An immunohistological study of MHC class II expression and T lymphocytes in the endometrium of the mare.

The distribution of T lymphocytes and of cells bearing MHC Class II antigens in the endometrium of the mare was studied using an avidin-biotin-peroxidase staining method. The cells within the endometrium which expressed MHC Class II were macrophages, lymphocytes, monocytes, dendritic cells, epithelial cells and endothelial cells. MHC Class II expression increased significantly (P < 0.05) in the luminal epithelium and tended (P = 0.0573) to increase in the subepithelial layers during oestrus. Numbers of T lymphocytes did not differ between oestrus and dioestrus. MHC Class II expression and T lymphocyte numbers were not significantly different in samples collected on Day 14 of dioestrus and on Day 14 of pregnancy. The presence of endometritis greatly increased MHC Class II expression and T lymphocyte numbers within the endometrium.