"What do we know about regulatory T cells and endometriosis? A systematic review".

Endometriosis is a benign, chronic inflammatory disease that presents alterations in immune response that can be detected in eutopic endometrium, peritoneal fluid and peripheral blood of affected women. Regulatory T (TReg) cells are a subpopulation of T lymphocytes specialized in immune regulation that seem to participate in the development of endometriosis, by suppressing the immune response and favoring the establishment of lesions. Our aim was to review the scientific literature that evaluates TReg cell phenotypes in the context of endometriosis. PRISMA statement for systematic reviews was applied, using "regulatory T cells" and "endometriosis" as keywords in the following databases: PubMed, Cochrane, EMBASE and Lilacs. The initial search and abstract review yielded 41 papers relating to the subject. At the end, 12 studies, published between 2009 and 2016, were included. Most studies that analyzed TReg cells did not characterize these cells with current Bona Fide markers. In peritoneal fluid and endometriotic lesions, there was a higher concentration of TReg cell phenotype and/or TReg cell expression markers in patients with endometriosis when compared with controls. However, there is still not a consensus about TReg cells concentration in eutopic endometrium and peripheral blood between the revised studies. Taken together, this data collection suggests that endometriosis is related to TReg cells alterations, although further studies are necessary to reach more precise conclusions, especially regarding the percentage of these cells in eutopic endometrium and peripheral blood. This systematic review attempted to provide instructive and up-to-date collection of data that may help better design future studies.