Antigammaglobulin (rheumatoid factor) activity of human IgG subclasses

A sensitive radioimmunoassay has been applied to the study of rheumatoid factor activity of IgM and IgG subclasses in serum and synovial fluid of patients with rheumatoid arthritis. Although rheumatoid factor activity was found in all four subclasses, its distribution was not the same as that of the total subclasses in normal sera. Results are discussed in relation to the possible clinical value of measuring IgG rheumatoid factor in sera and synovial fluids of patients with rheumatoid arthritis.