Multiple HLA-DR antigens: detection with monoclonal antibodies and translation in vitro

L203 and L227 are mouse monoclonal antibodies specific for human HLA-DR antigens. Their reactivity with multiple, structurally different, HLA-DR antigens was examined by using radioiodinated human lymphoblastoid cells and cell lines, heterozygous or homozygous at the HLA-D locus. Antibody L203 precipitates DR antigens composed of 34,000 Mr heavy chains (alpha), and 28,000-29,000 Mr light chains (beta). Antibody L227 recognizes two other species of DR antigens. Their heavy chains have similar molecular weights of 34,000 but their light chains are different, one (beta) being 28,000-29,000 Mr and the other (beta') 23,000-25,000 Mr. Whereas L203 is directed against a combinatorial determinant generated by both DR chains, L227 is able to recognize each of the two light chains alone and reprecipitate them after their separate elution from sodium dodecyl sulfate gels. Poly(A)-containing mRNA was isolated from Raji cells and translated in vitro by microinjection in Xenopus oocytes. The oocytes translated and fully assembled all the DR molecules recognized by L203 and L227 antibodies.