Bk. Alramadi et al., LACK OF STRICT CORRELATION OF FUNCTIONAL SENSITIZATION WITH THE APPARENT AFFINITY OF MHC PEPTIDE COMPLEXES FOR THE TCR/, The Journal of immunology, 155(2), 1995, pp. 662-673
We describe a comprehensive analysis of the effect of avidity of TCR-M
HC/peptide interaction on activation of the alloreactive 2C CTL clone,
which recognizes H-2L(d) plus an octamer peptide (p2Ca). In this stud
y, monosubstituted variants of p2Ca were used and assessed for binding
to purified H-2L(d), binding of H-2L(d)/peptide complexes to sTCR, an
d 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 biologi
c function was observed, demonstrating that the former cannot always b
e gauged by the latter. In the case of L4 peptide (phenylalanine at po
sition 4 substituted with leucine), peptide/MHC complexes showed no de
tectable 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 understandin
g was revealed by studying the extent to which activation by variant p
eptides was dependent on CD8. Our data indicate that resistance to ant
i-CD8 mAb blocking correlates with strong binding affinity between sTC
R and MHC/peptide complexes. These data suggest that, for the activati
on of CTL function, the absolute level of intrinsic affinity of TCR fo
r MHC/peptide ligand is not a single critical determinant, but rather,
that activation is governed by the compound influence of several fact
ors, which ensures a minimum threshold of intracellular triggering is
reached to elicit the response.