BIOCHEMICAL AND FUNCTIONAL-CHARACTERIZATION OF SOLUBLE MULTIVALENT MHC L(D) FC-GAMMA-1 AND L(D)/FC-MU CHIMERIC PROTEINS LOADED WITH SPECIFIC PEPTIDES/

Central to the specificity of the immune system is the interaction bet ween the T cell receptor and the major histocompatibility complex (MHC )-peptide ligand complex. To better understand the nature of this inte raction, and to investigate possible avenues for specific therapeutic intervention, we have produced soluble recombinant molecules that can modulate antigen-specific T cells. Our approach involved the construct ion of recombinant murine genes composed of the MHC class I gene H-2L( d) and the Fc portion of immunoglobulin (Ig) heavy chain genes mu or g amma 1. Stable transfectants of these L(d)/Fc gamma 1 and L(d)/Fc mu g enes generated correctly spliced transcripts and were capable of secre ting chimeric protein. Immunoprecipitation analyses demonstrated the p resence of chimeric L(d)/Fc gamma 1 and L(d)/Fc mu monomers of approxi mately 69 kDa and 90 kDa, respectively, as well as chimeric dimers und er nonreducing conditions. The capacity of L(d)/Ig molecules to bind s pecific peptide ligands was demonstrated using radiolabeled peptides o r with monoclonal reagents that specifically identify peptide-induced conformational changes in the L(d) ligand binding site. Soluble divale nt L(d)/Fc gamma 1 molecules were loaded with the murine cytomegalovir us-derived peptide and other L(d)-specific peptide ligands and subsequ ently isolated and purified. Peptide-loaded L(d)/Fc gamma 1 molecules were capable of inhibiting the response of class I-restricted T cells in vitro in a peptide-specific fashion. The development of soluble mul tivalent chimeric proteins that possess unique properties of both the MHC class I and Ig molecules provides a valuable reagent for the study of potential mechanisms of in vitro and in vivo immune modulation.