Biopsy-free Profiling of the Uterine Immune System in Patients with Recurrent Pregnancy Loss and Unexplained Infertility

Research question: What are the differences in menstrual blood lymphocytes between controls, patients with recurrent pregnancy loss (RPL) and patients with unexplained infertility (uINF)?Design: Prospective study including 46 healthy controls, 28 RPL and 11 uINF patients. A feasibility study compared lymphocyte compositions of endometrial biopsies and menstrual blood collected during the first 48 h of menstruation in seven controls. In all patients, peripheral and menstrual blood from the first and subsequent 24 h were analysed separately by flow cytometry, focusing on the main lymphocyte populations and natural killer (NK) cell subsets.Results: The first 24 h of menstrual blood resembles the uterine immune milieu as tested by endometrial biopsy. RPL patients showed significantly higher menstrual blood CD56+ NK cell numbers than controls (mean & PLUSMN; SD: 31.13 & PLUSMN; 7.52% versus 36.73 & PLUSMN; 5.4%, P = 0.002). Menstrual blood CD56dimCD16bright NK cells within the CD56+ NK cell population were decreased in RPL (16.34 & PLUSMN; 14.65%, P = 0.011) and uINF (15.7 & PLUSMN; 5.91%, P = 0.02) patients versus control (20.42 & PLUSMN; 11.53%). uINF patients had the lowest menstrual blood CD3+ T cell counts (38.81 & PLUSMN; 5.04%, control versus uINF: P = 0.01) and cytotoxicity receptors NKp46 and NKG2D on CD56brightCD16dim cells were higher in uINF (68.12 & PLUSMN; 11.84%, P = 0.006; 45.99 & PLUSMN; 13.83%, P = 0.01,respectively) and RPL (NKp46: 66.21 & PLUSMN; 15.36%, P = 0.009) patients versus controls. RPL and uINF patients had higher peripheral CD56+ NK cell counts versus controls (11.42 & PLUSMN; 4.05%, P = 0.021; 12.86 & PLUSMN; 4.29%, P = 0.009 versus 8.4 & PLUSMN; 3.5%).Conclusions: Compared with controls, RPL and uINF patients had a different menstrual blood-NK-subtype profile, indicating an altered cytotoxicity. In future studies, this non-invasive analysis might enable identification and monitoring of patients receiving immunomodulatory medications.