Perforin expression in endometrium during the menstrual cycle

Perforin is a marker of functionally active cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. We examined perforin expression in endometrium throughout the menstrual cycle. In addition, perforin expression was studied in endometrial leukocytes in women with anovulatory cycles with or without progesterone therapy and in postmenopausal women. In the endometrium. perforin-positive endometrial lymphocytes increased in numbers in the middle through late secretory phases. In women with anovulatory cycles, the proliferative endometrium, before estrogen withdrawal endometrial break- down, contained less perforin-positive lymphocytes compared with the premenstrual endometrium of the normal menstrual cycle. The progestin-induced endometrial decidualization was accompanied by an extensive recruitment of perforin-positive cells. In contrast, the postmenopausal atrophic endometrium showed complete absence of perforin-positive cells. The lymphocytes isolated from secretory endometrium were CD3⁻, CD56⁺ (~80%) or CD3⁺, CD8⁺ T-cell receptor (TCR)-γδ⁻ (~20%). Almost 90% ± 5.5 of the CD3⁻ CD56⁺, and up to 25% ± 7% of CD8⁺ T lymphocytes contained perforin. Perforin expression w’as further confirmed in endometrial lymphocytes by Northern blot analysis. In vitro, isolated endometrial lymphocytes exhibited NK-like cytotoxicity. After cyclic hormone withdrawal during normal menstrual cycle, these perforin-positive cytotoxic cells may be involved in endometrial stromal breakdown during menstruation.