Inhibition of an allospecific T cell hybridoma by soluble class I proteins and peptides: Estimation of the affinity of a T cell receptor for MHC

To investigate the molecular basis of the interaction between the T cell receptor and the MHC class I antigen in an allogeneic response, a soluble counterpart of the murine class I molecule, H-2K^b, was genetically engineered. Cells secreting this soluble molecule, H-2K^b/Q10^b, inhibited stimulation of an H-2K^b-reactive T cell hybridoma by cells transfected with H-2K^bm10, a weak stimulus, but not by H-2K^b- or H-2K^bm6-transfected cells. Soluble purified H-2K^b/Q10^b protein also blocked T cell stimulation. In addition, a peptide from the wild-type H-2K^b molecule spanning the region of the bm10 mutation specifically inhibited activation of the T cell hybridoma by H-2K^bm10 cells, thus suggesting that amino acid residues 163-174 of H-2K^b define a region important for T cell receptor binding. An estimate for the K_d of the T cell receptor for soluble H-2K^b/Q10^b was 10^-7 M, while the K_d for soluble peptide 163-174 was 10^-4 M.