HLA-E/peptide complexes differentially interact with NKG2A/CD94 and T cell receptors.

The virtually monomorphic antigen presentation molecule HLA-E can present self- and non-self peptides to the NKG2A/CD94 co-receptor inhibitory complex expressed on natural killer (NK) cells and to T cell receptors (TCRs) expressed on T cells. HLA-E presents self-peptides to NKG2A/CD94 to regulate tissue homeostasis, whereas HLA-E restricted T cells mediate regulatory and cytotoxic responses toward pathogen-infected cells. In this study, we directly compared HLA-E/peptide recognition and signaling between NKG2A/CD94 and 2 HLA-E restricted TCRs that can recognize self-peptides or identical peptide mimics from the viral UL40 protein of cytomegalovirus using position substituted peptide variants. We show that position 7 is critical for interaction with NKG2A/CD94, whereas position 8 is important for interaction with the TCRs. The Arginine at position 5 of these peptides is an essential residue for recognition by both receptors. Thus, NKG2A/CD94 and TCRs have different requirements for recognition of peptides presented in HLA-E.