The impact of HLA-G levels and endometrial NK cells in the uterine flushing from primary and secondary unexplained female infertility

P-254 The impact of HLA-G levels and endometrial NK cells in the uterine flushing from primary and secondary unexplained female infertility Study question: To determine the value of human leukocyte antigen (HLA)-G levels and endometrial Natural Killer (NK) cell percentages in uterine flushing from primary and secondary infertile women. Summary answer: This study, for the first time in literature, indicates that lower soluble (s)HLA-G levels and the decrease in endometrial CD56+ KIR2DL4+ NK cells in the uterine flushing are associated with primary unexplained infertility. What is known already: NK cells are the dominant type of maternal immune cells in the endometrium and they play a major role in determining pregnancy outcomes. HLA-G molecules are non classical HLA class I antigens character- ized by a tolerogenic function during pregnancy. In particular, they are expressed by cythotrophoblast and they bind the KIR2DL4 receptor expressed by the uter- ine NK cells. This interaction controls the activation of the uterine NK cells and promotes the formation of the placenta. Study design, size, duration: Twenty women affected by primary (N = 14) or secondary (N = 6) unexplained infertility were recruited. The mean dura- tion of infertility was 2.8 ± 1.7 years and the mean age of the patients was 35.4 ± 3.6 years. Uterine flushing was obtained during Hysterosalpingo-contrast sonography 7–9 days after menstruation. Participants/materials, setting, methods: sHLA-G levels were tested in uterine flushing samples using HLA-G specific enzyme immunosorbent assay with a specific antibody (MEM-G9). The cells obtained from the uterine flush- ing pelletization were analyzed by flow cytometry with CD3, CD56, CD158d monoclonal antibodies. The data were compared by Mann Whitney U test and logistic regression. Main results and the role of chance: sHLA-G levels were undetectable in the uterine flushing samples of primary infertile women, as opposed to women affect- ed by secondary infertility (p < 0.001). Furthermore, lower CD56+KIR2DL4+ NK cell percentages were detected in the uterine flushing samples of primary infertile women compared to secondary infertile women (p = 0.0005). Hormonal and demographic parameters (FSH, LH, E2, progesterone, prolactin, TSH and FT4 levels, smoke habits, age and weight) proved not to be related with primary and secondary infertility. Limitations, reason for caution: This study is based on a limited sample size. These data should be confirmed in a larger cohort of subjects. Wider implications of the findings: These observations are in agreement with the important role of HLA-G molecules and NK cells during pregnancy. This is the first study demonstrating that primary and secondary unexplained infertility cases are characterized by different basal sHLA-G levels and CD56+KIR2DL4+ NK cell percentages. Thus, these factors concur to the achievement of an adequate uterine micro-environment for embryo implantation. Study funding/competing interest(s): Funding by national/international organization(s).Thisstudywassupportedby“AlessandroLiberatiYoungScientists Award 2013 - Regione Emilia Romagna” PRUA1GR-2013-00000084. Trial registration number: None.