A Simple Light-scattering Method for Detecting Soluble Immune Complexes in Human Serum

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Abstract
A simple assay based on molecular light scattering was developed to detect soluble immune complexes. In this assay the percentage of relative light scattering (% RLS) caused by complexes in buffer containing polyethylene glycol 6000 (PEG) was measured with a laser nephelometer. In low concentrations of PEG (3%-5%), IgG-anti-IgG complexes formed in antigen excess scattered light more effectively than those formed in antibody excess or equivalence. Since normal serum proteins caused minimal %RLS at 3%-5% PEG, we expanded this assay to screen patient sera. For each test, the serum was used at a 1:20 dilution. The results were expressed by the defined parameter Δ%RLS = (Σ%RLS 3%-5% PEG - Σ%RLS 0%-2% PEG). For 58 normal sera Δ%RLS = 15.4%±11.3%, while for 12 sera from patients who had systemic lupus erythematosus and hypocomplementemia, Δ%RLS = 40.5%±20.0% (P<0.001). In a comparative study of 18 sera positive for immune complexes in the Clq deviation assay, 12 were positive by %RLS.

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