Clinical significance of serum and synovial fluid complement component activities in juvenile rheumatoid arthritis

ABSTRACT

Functional activity of the total hemolytic complement [CH50] as well as the activity of four of the complement components [C1, C4, C2, and C9] were examined [using the haemolytic assay] both in the synovial fluid and sera from 25 patients with juvenile rheumatoid arthritis [JRA]. The clinical subgroups of the disease were as follows 12 patients had a polyarticular onset, 10 patients had polyarticular onset; while 3 patients had systemic onset. The incidence of seropositivity in these patients was 32%. Among the seurm four complement component activities measured in this study, C1 was not elevated, C4 and C2 were moderately elevated and C9 was markedly supernormal. The higher C9 activity observed in the patients correlated well with blood sedimentation index. On the other hand, when synovial fluids were examined for CH50 and component activities of complement, the specimens could be divided into two groups according to the level of C4 Group 1 [11 patients] had titres of 10,000 u/ml or less and Group 11 [14 patients] had titres greater than 10,000 u/ml. Group 1 patients tended to be females, to have a significantly older age at onset, and to have polyarticular disease; only three of the eleven patients in group 1 were seronegative. Group 11 tended to have more males, than females, and to contain patients with pauciarticular disease and all were serongeative. The activities of C9 in serum and synovial fluid were highly correlated in the 25 paired specimens. This may indicate that there is an equilibrium between serum and synovial fluid C9 [which is alpha 2-globulin and the smallest protein among the complement components]; and the slope of the regression line of that correlation may represent the state of permeability of synovial membranes in such patients. In conclusion, the whole haemolytic complement activity as well as the complement component activities were depressed in the synovial fluid of patients with JRA, while the serum complement component activities were normal or elevated. Moreover, synovial fluid levels were profoundly depressed irrespective to seropositivity. These changes can result from complement hypercatabolism occurring within the rheumatoid joint space which, therefore, be reflected in normal serum levels of complement components