Role of IgM & IgA rheumatoid factors in complement activation in patients with juvenile rheumatoid arthritis.
We studied the relationship between the degree of complement activation in juvenile rheumatoid arthritis (JRA) with the levels of circulating IgM and IgA rheumatoid factors (RF). Forty children with JRA and 25 matched controls were included in the study. Levels of C3d (a degradation product of complement component C3), circulating immune complexes (CICs), IgM RF and IgA RF were measured by ELISA. Levels of C3d, CICs, IgM RF and IgA RF were elevated in patients with JRA as compared to controls. Levels of C3d had a linear relationship with levels of CICs (P < 0.05) but not with levels of circulating IgM RF and IgA RF. Thus, complement activation occurs in children with JRA and is associated with raised levels of CICs but not with levels of circulating IgM and IgA RF. Circulating IgM and IgA RF have little, if any, role in complement activation observed in patients with JRA.