The in-vivo metabolism of C3 in ankylosing spondylitis.

Turnover studies with radioactively labelled C3 were performed in 7 patients with ankylosing spondylitis and in 14 healthy individuals . As a group the patients had a moderately higher fractional catabolic rate of C3 than the controls. A possible explanation is that the complement system is activated by immune complexes. The serum levels of C3 were high. The hypercatabolism was therefore more than compensated for by an increased synthesis rate.