Circulating immune complexes in patients with ankylosing spondylitis.

EDTA plasma samples from 13 patients with ankylosing spondylitis (AS) were fractionated on Sephadex G-200 and the quantities of C3 and IgG within the first protein peak determined by a sensitive haemagglutination-inhibition assay. Seven patients with AS had G3 detectable in the first peak and this was associated with an increased concentration of IgG in the corresponding fraction. These 7 patients had more active disease but did not have more peripheral arthritis. Our results indicate that circulating immune complexes capable of initiating complement activation are present in the circulation of patients with ankylosing spondylitis.