Intraarticular activation of the complement system in patients with juvenile rheumatoid arthritis.

Analyses of CH50, complement components, properdin factors, and kininogen in synovial fluid of patients with juvenile rheumatoid arthritis revealed evidence of activation of the classic complement pathway in all clinical subgroups. Juveniles with the adult pattern of disease had the greatest incidence of complement abnormalities. Evaluation of individual components by both activity determination and protein measurement showed decreased synovial fluid specific functional activity (activity per microgram protein) to the more marked in synovial fluids with profound depressions of complement activity. These findings provide further evidence that nonfunctional, antigenically intact component protein may remain after complement activation. Radial immunodiffusion measurements of properdin factors and kininogen failed to support their involvement in joint inflammation. Serum complement component measurements by activity but not protein concentration correlated with other parameters or inflammation. Four patients had isolated depressions of serum C2 activity. Immunoglobulin levels, particularly IgA, correlated with some complement measurements and with the sedimentation rate.