THE DISTRIBUTION OF IMMUNOGLOBULIN-CONTAINING CELLS AND T-LYMPHOCYTE SUBPOPULATIONS IN THE MOUSE MAMMARY-GLAND - A MORPHOMETRIC AND IMMUNOHISTOCHEMICAL STUDY

The distribution of immunoglobulin (Ig)-containing plasma cells and T lymphocyte subpopulations in the mouse mammary gland was studied in di fferent stages of the reproductive cycle using immunohistochemical tec hniques. Generally, Ig-containing plasma cells (IgA, IgG and IgM) in t he mammary gland were few during pregnancy. They gradually increased i n number during lactation, further increased in the first 2 days of th e post-weaning period, and then quickly decreased. The rich existence of plasma cells after the suckling period suggests that their main rol e is the protection of the mammary gland rather than the transference of passive immunity to neonates. IgA-containing plasma cells were the most frequent isotype, while IgG- and IgM-containing cells were much l ess throughout the reproductive cycle. In contrast to the plasma cells , T lymphocytes were observed to increase markedly in late pregnancy, while they gradually decreased during lactation, a further decrease be ing recognizable in the post-weaning period. CD8(+) cells, the predomi nant cell type among T cells, preferentially existed within the epithe lia of the alveoli and ducts, whereas CD4(+) cells were mainly located in the connective tissue areas. The difference in the dynamics of pla sma cells and T lymphocytes suggests that the mammary gland T lymphocy tes may lack an isotype-switching role for plasma cells.