Endometriosis is a widespread chronic disease characterized by endometrial tissue located outside the uterine cavity. Clinical signs are chronic pelvic pain and infertility. Emerging evidence indicates that the immune system is profoundly involved in the onset and/or progression of endometriosis. However, mechanistic pathways have not yet been conclusively specified. In this study, women undergoing diagnostic laparoscopy due to infertility were recruited, and classified as early-stage endometriosis (n=30), advanced-stage endometriosis (n=8) or no endometriosis (n=31). The frequency and phenotype of leukocytes were evaluated in peritoneal fluid. While the frequency of lymphocytes was not significantly different, neutrophils were increased in endometriosis. Flow cytometry analysis revealed an increased frequency of CD4(+) and CD8(+) cells in peritoneal fluid of endometriosis patients. In addition, the frequency of CD4(+)CD25(+)CD103(+) cells and lineage(-)HLA-DR(+)CD11c(+)CD123(+) dendritic cells was decreased in peritoneal fluid in endometriosis, whereas CD57(+) NK cells and CD8(+)CD28(-) T suppressor cells remained largely unaltered. We conclude that therapeutic approaches in endometriosis might focus on peritoneal leukocytes as a target or surveillance marker; however, immune alterations in peritoneal fluid are subtle and their analysis will require highly standardized and harmonized protocols.
