The majority of immunogenic epitopes generate CD4+ T cells that are dependent on MHC class II-bound peptide-flanking residues.
Peptides bind to MHC class II molecules with a defined periodicity such that the peptide-flanking residues (PFRs) P-1 and P11, which lie outside the core binding sequence (P1-P9), are solvent exposed and accessible to the TCR. Using a novel MHC class II:peptide binding assay, we defined the binding register for nine immunogenic epitopes to formally identify the flanking residues. Seven of the nine epitopes, restricted by H-2A(k), H-2A(g7), or H-2E(k), were found to generate T cells that were completely dependent on either P-1 or P11, with dependency on P-1 favored over P11. Such PFR dependency appears to be influenced by the type of amino acid exposed, in that residues that can form salt bridges or hydrogen bonds are favored over small or hydrophobic residues. Peptides containing alanine substitutions at P-1 or P11 in place of PFRs that mediate dependency were considerably less immunogenic and mediated a substantially reduced in vitro recall response to the native protein, inferring that PFR recognition increases immunogenicity. Our data suggest that PFR recognition is a common event characteristic of all MHC class II-restricted T cell responses. This key feature, which is not shared by MHC class I-restricted responses, may underlie the broad functional diversity displayed by MHC class II-restricted T cells.
Arnold
Paula Y
PY
Department of Immunology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
La Gruta
Nicole L
NL
Miller
Tim
T
Vignali
Kate M
KM
Adams
P Scott
PS
Woodland
David L
DL
Vignali
Dario A A
DA
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000276:immunology; D000818:Animals; D001667:Binding, Competitive / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism*; D018984:Epitopes, T-Lymphocyte / Q000276:immunology* / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000276:immunology / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000276:immunology / Q000378:metabolism*; D006825:Hybridomas; D007527:Isoenzymes / Q000276:immunology / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009113:Muramidase / Q000276:immunology / Q000378:metabolism; D009842:Oligopeptides / Q000138:chemical synthesis / Q000276:immunology* / Q000378:metabolism*; D011485:Protein Binding / Q000276:immunology
D018984:Epitopes, T-Lymphocyte; D000949:Histocompatibility Antigens Class II; D007527:Isoenzymes; D009842:Oligopeptides; C421864:hen egg lysozyme; D009113:Muramidase; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2