Correlation between IgG class of rheumatoid factors, immune complexes and C-reactive protein in human sera containing RF.

We measured the concentration of three immunoglobulin classes of rheumatoid factors (Ig-RFs), C3d binding IgG immune complex (C3d-IC), C1q binding IgG immune complex (C1q-IC) and C-reactive protein (CRP) in 74 samples of human sera with high levels of RF (24.0~2350.0IU/ml). In sera with high levels of C3d-IC (>15.0μg/ml), there was a positive correlation between the levels of CRP and the IgG-RF, but there was no correlation between the levels of CRP and the immune complexes (C3d-IC and C1q-IC). And then, there was a positive correlation between the levels of CRP and IgG-RF or C3d-IC and IgG-RF when the levels of C1q-IC in patients sera were higher than 80.0μg/ml. However, there was no correlation between the levels of CRP and C1q-IC in these patients sera containing high levels of both C3d-IC and C1q-IC. These results indicated that the determination of C3d-IC, C1q-IC, IgG-RF and CRP in human sera containing RF denote different implications as inflammatory indexes on progression of rheumatoid arthritis and other autoimmune diseases.