Variable expression of Ia antigens in human endometrium and in chronic endometritis

Recent studies suggest that Ia antigens may be expressed in epithelial cells and that their expression may be under hormonal control. Therefore, the distribution of these antigens was studied in frozen sections of 37 human endometria with two monoclonal antibodies (Mab) to monomorphic determinants of Ia antigens using an avidin-biotin-complex (ABC) method. Five early proliferative, 9 midproliferative, 3 late proliferative, and 12 secretory endometria were examined. Two gestational endometria and six endometria with chronic endometritis were also used. Four consecutive sections from each case were stained for Ia, OKT8, Leu-3a, and B1 antigens. Throughout the cycle, the endothelial cells, many lymphocytes, and various monocytic-macrophagic cells in endometrial stroma were Ia positive. Furthermore, Ia antigens were localized to the normal endometrial epithelium. The intensity and the pattern of Ia expression, however, varied in different phases of the cycle. Ia antigens were stained weakly in endometrial glands and surface epithelium in early proliferative phase, and strongly in surface epithelium and glandular cells of the basalis and to a lesser extent of the functionalis in midproliferative and late proliferative phases. The expression of Ia antigens in epithelium was absent or focal during the secretory phase and in gestational endometria. Throughout the cycle and in gestational endometria, glandular cells in intimate association with lymphocytic aggregates were Ia positive. In chronic endometritis, the increased number of Ia positive stromal lymphoid cells was associated with a strong display of Ia antigens in epithelium. The findings indicate that, in addition to endothelial and lymphoid cells, Ia antigens are expressed in endometrial glandular and surface epithelial cells. This expression may be influenced by lymphoid cells in endometrium and by hormones.