title: A alpha and A beta class II I-A determinants of antigen-specific T-helper factor and its antigen-nonbinding chain.
abstract: Antigen-specific T-helper factor (ThF) of CBA (H-2k) origin in the picryl (TNP) contact sensitivity system (Mr 60-70 kDa) was reduced with dithiothreitol under mild conditions. Affinity chromatography on antigen yielded an antigen-binding chain (Mr 20-30 kDa) and an antigen-nonbinding chain (Mr 40-50 kDa). Both chains were glycoproteins and were bound by lentil lectin. Affinity chromatography on anti-I-A monoclonal antibodies showed that I-A determinants occurred on the complete molecule and on the antigen-nonbinding, but not on the antigen-binding, chain. In contrast, five different monoclonal antibodies to I-E alpha failed to absorb ThF. Moreover, the complete molecule and the I-A+ antigen-nonbinding chains had determinants of the alpha and beta chains of I-A and conformational determinants which are based on both chains. Sequential absorption and elution showed that A alpha and A beta determinants occurred on the same molecular complex. These data suggest a minimal model of ThF as a two-chain disulfide-bonded structure with an antigen-binding chain and a separate I-A+ antigen-nonbinding chain which behaves as a single unit in phosphate-buffered saline and has elements of both A alpha and A beta.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001665:Binding Sites; D000939:Epitopes; D006023:Glycoproteins / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000276:immunology*; D007375:Interleukin-1 / Q000276:immunology*; D008211:Lymphocyte Cooperation; D046911:Macromolecular Substances; D051379:Mice; D008970:Molecular Weight; D011946:Receptors, Antigen / Q000502:physiology*; D014301:Trinitrobenzenes / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D006023:Glycoproteins; D000949:Histocompatibility Antigens Class II; D007375:Interleukin-1; D046911:Macromolecular Substances; D011946:Receptors, Antigen; D014301:Trinitrobenzenes