We observed the up-regulation of FasL on the surface of eNK cells and in the uterine flushing samples of HHV-6A positive infertile women, suggesting that eNK cell killing of HHV-6A infected endometrial epithelial cells proceeds through NKG2D engagement and subsequent mechanisms dependent on the death receptor-ligand Fas/FasL pathway. This evidence concerns the gene KLRK1 and Infertility.