Studies of the immunobiology of the human major histocompatibility complex class Ib molecule, HLA-E

HLA-E is a human major histocompatibility (MHC) class Ib molecule that binds peptides derived from the leader sequence of self MHC class Ia molecules and inhibits natural killer (NK) cell-mediated lysis by engagement of the CD94/NKG2A inhibitory receptor found on NK and T cells. It is now appreciated that HLA-E and the murine class Ib molecule, Qa-1b, are functional homologues, binding a similar set of leader-derived hydrophobic peptides to inhibit cytotoxic responses via engagement of CD94/NKG2A. Recent work in our laboratory has shown that Qa-1b also binds peptides derived from bacterial and self-heat shock protein 60 molecules for presentation to a cytotoxic CD8+ T cell following Salmonella typhimurium infection.; In Chapter 1, experiments were conducted as an extension of the findings from the murine Qa-1b system. Salmonella-specific CD8+ T cells were identified in human volunteers following oral Salmonella typhi vaccination that exhibited non-MHC restricted killing, an indicator of HLA-E involvement.; The experiments comprising Chapter 2 show that heat shock protein 60-derived peptides do not bind HLA-E sufficiently well enough to inhibit NK cell-mediated lysis, but curiously, equal recognition of the CD94/NKG2A receptor is measured using HLA-E tetramers bound with leader and heat shock protein-derived peptides.; In Chapter 3, using a cell line that expresses low levels of HLA-E due to the lack of available leader peptide, we find a rapid increase in HLA-E surface expression following heat shock and subsequent inhibition of NK cell-mediated lysis using heat shocked targets. The amino acid sequence of this stress-inducible inhibitory peptide was determined using a mass spectrometry-based approach. Sequence analysis identified a novel nonamer peptide, derived from the transmembrane domain of the ABC transporter MRP7, as a major peptide eluted from the groove of HLA-E. Experiments using targets pulsed with synthetic peptides and a CD94/NKG2A+ NK cell line show that NK-mediated lysis is inhibited by the MRP7 peptide as well as leader peptide and that inhibition is reversible using both anti-CD94 and anti-class I mAbs. These findings reveal for the first time a non-leader inhibitory peptide that binds to HLA-E and further implicates HLA-E as a highly conserved and unique immuno-regulatory molecule.