Increased levels of C1q, C1 inhibitor, mannose-binding lectin (MBL), C3c, C4, and the membrane attack complex (SC5b-9) in the peritoneal fluid of endometriosis patients. Increased expression of 1QA, C1QB, C1R, C1S, C2, C3, C4A/B, C5, C6, C7, C8A, CFB, CFH, and CFI in ectopic endometrium. This evidence concerns the gene C2 and endometriosis.