CORRELATION BETWEEN THE NUMBER OF T-CELL RECEPTORS REQUIRED FOR T-CELL ACTIVATION AND TCR-LIGAND AFFINITY

The number of T cell receptors on CTL clone 2C that are required for r ecognition of various peptide-MHC or superantigen-MHC ligands were mea sured as a function of both the ligand density on target cells and the binding affinity of the TCR. Quantitative inverse correlations were d etermined between the number of TCRs required for recognition and the number of ligands on target cells, and the number of TCR required and the K-a of the TCR for the ligand. We propose and test predictive uses of these relationships to determine the number of endogenous peptide- MHC complexes on a target cell (when TCR affinity is known) or to dete rmine the affinity of the TCR (when the number of ligands is known).