Production and characterization of monoclonal antibodies recognizing the alpha-chain subunits of human ia alloantigens.

Two monoclonal antibodies, TAL-1B5 and TAL-3C3, specific for human Ia alpha-chain subunits have been produced by fusing P3/NSI/1-Ag4-1 mouse myeloma cells with spleen cells from a BALB/c mouse immunized with purified alpha-chains. Specificity for the alpha-chain subunits was initially established using a solid-phase radioimmunoassay. Indirect binding assays demonstrated that TAL-1B5 bound strongly to all human B lymphoblastoid lines tested and to CLLs, but only weakly to PBL-B cells and not to PBL-T cells or the T-cell lines Molt 4 and HSB-2. TAL-3C3 bound only weakly to B lymphoblastoid lines and not to CLLs or PBL-B cells. From 125I cell surface-labelled lysates TAL-1B5 immunoprecipitated a 33,000(alpha):28,000(beta) Ia dimer, but TAL-3C3 failed to immunoprecipitate cell surface molecules. Under denaturing conditions, however, both TAL-1B5 and TAL-3C3 immunoprecipitated the 33,000 alpha-chain subunit. Competitive inhibition studies demonstrated that both monoclonal antibodies recognize the same or spatially related alpha-chain antigenic determinants with some slight cross-reactivity against beta-chains. 2D-NEPHGE/SDS-PAGE analysis of TAL-1B5 immunoprecipitates from [35S]-methionine biosynthetically labelled cells revealed the presence of a number of alpha-chain spots in association with beta-chain products of three previously described loci (beta-1, beta-2, beta-3) suggesting that this antibody recognizes an antigenic site common to those human Ia alpha-chains so far identified.