Detection and quantitation of circulating immune complexes in arterial blood of patients with rheumatic disease

We developed antigen-nonspecific enzyme-linked immunoassays (ELISA) to quantitate IgG-C3- and IgM-C3-containing circulating immune complexes (CIC) in venous and arterial blood from rheumatic disease patients. Standards were diethylaminoethyl (DEAE)-purified, heat-aggregated IgG incubated with fresh human serum (for IgG-C3 CIC) and IgM rheumatoid factor-rich serum incubated with reduced, alkylated IgG and then with fresh human serum (for IgM-IgG-C3 CIC). Venous serum and plasma IgG-C3 and IgM-C3 CIC correlated closely (P < 0.01). Rheumatoid arthritis (RA) and systemic lupus erythematous (SLE) patients had elevated levels of venous IgM-C3 CIC (P < 0.0001) but not IgG-C3 aIC; patients with vasculitis, inflammatory rheumatic diseases, or noninflammatory rheumatic diseases had mean values similar to normal individuals. Venous IgG-C3 and IgM-C3 CIC did not correlate. Paired venous and arterial samples from 16 rheumatic disease patients averaged comparable amounts of IgG-C3 and IgM-C3 CIC, respectively; venous and arterial IgM-C3 CIC levels in patients significantly exceeded normals (P < 0.01) Venous and arterial IgG-C3 CIC levels correlated closely (P < 0.01) as did venous dnd arterial IgM-C3 levels (P < 0.05). Thus, arterial CIC offered no advantage over venous determinations for rheumatic disease patients. IgM-C3 CIC were elevated in patients with RA and SLE when IgG-C3 CIC were not. Ig isotype-specific CIC quantitation may be useful for certain rheumatic diseases.