Specific interleukin-1 inhibitor in serum and urine of children with systemic juvenile chronic arthritis.

Interleukin-1 (IL-1) activity and inhibition were studied in serum and urine from nine patients with systemic juvenile chronic arthritis (S-JCA). In afebrile patients IL-1 activity was normal or high. Serum from two afebrile S-JCA patients taken during a period of severe disease activity had an enhancing effect on the activity of exogenous IL-1. Secondary amyloidosis subsequently developed in one of these patients. In contrast, in febrile patients' serum and urine IL-1 activity was low, apparently reflecting the presence of a strong inhibitor of IL-1 activity measured by the inhibition of prostaglandin E2 production by synovial cells. This inhibition was greatest at the time of peak temperature, suggesting the possibility of feedback regulation during fever. This novel identification in S-JCA of a specific IL-1 inhibitor that competes at the IL-1 receptor level may be an important step in the understanding of the pattern of fever and the evaluation of disease in patients with S-JCA.