Objective
To investigate menstrual cycle changes in expression by eutopic endometrium of a nonclassic human leukocyte antigen, HLA-G, which binds to the killer immunoglobulin-like receptor (KIR) 2DL4 (CD158d) on natural killer (NK) cells. Such antigens have been linked to endometriosis. Design: Case-control study. Setting: University hospital. Patient(s): We examined 20 Japanese women undergoing hysterectomy for endometriosis and 17 undergoing hysterectomy for myoma. Intervention(s): Immunohistochemical HLA-G staining of eutopic endometrium and peritoneal fluid (PF) cells from women with and without endometriosis. Flow cytometric analysis of PF NK cells from women with and without endometriosis. Main outcome measure(s): HLA-G staining in eutopic endometrium was quantified by image analysis. The KIR2DL4-expressing NK cells in PF were investigated by flow cytometry. Result(s): The HLA-G was expressed by eutopic endometrium only in the menstrual phase and not in the late proliferative or secretory endometrium. Intensity of HLA-G staining did not differ significantly between women with and without endometriosis. The HLA-G- expressing cells were detected in PF during the menstrual period. These cells are morphologically and flow cytometrically different from mesothelial cells and NK cells.