Potential impact of maternal vitamin D status on peripheral blood and endometrium cellular immunity in women with recurrent implantation failure

Abstract Problem This study aims to evaluate the modulatory effects of vitamin D on peripheral blood and endometrial cellular immunity in women with recurrent implantation failure (RIF). Method of study One hundred and fifty‐four women with RIF were identified at a fertility center from January 2018 and March 2019. Blood and endometrium samples were collected during the mid‐luteal phase before IVF treatment or pregnancy. The serum vitamin D status, NK cell cytotoxicity, Th1 cytokine production, and endometrial immune cells were detected before and after vitamin D supplementation. Results The NK cell cytotoxicity at an effector:target (E:T) ratio of 50:1 or 25:1 was significantly higher in vitamin D insufficiency group (VDI) than those in vitamin D normal group (VDN) ( P < .05 each). The percentage of IFN‐γ‐ or TNF‐α‐producing Th cells was significantly increased in VDI or vitamin D deficiency group (VDD) when compared with VDN ( P < .05 each). The percentage of CD68 + macrophages on all endometrial cells in VDI and VDD was significantly higher than in VDN ( P < .05 each), while no significant differences in the percentage of other endometrial immune cells among the three groups were observed. This dysregulation was significantly reduced with vitamin D supplementation. Conclusion Our findings highlighted that vitamin D may have an important role in the regulation of not only systemic but also local immune response for optimization of maternal tolerance for implantation in women with RIF. Pre‐conception optimization of vitamin D status should be considered in women with RIF.