Influence of the Estrous Cycle on the Presence and Distribution of Immune Cells in the Rat Reproductive Tract

PROBLEM: Previous studies have shown that the uterus and vagina contain cells that can present antigen to ovalbumin-specific T-cells. The objective of the present study was to systematically characterize the immune cells [major histocompatibility complex (MHC) class-II+, macrophages, granulocytes, dendritic cells, and CD8+ cells] present in the uterus and vagina of the rat and to examine their distribution at various stages of the estrous cycle. METHOD OF STUDY: Uterine and vaginal tissues from female rats were selected at various stages of the estrous cycle and were examined by immunohistochemical analysis. MHC class-II (Ia)-positive cells were detected using the OX-6 monoclonal antibody; macrophages, granulocytes, and dendritic cells were detected by OX-41 monoclonal antibody and CD8-positive T-cells were identified by OX-8 monoclonal antibody. RESULTS: Immunohistochemical analysis showed cycle-dependent changes in the immune cell populations in the uterus and vagina. Ia+ cells, macrophages, granulocytes, and dendritic cells were present in large numbers in the stroma of the endometrium and around the glandular epithelium in the uterus at estrus, the stage of the reproductive cycle when estradiol levels are known to be high, relative to those seen at diestrus, when estrogen levels are low and progesterone is the predominant hormone. CD8+ cells were observed in the uterus interspersed between glandular epithelial cells at estrus. Immune cells were more numerous in the vagina, relative to the uterus. OX-6 and OX-41-positive cells were present in greater numbers in the subepithelial layers of the vagina at diestrus, in contrast to estrus. CONCLUSION: This study demonstrates that a variety of immune cells are present in the reproductive tract and that their number and distribution vary in a tissue-specific manner with the stage of the estrous cycle.