Studies of the third component of complement in synovial fluid from arthritic patients. II. Conversion and its relation to total complement

Plasma and synovial fluid from arthritic patients were studied with antigen–antibody crossed electrophoresis for the conversion of C3. When present, C3 conversion was estimated planimetrically. The material included patients with rheumatoid arthritis and systemic lupus erythematosus as well as patients with non-rheumatoid arthritis.

C3 conversion was not found in plasma from any of the patients studied.

In non-rheumatoid synovial fluids there was no conversion in five and less than 10% in four of the samples. In rheumatoid synovial fluids C3 conversion proved significantly (P<0·01) more pronounced, the degree of conversion exceeding 10% in fourteen out of twenty-three cases. An inverse relationship was found in synovial fluid between the degree of C3 conversion on the one hand, and the total complement activity or the C3 concentration on the other.