Increased expressions of CD69 and HLA-DR but not of CD25 or CD71 on endometrial T lymphocytes of nonpregnant women

To investigate lymphocyte subpopulations and the status of T-cell activation at different phases of the menstrual cycle, lymphocytes in endometrial tissue were analyzed by dual-color flow cytometry in 39 patients. Compared with peripheral blood, the lymphocytes in the endometrium had a higher CD3^- (CD56⁺or CD16⁺) ratio (25.2% ± 6.8% vs 11.1% ± 7.0%), but an inverted CD3⁺CD8^- CD3⁺CD8⁺ ratio (0.5 vs 1.8) and a minimal amount of B cells (3.3% ± 3.1%). TcR γδ⁺ T cells accounted for a minor proportion (7.8% ± 5.1%) in endometrium. The proportions of TcR αβ⁺ (85.0% ± 6.6%) and CD3⁺CD56⁺ (7.4% ± 4.4%) endometrial T lymphocytes were found significantly different from those in peripheral blood (89.1% ± 5.6% and 3.8% ± 3.4%, respectively). As the endometrium proceeded from proliferative phase to luteal phase, the proportion of CD3⁺CD8⁺ T cells in peripheral blood increased from 35.6% ± 6.9% to 41.3% ± 8.4% and CD3⁺CD8^- T cells decreased from 64.4% ± 6.9% to 58.7% ± 8.4%. The endometrial T cells expressed high levels of CD69 (84.1% ± 18.9%) and DR (75.9% ± 9.7%), but rarely expressed CD25 (7.0% ± 5.4%) and CD71 (2.8% ± 1.8%). The patterns of expression of these activation markers were similar in both proliferative and luteal phases. Our observations suggest that endometrial T lymphocytes are in a state of recent and persistent activation. Lymphocytes expressing the NK cell markers (CD56 or CD16) and CD8⁺ accounted for a significant proportion, suggesting that they may play important roles in local defense. Human Immunology 42, 227-232 (1995).