Human leukocyte antigen E in human cytomegalovirus infection： friend or foe

Human cytomegalovirus （HCMV） is a well-studied [3-her- pesvirus virus, which adopts a variety of strategies to evade immune surveillance. It has been reported that in HCMV-infected cells, classical major histocompatibility （MHC） class I molecules are down-regulated, but the MHC class Ib molecule human leukocyte antigen （HLA）- E is normally expressed or even overexpressed on the cell surface. HLA-E has been first described to interact with CD94/NKG2 receptors expressed mainly on the surface of natural killer （NK） cells, thus confining its role to the regulation of NK-cell function. The engagement of CD94/ NKG2A with HLA-E, with a signal peptide of the HCMV glycoprotein UL40, usually induces inhibitory signals. However, HLA-E also serves as a ligand for the TCR expressed by oLI~CD8＋ T cells. Recognition of peptides presented by HLA-E may result in CD8＋ effector T-cell activation. These findings will help to understand more on both pathogenic and protective roles of HLA-E in HCMV infection. In this review, we discussed recent studies about the roles of HLA-E in HCMV infection.