Different forms of endometriosis have specific immunological features: ovarian endometriosis combines local immunosuppression with systemic inflammation, adenomyosis is characterized by pro-inflammatory changes with a Treg cell deficiency, and deep infiltrating endometriosis is distinguished by the activation of the IDO1/COX-2/MMP-9 signaling pathway and complement-mediated tissue destruction. Here, IDO1 is linked to endometriosis.