GENETIC-RECOMBINATION IN THE ALPHA-2 DOMAIN OF THE E-ALPHA CHAIN YIELDS AN ED MOLECULE WITH ALTERED T-CELL ACTIVATION

We have used a novel T cell selection strategy to isolate a mutant of an H-2d/f murine macrophage line defective in its ability to present antigen to some E(d)-restricted helper T cells. This mutant has an amino acid substitution in the alpha-2 domain of the E(d) molecule. The mutation changes the sequence at codon 177 from ACC to CAC, which results in a threonine to histidine substitution and appears to be the first in vitro mutation to have arisen by genetic recombination. Even though the mutation is distal to the proposed antigen-binding groove, it affects antigen presentation, presumably by altering the scaffolding for the antigen-binding groove. This type of mutant might not be readily isolated using other selection techniques.