KLRK1 and viral infectious disease: Moreover, NKG2D has a key role in infectious diseases, given that cells respond to most viral infection by upregulating NKG2DLs and, notwithstanding various mechanisms evolved by viruses to restrain NKG2DL cell-surface expression, they become targets for NKG2D-mediated recognition and killing by NK cells, as clearly demonstrated for HIV-1-infected CD4+ T cells13.