Demonstration and characterization of HLA-DR positive cells in the stroma of human endometrium

The proportion of stromal cells expressing DR antigens of the HLA system or reacting with an anti-macrophage antibody was studied by immunohistochemical methods in human proliferative, secretory and post-menopausal endometria. DR+ cells showed a rounded morphology with short expansions and represented 13-25% of the stromal cells in the proliferative and 16-43% in the secretory endometrium. The cells reacting with the anti-macrophage antibody were similar to DR+ cells, but their number was between 1/2 and 1/10 of DR+ cells. In the post-menopausal endometria no DR+ cells or elements reacting with anti-macrophage antibody were observed. These results suggest that a significant proportion of endometrial stromal cells expressing type II histocompatibility antigens do not belong to the monocyte-phagocyte system and that their number is under hormonal regulation.