Regulation of leucocyte subpopulations in the sheep endometrium by progesterone.

To determine whether progesterone causes a change in lymphocyte subpopulations in the endometrium, frozen sections of intercaruncular and caruncular endometrium from ewes receiving daily i.m. injections of 100 mg/day progesterone were evaluated by immunohistochemistry for the presence of lymphoid cells bearing CD45, major histocompatibility complex (MHC) class II, CD45R, CD4 and CD8 antigens. The pattern of lymphocyte distribution in the uterine endometrium of untreated ewes was similar to previous reports. Progesterone treatment, particularly after 60 days, caused reductions in numbers of CD45+ cells in the glandular epithelium and associated subepithelial stroma, MHC class II+ cells in all regions of the intercaruncular endometrium and CD45R+ cells in all epithelial regions of intercaruncular and caruncular endometrium. These data demonstrate a role for progesterone in regulating migration or proliferation of endometrial lymphocyte populations; this action of progesterone may represent an important mechanism by which progesterone modifies uterine immune function.