The role of immune dysfunction in the progression of endometriosis was highlighted by Maeda and colleagues [7,8,9], who found, by using flow cytometry, that the levels of NK cell inhibitory receptors such as CD158a+ and KIR2DL1+ were significantly higher in the peritoneal fluid of endometriosis subjects than controls. The gene discussed is KIR2DL1; the disease is endometriosis.