The HLA-A2 Restricted T Cell Epitope HCV Core35–44 Stabilizes HLA-E Expression and Inhibits Cytolysis Mediated by Natural Killer Cells

Abstract

Impaired activity of natural killer cells has been proposed as a mechanism contributing to viral persistence in hepatitis C virus (HCV) infection. Natural cytotoxicity is regulated by interactions of HLA-E with inhibitory CD94/NKG2A receptors on natural killer (NK) cells. Here, we studied whether HCV core encodes peptides that bind to HLA-E and inhibit natural cytotoxicity. We analyzed 30 HCV core-derived peptides. Peptide-induced stabilization of HLA-E expression was measured flow cytometrically after incubating HLA-E-transfected cells with peptides. NK cell function was studied with a (51)chromium-release-assay. Intrahepatic HLA-E expression was analyzed by an indirect immunoperoxidase technique and flow cytometry of isolated cells using a HLA-E-specific antibody. We identified peptide aa35-44, a well-characterized HLA-A2 restricted T cell epitope, as a peptide stabilizing HLA-E expression and thereby inhibiting NK cell-mediated lysis. Blocking experiments confirmed that this inhibitory effect of peptide aa35-44 on natural cytotoxicity was mediated via interactions between CD94/NKG2A receptors and enhanced HLA-E expression. In line with these in vitro data we found enhanced intrahepatic HLA-E expression on antigen-presenting cells in HCV-infected patients. Our data indicate the existence of T cell epitopes that can be recognized by HLA-A2 and HLA-E. This dual recognition may contribute to viral persistence in hepatitis C.

Synergistic inhibition of natural killer cells by the nonsignaling molecule CD94

“…In vivo HLA-E presents a mixture of peptides derived from the leader sequences of HLA class I molecules, and during infection viral peptides also may be presented (26). To rationalize our findings with previous work, we performed further degranulation assays using combinations of HCV core [35][36][37][38][39][40][41][42][43][44] and MHC class I leader peptides (27). In the presence of HCV core [35][36][37][38][39][40][41][42][43][44] , inhibition of killing mediated by 1 μM HLA-G sp was enhanced twofold ( Fig.…”

“…These residues interact primarily with the nonsignaling CD94 moiety, which occupies the majority of the HLA-E-binding interface. CD94-NKG2A seems to be a target for viral escape, with peptides derived from CMV, HCV, HIV, and EBV binding HLA-E and subsequently inhibiting NK cells (24)(25)(26)(27). Viral peptides that inhibit at KIR also are identifiable (28), but their relevance likely is limited to the subset of individuals who have the relevant peptide-binding MHC class I allele.…”

“…[35][36][37][38][39][40][41][42][43][44] Stabilizes HLA-E but Requires HLA Class I Leader Peptides to Inhibit NKG2A + NK Cells. HCV core [35][36][37][38][39][40][41][42][43][44] (YLLPRRGPRL) is a known HLA-A2 CTL epitope that also up-regulates HLA-E expression (27). Therefore we investigated whether HCV core [35][36][37][38][39][40][41][42][43][44] could inhibit NK cells via NKG2A.…”

Identification of effector-memory CMV-specific T lymphocytes that kill CMV-infected target cells in an HLA-E-restricted fashion

“…The first identified were conserved peptides derived from the leader sequence of various HLA class I alleles [12]; binding of these peptides enables surface expression of HLA-E molecules in most normal cells [13]. Subsequently, several HLA-Ebinding peptides have been identified that were derived from viruses, including CMV [5,[14][15][16].…”

“…the AD-169 UL40 [15][16][17][18][19][20][21][22][23] VMAPRTLIL peptide) is identical to a peptide common to the leader sequence of various HLA-Cw alleles [5]. Available in high amounts during CMV infection, it binds to HLA-E molecules and enables their expression at the cell surface.…”