[Complement fragment C 3d in the plasma of patients with chronic polyarthritis].

Activation of the complement system via immune complex formation plays an important role in the perpetuation of chronic inflammatory disorders. The serum levels of C3 or C4 do not necessarily reflect the actual complement catabolism. By measurement of the long-lived C3 split product "C3d" direct information about complement activation can be obtained. C3d was measured with a modified immunoelectrophoresis technique in EDTA-plasma of 106 patients with rheumatoid arthritis. 36% of them showed significantly elevated C3d levels (mean: 8.93 micrograms/ml). Significant linear correlations were found for C3d with ESR, Lansbury-Index and plasma viscosity.