PD-1 Expression in Endometriosis

Background: Endometriosis, believed by many to be rooted in immunology, is a chronic disease. Upregulation of programmed cell death protein 1 (PD-1) in immune cells may compromise their defensive function, a mechanism demonstrated in the context of cancer spread. This study aims to explore the potential involvement of PD-1 in the pathophysiology and progression of endometriosis. A total of 62 patients who underwent laparoscopic surgery were analyzed, with 47 diagnosed with endometriosis and 15 serving as controls. We collected peritoneal fluid and peripheral blood samples during surgery and examined them using flow cytometry. Using a panel of monoclonal antibodies, the samples were stained and the expression of PD-1 in immune cells was evaluated. Results: We observed a statistically significant rise in the percentage of the CD56+ CD16+ NK cell subset expressing PD-1 within the peritoneal fluid of endometriosis patients compared to the control group (p = 0.021). Similarly, we found that PD-1 expression on immune cells significantly differed based on factors such as body mass index and smoking habits. Moreover, peritoneal subsets of PD-1+ T and NK cells showed an increase in patients presenting symptomatic endometriosis and those with more widespread disease. Conclusions: Our evaluation of the inhibitory PD-1 receptor has strengthened the potential connection between immune escape mechanisms often seen in cancer cells and those in endometriotic cells. This concept could pave the way for future research in the field of immunomodulation and endometriosis.