Complement-activating rheumatoid-factor-containing complexes in patients with rheumatoid vasculitis

The role of complement and rheumatoid factor in immune complexes was examined in patients with a variety of rheumatic diseases. This was done by assessing the amount of rheumatoid factor (RF) bound from sera by F(ab)2 anti-C3 attached to a solid matrix. High levels of RF bound to C3 were detected in patients with rheumatoid arthritis complicated by vasculitis but rarely and in lower levels in patients with synovitis, ankylosing spondylitis, and systemic lupus erythematosus. The activity was bound to anti-C3 through anti-C3 antibodies because little was bound by normal F(ab)2 and was evidently complexed in the sera before in-vitro testing, since it was precipitated by 2 . 5% polyethylene glycol and sedimented with high molecular weight material on sucrose density gradient ultracentrifugation. It is considered that RF-containing complexes are present in vasculitic sera and have the potential to bind complement in vivo.