Pro-endometriosis macrophage release of IL-33 is key for endometriosis pain and lesion formation

Endometriosis is a painful gynecological inflammatory disease affecting up to 10% of females. When released by sensory neurons, calcitonin gene-related peptide (CGRP) shapes immunity, a process known as neuroimmune communication. We previously showed that nociceptor-derived CGRP polarizes macrophages into pro-endometriosis macrophages (PEMs) that mediates endometrial epithelial (endo-epi) cell growth and pain. However, the key mediators involved in this PEM-induced cell growth were unknown. Using unbiased approaches, we discovered that nociceptor-derived CGRP induces IL-33 production by PEMs. IL-33 binding to its receptor ST2 is key for endometriotic lesion growth and pain during endometriosis in mice as anti-IL-33 antibody treatment reduced evoked and spontaneous pain as well as lesion size. Chemical or genetic ablation of nociceptors or macrophages also resulted in lower levels of lesion IL-33, demonstrating a neuroimmune-driven mechanism for IL-33 production during endometriosis. In humans, we found that IL-33 is correlated with increased number of glands and fibrosis in lesions and that IL-33 expression in macrophages is also associated with genetic risk of endometriosis. We also provided evidence that suggests a dual role for IL-33 in endometriosis, in which, it is initially required for lesion formation and later for lesion maintenance only, and associated pain. Therefore, targeting IL-33/ST2 signaling may effectively treat endometriosis pain.