Contributions of T helper 9 cells in endometriosis-associated inflammation and lesion growth

Endometriosis is an inflammatory gynaecologic disease characterized by ectopic growth of endometrial-like tissue, resulting in pelvic pain and infertility. T-helper 9 (Th9) cells play a known role in various chronic inflammatory diseases. Despite parallels between endometriosis and Th9-driven diseases, their role in endometriosis has not been explored. We investigated Th9 cell involvement in endometriosis pathophysiology using human tissue samples, in vitro experiments with human-derived Th9 cells, and in vivo experiments to shed insight on the impact of adoptively transferred Th9 cells in our established syngeneic endometriosis mouse model. Immunohistochemistry of a tissue microarray revealed significantly increased interleukin-9 (IL-9)-positive cells in patient lesions compared to control endometrium. Human CD4+ Th cells purified from peripheral blood mononuclear cells treated with Th9-driving growth factors produced significantly increased pro-inflammatory mediators, including IL-5, IL-9 and IL-13, in response to estrogen stimulation. Adoptive transfer of murine Th9-like cells increased plasma IL-1 concentration and altered transcriptional profiles of several signalling pathways, including Notch and PI3K-Akt. Immunofluorescent microscopy depicted adoptively transferred Th9 cells present within mouse lesions. Furthermore, immunohistochemical analysis demonstrated reduced lesion proliferation following Th9-adoptive transfer. This study provides the first evidence that Th9 cells likely promote immune-inflammatory alterations within lesions to exacerbate disease.