THE EFFICIENCY OF ANTIGEN RECOGNITION BY CD8(+) CTL CLONES IS DETERMINED BY THE FREQUENCY OF SERIAL TCR ENGAGEMENT

Using H-2K(d)-restricted CTL clones, which are specific for a photorea ctive derivative of the Plasmodium berghei circumsporozoite peptide Pb CS252-260 (SYIPSAEKI) and permit assessment of TCR-ligand interactions by TCR photoaffinity labeling, we have previously identified several peptide derivative variants for which TCR-ligand binding and the effic iency of Ag recognition deviated by fivefold or more. Here we report t hat the functional CTL response (cytotoxicity and IFN-gamma production ) correlated with the rate of TCR-ligand complex dissociation, but not the avidity of TCR-ligand binding. While peptide antagonists exhibite d very rapid TCR-ligand complex dissociation, slightly slower dissocia tion was observed for strong agonists, Conversely and surprisingly, we ak agonists typically displayed slower dissociation than the wild-type agonists, Acceleration of TCR-ligand complex dissociation by blocking CD8 participation in TCR-ligand binding increased the efficiency of A g recognition in cases where dissociation was slow. In addition, perma nent TCR engagement by TCR-ligand photocross-linking completely abolis hed sustained intracellular calcium mobilization, which is required fo r T cell activation, These results indicate that the functional CTL re sponse depends on the frequency of serial TCR engagement, which, in tu rn, is determined by the rate of TCR-ligand complex dissociation.