MEASUREMENT OF THE CHEMOTACTIC COMPLEMENT FRAGMENT C5A IN RHEUMATOID SYNOVIAL-FLUIDS BY RADIOIMMUNOASSAY - ROLE OF C5A IN THE ACUTE INFLAMMATORY PHASE

Evidence suggests that complement is activated in rheumatoid joints. A sensitive radioimmunoassay for the activation fragment of C5, C5a, which is a potent chemoattractant for neutrophils, was therefore developed. A mean CSa concentration in 22 rheumatoid joint fluids of about 2-5xlO-9 mol/l was found. This concentration of C5a is sufficient to induce two of the characteristic features of the acute inflammatory phases of rheumatoid arthritis: neutrophil accumulation and microvascular plasma protein leakage. In animal models it has been shown that C5a is a potent inducer of inflammatory oedema by a neutrophil dependent mechanism. A striking feature of the acute inflammatory phases of rheumatoid arthritis is the appearance ofhigh numbers of neutrophils in the synovial fluid. It is suggested that CSa might have a role in mediating neutrophil accumulation and, as a consequence, may be important in acute joint swelling and pain.