Introduction
Featuring the presence of endometrial tissue outside the uterine cavity, endometriosis is a chronic inflammatory disorder resulting in pelvic pain and infertility [1]. Various immune cell types including neutrophils, macrophages, natural killer (NK) cells, dendritic cells, and T lymphocytes play significant roles in the initiation and progression of endometriosis [2]. Immune cells secret biochemical factors that facilitate endometriotic cell division, invasion, as well as angiogenesis [3]. However, the exact functions and regulatory mechanisms of these immune cells have not been thoroughly understood.
Previous findings suggest that imbalanced T cell subsets and/or T cell dysfunction significantly contribute to the elevation of pathological cytokines and inflammatory reactions at endometriosis tissues. Cytokines released by peritoneal T cells are predominantly T helper 2 (Th2) cytokines in endometriosis tissue [4]. Regulatory T cell deficiency seems to promote local inflammation, angiogenesis, and facilitate the attachment and growth of endometrial implants [5]. Recent studies have revealed the role of T helper 17 (Th17) cells in endometriosis pathophysiology. Th17 cells are defined by the secretion of IL-17A, a pro-inflammatory cytokine crucial for the development of inflammatory and autoimmune diseases. The proportion of Th17 cells in endometriosis lesions is higher than that in the normal endometrium [6], and their high proportion in peritoneal fluid (PF) is related to the severity of endometriosis [7]. Additionally, the functional features and underlying regulatory mechanisms of Th17 cells in endometriosis are yet to be completely understood. It is, therefore, important to isolate live Th17 cells from blood, lymphoid organs, PF, and endometriosis lesions to disclose the molecular characteristics critical to their activities. Unfortunately, previous and current Th17 studies in endometriosis patients rely on intracellular staining of IL-17A for flow cytometry analysis, making the isolation of live Th17 cells impractical. A novel approach to sort live Th17 cells is in urgent demand for endometriosis research. Several research groups have used an array of chemokine receptors to dissect T cell subsets including Th17 cells in other diseases [8-11]. However, whether these receptors apply to Th17 detection in endometriosis remains untested.
In the present study, we use a set of cell surface markers to detect and sort live Th17 cells from PF of patients with advanced/severe endometriosis. We found that CCR4, CCR6, IL-17RE, and CD27 defined live PF Th17 cells. Moreover, RNA-Seq analysis revealed significant distinct transcript profiles of PF Th17 subpopulations. Therefore, our data disclose the heterogeneity of PF Th17 cells in endometriosis.