Consistent with what has been shown previously (35), productive HIV infection was associated with a downregulation of HLA-A/B/C and an increase in the median fluorescence of the stress proteins ULBP-2/5/6 (Fig. S2A and B) that, like MHC-I chain-related proteins (MIC)-A/B, engage the activating NK cell ligand NKG2D to induce NK cell cytotoxicity (36, –, 38). Here, KLRK1 is linked to HIV infectious disease.