The isolation of immune complexes containing IgM rheumatoid factor and recovery of IgG rheumatoid factor from the complexes.

IgG with rheumatoid factor activity has been recovered from immune complexes containing IgM rheumatoid factor. This was done by passing serum from patients with rheumatoid arthritis through an immunoadsorbent column of the F(ab')2 fragment of rabbit anti-human mu chain. The recovered IgM was analysed by radioimmunoassays for IgM and IgG rheumatoid factors before and after sucrose density gradient centrifugation at neutral and acid pH. It is considered that the method may be generally applicable for the isolation of immune complexes containing IgM antibodies.