Characterization of a Novel Class Ib Molecule of the Rat : Preparation of Specific Antibodies with the Multiple Antigen Peptide System and a Recombinant Protein Produced by the Prokaryotic Expression System

The functional significance of class Ib MHC genes and their products is still enigmatic, but they show structural similarity to classical transplantation antigens in that they are composed of three extracellular domains: a peptide binding domain, an immunoglobulin supergene family constant (Ig-C) domain and a noncovalently linked β2 m. We have isolated class I cDNA clones from a rat thymus cDNA library. In this study, we selected a novel cDNA clone containing unique nucleotide sequences based on partial nucleotide sequences. Specific antibodies against the class Ib molecule were produced using two methods, a synthetic multiple antigenic peptide (MAP) system, and injections of a recombinant protein made by a prokaryotic expression system. The antibodies reacted specifically with the immunogens and with cultured cell lines transfected with the relevant cDNA in mammalian expression vectors. In normal rat tissues and cells, this novel class I molecule was expressed primarily by the cells in the thymus. A possible functional significance of the thymus specific class Ib molecule is discussed