Hcmv-miR-UL112 attenuates NK cell activity by inhibition type I interferon secretion

Viral microRNAs (miRNAs) can regulate the host innate immune response. In particular, the human cytomegalovirus (HCMV) miRNA hcmv-miR-UL112 evades the host immune system by downregulating host immune gene and immediate-early viral gene expression. Natural killer (NK) cells are important innate immune cells with potent cytotoxicity, and are activated by type I interferons (IFNs) upon infection. It remains unclear how HCMV persists in the host despite the strongly antagonistic host immune system. A lentiviral vector was used to stably express hcmv-miR-UL112 in peripheral blood mononuclear cells (PBMCs). Hcmv-miR-UL112 expression levels were detected by TaqMan miRNA assay. The effects of hcmv-miR-UL112 on NK cell cytotoxicity were assessed with CD107a mobilization assay and CytoTox 96 non-radioactive cytotoxicity assay. Enzyme-linked immunosorbent assays (ELISA) were performed to detect type I IFNs levels in culture supernatants. To confirm the role of type I IFN in hcmv-miR-UL112-mediated NK cell cytotoxicity, PBMCs were incubated with antagonizing antibodies against IFN receptor (IFNAR) before lenti-hcmv-miR-UL112 treatment and recombinant type I IFN was added back into miR-transduced PBMC. Ectopically expressed hcmv-miR-UL112 functionally attenuated NK cell-mediated cytotoxicity, associated with decreased type I IFN expression. Hcmv-miR-UL112-transfected cells did not reduce the CD107-expression further than the IFNAR neutralizing mAbs-treatment alone, and adding back of recombinant type I IFN restored CD107a expression from the miR-transduced PBMC. Taken together, our results suggest that hcmv-miR-UL112 subverts innate immunity by downregulating type I IFN signaling to inhibit NK cell cytotoxicity. These results provide a new miRNA-based immunoevasion mechanism that may be exploited by HCMV.