Journal of Clinical Investigation · 1974 · 434 citations · 41 references
Life SciencesImmunologyAutoimmunityClinical ImmunologyImmunopathologyAntibody CharacterizationAntibody-antigen RecognitionAutoantibodiesAutoimmune Disease DiagnosticsDiagnostic ImmunologySystemic Lupus ErythematosusAntigen-antibody Complex FormationImmune Complex DetectionImmune Complex FormationImmunoassay MethodologyPrecipitation ReactionsProtein ComplexesSelective PrecipitationSoluble Antigen - Antibody Interactions
The study reports a sensitive, reproducible method to detect soluble immune complexes in sera from patients with immunopathological disorders. The method uses radiolabeled C1q that binds immune complexes, with free and bound fractions separated by PEG precipitation, exploiting the complexes’ large size and C1q‑binding property. The assay detects as little as 10 µg of aggregated immunoglobulins or 3 µg of soluble IgG‑anti‑IgG complexes, remains sensitive in large antigen excess, and is specific because antigen‑F(ab′)₂ complexes do not precipitate radiolabeled C1q.
A sensitive and reproducible procedure for the detection of soluble immune complexes in sera from patients with various immunopathological disorders is reported. Radiolabeled C1q is reacted with sera containing immune complexes. Separation of free from complex bound [125I]C1q is achieved by selective precipitation with polyethylene glycol (PEG). The method is based on both the large molecular size and the C1q-binding property characterizing immune complexes. The minimal amount of aggregated immunoglobulins thus detected is about 10 μg and that of soluble human IgG-anti-IgG complexes is about 3 μg of complexed antibody. Some immune complexes formed in large antigen excess (Ag2Ab) can still be detected by this radiolabeled C1q binding assay. The specificity of the radiolabeled C1q binding test was documented by the inability of antigen-F(ab′)2 antibody complexes to lead to a precipitation of [125I]C1q in PEG.
41