Circulating immune complex levels measured by new ELISA kits utilizing monoclonal anti-C1q and anti-C3d antibodies correlate with clinical activities of SLE but not with those of RA.

The authors studied sera from both patients with SLE and from those with RA to evaluate clinical usefulness and significance of circulating immune complexes (CIC) detected with new ELISA kits utilizing monoclonal anti-C1q and anti-C3d antibodies. CIC values of patients with SLE significantly correlated to severity of disease activities evaluated by clinical symptoms and laboratory tests, especially for serum complement levels. Since substances detected with the ELISA kits were closely related to serum complement components, it was determined that a direct relationship exists between clinical activities and CIC values appearing in SLE patients with hypocomplementemia. In RA patients, CIC values did not correlate to clinical activities evaluated by Lansbury's index, anatomical bone damage with X-ray or functional assessment of activities of daily living, but did significantly correlate to levels of IgM-RF, serum IgG concentrations and some markers of systemic inflammation. Detection of IC after fractionation of RA sera revealed a broad range of molecular sizes detectable with the ELISA kits, which indicated that CIC in vivo were heterogenic and complicated in formation, degradation and interaction with serum complements.