Potent Cytolytic Response by a CD8+ CTL Clone to Multiple Peptides from the Same Protein in Association with an Allogeneic Class I MHC Molecule

Abstract

CTL clone 2C recognizes the allogeneic class I MHC molecule Ld in association with peptides derived from α-ketoglutarate dehydrogenase (oxoglutarate dehydrogenase (OGDH)), a ubiquitous intracellular protein. One of these peptides, QLSPFPFDL (QL9), elicits more vigorous cytolytic responses than two previously identified naturally processed peptides with overlapping sequences, LSPFPFDL (p2Ca) and VAITRIEQLSPFPFDL (p2Cb), from OGDH. In this study, we show that QL9 forms a more stable complex with cell surface Ld than does p2Ca or p2Cb and is processed from the longer, naturally occurring peptide p2Cb by 20S proteosomes in vitro. The N-terminal cyclized pyroglutaminyl QL9 (pyroQL9), a form of QL9 to which it is converted at the low pH used for peptide isolation from tissue extracts, is even more active than QL9 in cytotoxicity assays with 2C CTL. Overall, the results indicate that along with the abundant natural peptides p2Ca and p2Cb, the QL9 and other OGDH peptides of various lengths, sharing a conserved C-terminal sequence, are also processed and presented with Ld as allogeneic ligands for T cells expressing 2C TCR. All these peptides, each available in a low amount, could act in concert at the cell surface, resulting in a high density of cognate ligands that accounts for the exceptionally potent cytolytic response by 2C CTL.

Direct Recognition of Foreign MHC Determinants by Naive T Cells Mobilizes Specific Vβ Families Without Skewing of the Complementarity-Determining Region 3 Length Distribution

“…Because prominent recognition of the peptide by the CDR3 region of the TCR would have resulted in altered usage of CDR3 lengths, these results are consistent with the model derived from structural analyses of the molecular interactions involved in direct allorecognition. Indeed, the large number of contacts made by the TCR with the MHC framework (11,12) and the relatively low sensitivity to peptide sequence variations (17,18,43) suggest that direct recognition of nonself-MHC molecules by T cells may be more dependent on interactions of the TCR with the allo-MHC framework determinants than with the peptide itself (20). This low peptide specificity has also been recently suggested by the low contact number between the CDR3 regions of the BM3.3 TCR and an allogeneic MHC-peptide ligand (44).…”

The contributions of mass spectrometry to understanding of immune recognition by T lymphocytes

“…The answer is not altogether clear. The number of peptide-MHC complexes required for T lymphocyte recognition varies from several thousand per target cell to as few as one [25,[28][29][30][31][32][33], although weak recognition of other peptides may contribute to the T cell activation process [34]. Some studies have shown a direct correlation between cell surface densities of individual peptide antigens and the magnitude of the immune response against them [35][36][37][38][39], but other studies have shown exactly the opposite [25,27,40].…”

A Peptide That Antagonizes TCR-Mediated Reactions with Both Syngeneic and Allogeneic Agonists: Functional and Structural Aspects

“…When, however, the target cells expressed L d , background lysis values were higher (ϳ20%) because some naturally occurring (endogenous) cellular peptides associate with L d to form pMHC agonists for 2C cells (10,12). Background lysis values were not subtracted from the reported results.…”