The endometria of patients with endometriosis show higher expression of class I human leukocyte antigen than the endometria of healthy women

To compare the expression of class I human leukocyte antigen (HLA I) in endometrial samples from patients with and without endometriosis. Cross-sectional study. Acute-care teaching hospital in Barcelona, Spain. The endometriosis group included 32 patients for whom the only diagnosis during an operation was endometriosis. The control group included 20 women who underwent a laparoscopy and in whom no evidence of endometriosis or any other genital disease was seen. Samples of endometrium were obtained by curettage and immediately frozen. A pan–HLA I mouse antihuman IgG2a monoclonal antibody was used for immunohistochemical study. Frequency of positive glandular and stromal cells was evaluated in each section. A significantly higher expression of HLA I in the endometriosis group than in controls, both in the glandular cells (median 100% vs. 80%) and in the stromal cells (median 60% vs. 20%), was observed. Patients with endometriosis had a significantly higher expression of HLA I molecules in endometrial cells than did the controls. This could be a possible explanation for their higher resistance to natural killer cytolysis.