Detection of IgG Aggregates or Immune Complexes Using Solid-Phase C1q and Protein A-Rich Staphylococcus aureus as an Indicator System

A radioimmunoassay for detection of Clq-binding IgG aggregates and antigen-IgG antibody complexes is described The assay makes use of solid-phase Clq and ³²p-labelled protein A-rich Stphylococcusaureus as an indicator system. Both 19S and heavier IgG aggregates that fixed Clq were detected The sensitivity of the assay permitted detection of heavy (19–25S) IgG aggregates at a concentration of 8 μg/ml or less. The results indicated that detection of IgG in this assay is dependent on the degree of IgG polymerization and the molar ratio between the solid-phase Clq and the IgG polymers. Albumin-anti-albumin complexes, preformed at equilibrium with antibody to antigen molar ratios of 2:1 to 3:1 and at antigen concentrations of 25 to 40 μ g/ml. were also detectable using the described radioimmunoassay