The complement system is involved in the host defence by recognition and elimination of potentially harmful exogenous and endogenous structures from the human body. Activation of complement may also promote inflammatory reactions and cause tissue damage if adequate control is not provided by the complement regulatory proteins. Significant amounts of biologically active products arising from complement activation have been detected in patients with rheumatoid arthritis.

To investigate the role of complement cascade in juvenile idiopathic arthritis.

12 serum samples and 2 samples from synovial fluid were obtained from 2 individuals with juvenile idiopathic arthritis (JIA). The complement kit for assessment of classical, alternative and MBL pathway activity was developed by the EU consortium and prepared centrally at Wieslab (Sweden).

The samples of synovial fluid showed a deficiency in the classical, alternative and MBL pathway of the complementb system. The results in the sera were normal.

Complement system might play a major role in the development of joint effusion in JIA.