Role of major histocompatibility complex class I expression and natural killer-like T cells in the genetic control of endometriosis

OBJECTIVE: To evaluate whether the expression of human leukocyte antigen (HLA) class I on eutopic and ectopic endometrial cells modify the susceptibility to lysis mediated by lymphocytes. DESIGN: Evaluation of T lymphocyte cytotoxic activity and HLA class I expression on endometrial cells. SETTING: Subjects were recruited at laparoscopy. PATIENTS: Patients with endometriosis (n = 7). Healthy women as controls (n = 10). MAIN OUTCOME MEASURES: Human leukocyte antigen class I molecule analysis of endometrial cells was carried out by immunofluorescence and flow cytometry. Phenotyping of T lymphocytes was performed to analyze T-cell subsets. Cytotoxicity was performed to determine cytolytic activity against endometrial cells. RESULTS: In vitro culture of endometrial cells down-regulates the expression of HLA class I molecules and enhances the susceptibility to lysis mediated by natural killer (NK)-like T lymphocytes. Cytolytic T-cell clones, expressing the CD94 antigen, are inhibited by the HLA-B7 allele on endometrial cells. Ectopic endometrial cells modulate the expression of HLA class I molecules. CONCLUSIONS: The resistance to lysis of endometrial cells is related to expression of surface HLA class I molecules, which send a negative signal for lysis mediated by NK-like T lymphocytes. The HLA-B7 allele inhibits the cytotoxic activity, suggesting that the growth of ectopic endometrial cells might be under a genetic control.