Detection of circulating immune complexes by PEG precipitation combined with ELISA

An assay to detect circulating immune complexes is described and exemplified with serum from SLE and RA patients. The method is based on selective precipitation of immune complexes with PEG followed by a specific ELISA assay to detect the immunoglobulins present in the precipitate. The immunoglobulins of the precipitate were then monitored by their capacity to bind protein A and dDNA. With the PEG-protein A-ELISA procedure immune complexes were detected in 46% of the sera from SLE patients compared with 68% when using the PEG-DNA-ELISA.