Immunological aspects of external genital endometriosis: aseptic inflammation and innate immune responses

The endometrium during menstruation, as well as its fragments during intraperitoneal regurgitation, exhibit signs of aseptic inflammation. Therefore, the review summarizes current data on the possible mechanisms of survival and growth of endometrioid tissue in an atypical niche, taking into account the manifestation of signs of aseptic inflammation at the sites of heterotopia formation, and the further chronicization of inflammatory reactions in cases of widespread external genital endometriosis (EGE). The review describes the functioning of the innate immune system during EGE, as well as the interaction of HLA class I molecules, and especially HLA-G, with immunoglobulin-like receptors of killer cells during EGE, as a key link in the involvement of NK cells in the restoration of endometrial structure and the clearance of regurgitated fragments from the peritoneum during menstruation. The presented data reveal the mechanism by which concomitant inflammatory processes contribute to ectopic endometrial implantation and the formation of EGE foci.