Circulating immune complexes in ankylosing spondylitis.

Circulating immune complexes were determined in the sera of patients with ankylosing spondylitis using a polyethylene glycol precipitation laser nephelometer technique. Positive results were obtained in 52% of sera from patients with active disease, but only in 20% from those in inactive stages. The immunoglobulin/complement protein ratio differed from that seen in rheumatoid arthritis and in systemic lupus erythematosus, due to the relatively larger amounts of C3 and C4 present in the immune complexes. These findings indicate that circulating immune complexes in ankylosing spondylitis may not be of pathogenetic significance because of their degree of solubilization.