IgM rheumatoid factor and low molecular weight IgM. An association with vasculitis

The occurrence of IgG rheumatoid factor (IgG RF) and low molecular weight IgM (7S IgM) has been studied in the sera of rheumatoid patients with and without vasculitis. IgG RF was found in 67% of patients with vasculitis and in only 9% of patients without vasculitis. 7S IgM was found in 80% of patients with rheumatoid vasculitis and only 18% of patients without vasculitis. Both IgG RF and 7S IgM occurred simultaneously in 60% of patients with vasculitis and 6% of patients without vasculitis. Techniques for demonstrating IgG RF and 7S IgM in serum are described. The findings reported suggest that immune complexes containing IgG RF and possibly low‐molecular weight IgM may be involved in the pathogenesis of rheumatoid vasculitis.