Direct binding of influenza peptides to class I HLA molecules

Activation of T lymphocytes requires the intracellular fragmentation of foreign antigens and their presentation by class I or class II major histocompatibility complex (MHC) glycoproteins. The direct binding of peptides to class II molecules has been demonstrated using equilibrium dialysis, gel filtration and fluorescence energy transfer at planar membranes, and its specificity compared to that of T-cell activation. In contrast, direct binding of peptides to class I molecules has been difficult to detect; although peptide sensitization experiments and the crystallographic structure of HLA-A2 (ref. 9) persuasively argue for its occurrence and importance. Here we describe a gel filtration assay from which we derive direct evidence for selective binding of an influenza matrix peptide to HLA-A2 and for binding of an influenza nucleoprotein peptide to HLA-B37. These two peptides have previously been shown to act respectively as targets for certain HLA-A2 or HLA-B37 restricted influenza-specific cytotoxic T lymphocytes (CTL). In addition we demonstrate binding to some, but not all, HLA allospecificities that cannot present these peptides to CTL. We estimate that less than 0.3% of the HLA molecules present in any given purified preparation were able to bind the added peptides.