A Clq solid phase microenzymatic assay for the detection of soluble immune complexes.

The solid phase Cl1-binding assay has been adapted to an enzymatic micromethod in which alkaline phosphatase labeled soluble Staphylococcus aureus protein A is used in place of the second antibody. The assay, which is run in microtiter plates, provides a rapid, sensitive (0.030 mg/ml of human heat-aggregated IgG detected) and reproducible method for the measurement of soluble immune complexes in a large number of samples. Soluble immune complexes prepared in vitro with bovine serum albumin (BSA) and anti-BSA antibodies on a wide range of antigen to antibody ratios were all detected with this method. When applied to the screening of unselected patient sera, soluble immune complexes were frequently found in systemic lupus erythematosus (52%) and chronic active hepatitis (57%) and in lower percentages in patients with malignant melanoma (28%), rheumatoid arthritis (30%) and essential mixed cryoglobulinemia (17%).