Endometrium infection by human herpesvirus-6A: implication in female idiopathic infertility

Abstract

We first reported HHV-6A DNA presence in 43% of endometrial cells from women with idiopathic infertility, whereas no fertile control women harbored the virus1. Growing evidence confirms this implication1-6. We investigated the effect of HHV-6A infection on the immunological status of the endometrium. This is a case-control study. The sample size guarantees to achieve a 0.8 power with 5% alpha error in detecting differences between groups. Endometrial biopsies, uterine flushing and whole blood samples were collected during the implantation (mid secretory phase) windows in 67 idiopathic infertile women. The presence of HHV-6A infection was evaluated by DNA and mRNA analysis (U22, U42, U94 genes) on endometrial cellular subsets1. We analyzed the endometrial immunological status evaluating: i) the levels of immune-regulatory HLA-G and HLA-E molecules, innate inflammatory (IL-6, IL-8, TNF-alpha), Th1 pro-inflammatory (IFN-gamma, IL-1alpha, IL-1beta, IL-12) and Th2 anti-inflammatory (IL-4, IL-10) cytokines by multiplex ELISA in uterine flushing samples; ii) endometrial receptivity to cytotrophoblasts in an endometrial 3D in vitro model; iii) natural killer (NK) cells and regulatory T cells percentage and immune-phenotype in endometrial biopsies and peripheral blood by flow cytometry. We confirmed the presence of HHV-6A infection in a 40% of idiopathic infertile women. We observed increased levels of IFN-gamma, IL-1beta and IL-12 (p<0.001; Student t test), decreased levels of both IL-4 and IL-10 (p<0.001) in uterine flushing samples from HHV-6A positive women. HLA-G and HLA-E molecules were not expressed on the surface of endometrial epithelial cells from HHV-6A positive women. As a proof of principle, endometrial biopsis positive for HHV-6A infection presented a lower permittivity to cytotrophoblasts invasion. We observed a lower amount of endometrial (e)NK cells in the endometrium of women positive for HHV-6A infection compared with endometrium negative for HHV-6A (p<0.0001; Student T test). In particular, when we analyzed (e)NK subpopulations, we observed a lower percentage of CD56brightCD16- (e)NK cells in women positive for HHV-6A infection (p<0.0001). When we looked at peripheral blood cell subsets, we observed a decrease in CD4+CD25+CD127dim/- regulatory T cells in women positive for HHV-6A infection (p=0.016). The identification of an effect of HHV-6A infection on endometrial immune status opens new perspectives in idiopathic infertile women care management. In addition, it would be possible to select antiviral therapies as novel therapeutic approaches to those idiopathic infertile women characterized by the presence of endometrial HHV-6A infection, to increase their pregnancy rate.