title: A solid-phase radioimmunoassay for the detection of nRNP immune complexes.
abstract: We developed a solid-phase radioimmunoassay for complement (C)-fixing nuclear ribonucleoprotein (nRNP):anti-nRNP immune complexes (nRNP ICs). The assay was based on the ability of the C-fixing nRNP ICs to bind strongly to immobilized F(ab')2 anti-C3. The extent of binding was quantified by incubating the C-fixing nRNP ICs bound to anti-C3 with 125I-labeled anti-nRNP-specific IgG. The interaction between anti-C3 and C-fixing nRNP ICs was rapid, time- and concentration-dependent and sensitive over a broad range of nRNP IC concentrations in an antigen-antibody ratio of 8 : 1 (9.8-5000 ng of human aggregated IgG equivalent per ml). We found that the assay also detected an immunoreactive U1-RNP antigen in Sm : anti-Sm immune complexes but did not detect SSA : anti-SSA immune complexes. The assay was preliminary applied for serum samples obtained from patients with mixed connective tissue disease (MCTD), and elevated concentrations of nRNP immune complexes were found in 3 out of 5 patients with MCTD. This assay appears to be applicable to the detection and quantification of circulating nRNP ICs in patients with MCTD.
mesh_terms: D000328:Adult; D000936:Antigen-Antibody Complex / Q000032:analysis*; D000941:Antigens / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology*; D003176:Complement C3 / Q000276:immunology; D003168:Complement Fixation Tests; D004306:Dose-Response Relationship, Immunologic; D005260:Female; D006801:Humans; D008875:Middle Aged; D008947:Mixed Connective Tissue Disease / Q000276:immunology*; D011863:Radioimmunoassay / Q000379:methods; D012261:Ribonucleoproteins / Q000276:immunology*
chemical_list: D000936:Antigen-Antibody Complex; D000941:Antigens; D001323:Autoantibodies; D001324:Autoantigens; D003176:Complement C3; D012261:Ribonucleoproteins