A possible role for soluble IL-6 receptor in the pathogenesis of systemic onset juvenile chronic arthritis

Investigation of the agonist and two antagonists to interleukin 6 (IL-6) and their possible role in the pathogenesis of different sub-groups of juvenile chronic arthritis (JCA). Sera of 54 patients and 10 age-matched controls were tested: 20 with pauci-articular JCA, 12 with polyarticular JCA, and 22 systemic JCA. Interleukin 6, soluble interleukin 6 receptor (agonist), soluble gp130 and autoantibodies to IL-6 (antagonist to IL-6) were measured, as well as C-reactive protein as an indicator of disease activity. In addition, during fever two systemic JCA patients were analysed longitudinally for these parameters. There was a significant increase in soluble IL-6 receptor (sIL-6R) concentrations. No difference in the levels of soluble gp130 and autoantibodies to IL-6 in the systemic JCA group was found. In two patients the fever curves corresponded to the IL-6 levels measured. sIL-6R serum concentrations also showed a tendency to follow the fever. The authors have shown that in systemic JCA, the levels of sIL-6R, agonist of IL-6, were increased significantly compared to the other groups, while levels of antagonists to IL-6 were not changed in the face of increased levels of IL-6 in systemic JCA. These results suggest an imbalance of IL-6 homeostasis.