Lack of strict correlation of functional sensitization with the apparent affinity of MHC/peptide complexes for the TCR.
We describe a comprehensive analysis of the effect of avidity of TCR-MHC/peptide interaction on activation of the (p2Ca). In study, monosubstituted variants of p2Ca were used and assessed for binding to purified H-2Ld, binding of H-2Ld/peptide complexes to sTCR, and ability to activate 2C cells to two independent effector functions. Among the > 20 variants analyzed, functional activity of most peptides that bound the MHC well correlated with the strength of interaction of MHC/peptide complexes with sTCR. However, with some variants, a clear discordance between the apparent TCR-MHC/peptide affinity and biologic function was observed, demonstrating that the former cannot always be gauged by the latter. In the case of L4 peptide (phenylalanine at position 4 substituted with leucine), peptide/MHC complexes showed no detectable binding to sTCR, indicating a 10-fold or greater decrease in affinity. Nevertheless, this peptide sensitized target cells for lysis at a level equivalent to the parental peptide. A clearer understanding was revealed by studying the extent to which activation by variant peptides was dependent on CD8. Our data indicate that resistance to anti-CD8 mAb blocking correlates with strong binding affinity between sTCR and MHC/peptide complexes. These data suggest that, for the activation of CTL function, the absolute level of intrinsic affinity of TCR for MHC/peptide ligand is not a single critical determinant, but rather, that activation is governed by the compound influence of several factors, which ensures a minimum threshold of intracellular triggering is reached to elicit the response.
al-Ramadi
B K
BK
Section of Immunobiology, Yale University School of Medicine, New Haven, CT 06520, USA.
Jelonek
M T
MT
Boyd
L F
LF
Margulies
D H
DH
Bothwell
A L
AL
D000595:Amino Acid Sequence; D000818:Animals; D016827:CD8 Antigens / Q000276:immunology; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D000939:Epitopes / Q000096:biosynthesis; D014644:Genetic Variation; D006183:H-2 Antigens / Q000276:immunology / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D007377:Interleukin-3 / Q000032:analysis; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000276:immunology*; D011948:Receptors, Antigen, T-Cell / Q000276:immunology* / Q000378:metabolism*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology
D016827:CD8 Antigens; D000939:Epitopes; D006183:H-2 Antigens; D015395:Histocompatibility Antigens Class I; D007377:Interleukin-3; D010455:Peptides; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D011948:Receptors, Antigen, T-Cell