The study of high-affinity TCRs reveals duality in T cell recognition of antigen: specificity and degeneracy.
TCRs exhibit a high degree of Ag specificity, even though their affinity for the peptide/MHC ligand is in the micromolar range. To explore how Ag specificity is achieved, we studied murine T cells expressing high-affinity TCRs engineered by in vitro evolution for binding to hemoglobin peptide/class II complex (Hb/I-Ek). These TCRs were shown previously to maintain Ag specificity, despite having up to 800-fold higher affinity. We compared the response of the high-affinity TCRs and the low-affinity 3.L2 TCR toward a comprehensive set of peptides containing single substitutions at each TCR contact residue. This specificity analysis revealed that the increase in affinity resulted in a dramatic increase in the number of stimulatory peptides. The apparent discrepancy between observed degeneracy in the recognition of single amino acid-substituted Hb peptides and overall Ag specificity of the high-affinity TCRs was examined by generating chimeric peptides between the stimulatory Hb and nonstimulatory moth cytochrome c peptides. These experiments showed that MHC anchor residues significantly affected TCR recognition of peptide. The high-affinity TCRs allowed us to estimate the affinity, in the millimolar range, of immunologically relevant interactions of the TCR with peptide/MHC ligands that were previously unmeasurable because of their weak nature. Thus, through the study of high-affinity TCRs, we demonstrated that a TCR is more tolerant of single TCR contact residue substitutions than other peptide changes, revealing that recognition of Ag by T cells can exhibit both specificity and degeneracy.
Donermeyer
David L
DL
Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Weber
K Scott
KS
Kranz
David M
DM
Allen
Paul M
PM
D019943:Amino Acid Substitution / Q000276:immunology; D000818:Animals; D017951:Antigen Presentation; D002448:Cell Adhesion / Q000276:immunology; D045744:Cell Line, Tumor; D018920:Coculture Techniques; D004734:Energy Metabolism / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000276:immunology* / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D006825:Hybridomas; D008024:Ligands; D008285:Major Histocompatibility Complex / Q000276:immunology; D051379:Mice; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism*
D018984:Epitopes, T-Lymphocyte; D006454:Hemoglobins; D008024:Ligands; D010446:Peptide Fragments; D011948:Receptors, Antigen, T-Cell