocyte phenotypes might not be directly responsible for this effector function. Identification of the antibacterial effector phenotype and its mechanism of action may lead to immunoregulatory strategies aimed at enhancing this novel bactericidal function.