Complexed autoantibodies in patients with juvenile connective tissue diseases, isolated by rate-zonal ultracentrifugation.

Selected sera from one patient with systemic lupus erythematosus, two with mixed connective tissue disease, one with dermatomyositis, one with progressive systemic sclerosis and one with juvenile rheumatoid arthritis were investigated for autoantibodies after fractionation by computerized rate-zonal ultracentrifugation. Anti-Smith antibodies sedimented in an area from 6–11 S and anti-ribonucleoprotein from 6–13 S. IgG anti-IgG and IgG antinuclear antibodies (ANA) were present in free or complexed form in the 6–13 S area. IgM ANA occurred as 7 S IgM in patients with systemic lupus erythematosus and mixed connective tissue disease, whereas IgM ANA sedimented in the 19 S area in patients with dermatomyositis and progressive systemic sclerosis. Complexes containing IgG anti-IgG and ANA, positioned in the 6–13 S area are likely to play a significant role in the pathogenesis of systemic lupus erythematosus and mixed connective tissue disease.