A solid-phase assay for circulating immune complexes using monoclonal rheumatoid factors and peroxidase-linked protein A.

A solid-phase monoclonal rheumatoid factor (mRF) assay for circulating immune complexes (IC) is described. Microtiter plates are coated with mRF, serum diluted 1 : 40 is added, and complexed IgG is detected with protein A coupled to peroxidase. Selective binding was obtained with aggregated human gamma-globulin and soluble IC prepared in vitro. Sucrose density gradient ultracentrifugation studies indicate that mRF binds intermediate-size IC (between 7S and 19S). Abnormal levels of IC were found in 78% of sera from patients with rheumatoid arthritis, 67% with systemic lupus erythematosus, and 87% with subacute bacterial endocarditis.