Longitudinal study of lymphocyte subsets and major histocompatibility complex-class II expressing cells in mammary glands of sows.

OBJECTIVE: To determine whether there is variation attributable to reproductive stage in lymphocyte subsets and major histocompatibility complex (MHC) class II expressing cells in mammary glands of sows. ANIMALS: 8 healthy primiparous crossbred sows that had been nursing piglets for 30 to 35 days. PROCEDURE: Needle biopsy of the mammary gland was performed after parturition, at midlactation, and after weaning. Various lymphocyte subsets and MHC class II expressing cells were detected immunohistochemically, using monoclonal antibodies. RESULTS: The number of CD8+ cells was significantly lower after parturition than after weaning but not significantly lower than at midlactation. The number of IgA-bearing cells was lower after parturition and after weaning than at midlactation. There were more B cells at midlactation than after weaning. There was no change over time in the number of CD4+ cells or MHC class II expressing cells. Immunohistochemically positive cells were detected only in interalveolar tissue. CONCLUSIONS AND CLINICAL RELEVANCE: Certain lymphocyte subsets in mammary glands of sows are affected by reproductive stage. The data do not support the hypothesis that development of postparturient coliform mastitis may be the result of impaired mammary immune defenses at parturition.