Perforin expression in human cell–mediated luteolysis

After ovulation and in the absence of fertilization, the human corpus luteum regresses in an orderly sequence of morphological changes. This study demonstrated that luteal regression involved progressive infiltration of lymphocytes and macrophages. The inflammatory infiltrate began in the theca externa and gradually invaded granulosa cells, with maximum accumulation of lymphocytes and macrophages at the time of menstruation. Immunoperoxidase staining showed that the majority of lymphocytes were CD2⁺, CD3⁺, CD8⁺ T lymphocytes, and 15% of these T cells expressed perforin, a cytolytic protein implicated as a mediator of cytotoxicity. The remaining mononuclear infiltrate showed strong reactivity with monocyte/macrophage markers. These findings indicate that (a) a physiologic cell-mediated inflammatory process in the regressing human corpus luteum is mediated mainly by CD8⁺ T lymphocytes and cells of monocyte/macrophage lineage and (b) perforin expression in T lymphocytes supports a possible role for cytolytic T cells during the physiologic inflammatory response in human luteolysis.