CD4 AUGMENTS THE RESPONSE OF A T-CELL TO AGONIST BUT NOT TO ANTAGONIST LIGANDS

The recognition of peptide variants by the T cell receptor (TCR) has r evealed a wide range of possible responses. Here, using a series of CD 4(+) and CD4(-) variants of the same T cell hybridoma, we find that wh ile the expression of CD4 converts weak agonists into full agonists, n one of the antagonist peptides are efficiently recognized as agonists. Furthermore, in antagonist assays, little difference can be seen in t he response of CD4(+) and CD4(-) T cells. Together with previous work showing a marked difference in stability between TCR binding to agonis t versus antagonist ligands, these data suggest that CD4 engagement oc curs after a TCR-peptide/MHC complex has formed and that it requires a certain minimal half-life of the ternary complex to be fully engaged in signaling.