Detection of immune complexes and their relationship to rheumatoid factor in a variety of autoimmune disorders

The sera of patients with adult rheumatoid arthritis (RA), juvenile rheumatoid arthritis (JRA), systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) were employed together with sensitive radioimmunoassays to examine the relationship between immune complexes detected by three methods and the IgM, IgA and IgG classes of rheumatoid factors (RF). Compared to the controls, significantly increased concentrations of RF and immune complexes were detected for every patient group except JRA. Increased concentrations of IgA RF, IgG RF and immune complexes detected by the ClqBA and the ClqSP were strongly associated with the presence of IgM RF. Significant correlations were noted between RF (especially IgG and IgM) and immune complexes (detected by both the ClqBA and the ClqSP) for patients with RA, SLE and MCTD. These studies suggest that RF may be partially involved in the formation of the immune complexes detected by Clq-binding assays and demonstrate the need for further clarification of the constituents of the immune complexes detected in each disease.