LACTATION STAGE-DEPENDENT CHANGES OF LYMPHOCYTE SUBPOPULATIONS IN MAMMARY SECRETIONS - INVERSION OF CD4(+) CD8(+) T-CELL RATIOS AT PARTURITION/

PROBLEM: Determination of lactation stage-dependent changes in levels of lymphocyte subpopulations in milk. METHOD: Flow cytometric assay wa s used to identify and assay lymphocyte subpopulations in bovine milk at different stages of lactation. RESULTS. Lymphocyte subpopulations i n mammary secretions of dairy cows change during the lactation cycle. In involuting glands (dry gland), similar to 80-90% of lymphocytes wer e CD2(+) T cells. The proportion of CD2(+) T cells, however, decreased to similar to 50% at the colostral stage and fluctuated between 50 to 60% in normal (mature) milk. Throughout the lactation stages, less th an 5% were B cells as identified by the monoclonal antibodies against CD21 and MHC class II antigens. Subset analysis showed, however, that the proportion of CD5(+) T cells decreased from 90% in involuting glan d secretions to 75% in colostrum (peripartum stage). and to similar to 40-50% in the normal (mature) milk. CD4(+) T cells constituted betwee n 45 to 55% of lymphocytes in the dry gland secretion but decreased dr astically at parturition and maintained at the level below 20% through out normal lactation. In contrast, the proportion of CD8(+) T cells in the dry gland secretion was low, between 30 to 40%. but increased ste adily, in an inversely-related manner with that of CD4(+) T cells, to similar to 40-50% at parturition and maintained at similar to 30-40% d uring the normal lactation stage thereafter. Two-color immunofluoresce nce study revealed further that practically all of the CD8(+) cells in dry gland secretions were CD2(+), and approximately 40% of them were CD5(-). Throughout th; lactation cycle, WC1(+)gamma delta T cells comp rised only 2 to 5% of lymphocytes in mammary secretions. CONCLUSIONS: T lymphocyte subpopulations change dynamically during stages of the la ctation cycle. The selective migration of T lymphocyte subpopulations to and from the mammary gland, and their functional roles in the immun e competence and regulation of the dam and sucklings remain to be eluc idated.