Different patterns of C3 and C4 activation in the varied types of juvenile arthritis

Quantitative assays for C3 and C4 activation were carried out simultaneously on blood from children with varied types of juvenile arthritis. Factor VIII-related antigen was also measured as an indicator of vascular damage. In active systemic juvenile arthritis, the C4d/C4 ratio was frequently elevated and was usually associated with elevated C3d/C3 ratios and elevated concentrations of factor VIII-related antigen. Children with chronic polyarticular arthritis, no matter which forms of onset they had had, also had increased levels of the C4d/C4 ratio, C3d/C3 ratio, and factor VIII-related antigen, but these were less consistent and were not associated with each other. In contrast, in pauciarticular arthritis there was a uniquely isolated increase in the C3d/C3 ratio. This work implies that there are different mechanisms responsible for complement activation in the different types and at different stages of juvenile arthritis.