DIMINISHED MAMMARY-GLAND LYMPHOCYTE FUNCTIONS PARALLEL SHIFTS IN TRAFFICKING PATTERNS DURING THE POSTPARTUM PERIOD

Once activated, lymphocytes can regulate both specific and nonspecific immune responses. Alterations in lymphocyte function may increase the host's vulnerability to bacterial infections such as mastitis. Suscep tibility to mastitis as well as diminished leukocyte functional capabi lities have been shown to be influenced by lactational stage. Therefor e, the present study characterized the phenotypes and functions of sev eral bovine lymphoid populations at two points in the lactational cycl e, Mononuclear cells were isolated from peripheral blood, supramammary lymph nodes, and mammary parenchyma of mid-lactating and postpartum d airy cows. The phenotypic composition, proliferative ability, cytokine secretion, and cytotoxic activity of isolated leukocytes were assesse d with respect to lactational stage and tissue source. Lower percentag es of T lymphocytes were consistent with diminished mitogen-stimulated proliferation and spontaneous cytotoxic activity by lymphocytes isola ted from postpartum compared with mid-lactating animals. Stimulation w ith interteukin-2 did not enhance the cytotoxic activity or proliferat ive ability of lymphocytes isolated postpartum to similar levels obser ved for those isolated from mid-lactating animals. These data indicate that certain diminished lymphocyte functions observed during the post partum period may result from shifts in leukocyte trafficking patterns .