CELL-SURFACE EXPRESSION OF CLASS-II MHC PROTEINS BOUND BY A SINGLE PEPTIDE

On normal cells, the peptide-binding grooves of class II MHC proteins contain a wide spectrum of peptides. For some purposes, however, it wo uld be helpful to have cells bearing class II proteins engaged by only one peptide species. In an attempt to make such cells we constructed a gene for a MHC class Il beta-chain, IA beta(b), covalently linked to a peptide, E alpha 52-68, which is known to bind to the peptide-bindi ng groove of IA(b). This gene, together with the gene for IA alpha(b), was transfected into B lymphoma cells and fibroblasts. The IA(b)-E al pha complex was expressed on the surfaces of these cells where it coul d be recognized by a mAb and T cells specific for IA(b) plus E alpha 5 2-68. Most of the peptide on fibroblasts remained covalently attached to the IA(b) beta-chain, but the covalent linker and/or peptide were d egraded to some extent on B lymphoma cells. Nearly all of the IA(b) ex pressed by transfected fibroblasts was occupied by the E alpha peptide . Of 16 IA(b)-reactive T cell hybridomas, only 3 could respond to the IA(b)-E alpha complex on fibroblasts, confirming the idea that recogni tion of MHC may often involve recognition of the peptides bound to the MHC as well.