The characteristic expression of CD3+ T cells, CD8+ T cells and CD57+ NK cells in distinct zones of peritoneal endometriotic lesions

Background: Endometriosis is a benign gynecological condition, associated with a dysfunctional immune response that facilitates progression of peritoneal lesions. Specific immune cells are hypothesized to be recruited to peritoneal endometriotic lesions; though little is known about the significance of specific T and NK cell expression and the microanatomical zoning of lesions. This study aimed to characterize the zoning of T and NK cell populations in endometriotic peritoneal lesions compared to histologically normal peritoneum. Methods and Results: Immunohistochemical analysis of CD3+ and CD8+ T cells and CD57+ NK cells in 18 peritoneal endometrial lesions and 20 normal peritoneal biopsies revealed greatly increased expression of these immune cells in women with confirmed endometriosis. Alpha-smooth muscle actin (alpha-SMA) antibody was used to detect the reactive alpha-SMA zone surrounding the core glands and stroma. CD57+ NK cells and CD3+ and CD8+ T cells were significantly over-expressed (p<0.01) throughout the peritoneal endometriotic lesions compared to normal peritoneum (in women without endometriosis) and these cells were highly expressed in the core lesion zone compared to expression in the adjacent alpha-SMA zone and surrounding peritoneum. Conclusions: Our observations support the concept that immune cell populations are recruited into developing endometriotic lesions. We have for the first time shown that NK and T immune cells are distributed differentially across various microanatomical zones of peritoneal lesions. Such understanding of zone specific immune-cell expression is crucial for better defining the roles these immune cells play in endometriotic lesion establishment and progression.