Objective: To compare plasma levels of interleukin-1 receptor antagonist (IL-1Ra), soluble IL-1 receptor type I (sIL-1RI), and soluble IL-1 receptor type II (sIL-1RII) in patients with chronic polyarthritis, and to establish correlations between levels of these naturally occurring IL-1 inhibitors and indices of disease activity and joint destruction.
Methods: Levels of IL-1Ra, sIL-1RI, and sIL-1RII were measured in plasma samples from patients with chronic polyarthritis, using specific radioimmunoassays. Levels were correlated with indices of disease activity and joint destruction.
Results: Plasma levels of IL-1Ra, sIL-1RI, and sIL-1RII were significantly higher in polyarthritis patients than in controls. IL-1Ra levels correlated positively with all indices of disease activity and joint destruction (P < 0.0001). In contrast, sIL-1RII levels correlated negatively with indices of joint destruction, such as the Larsen score in the wrist (P < 0.04). Interestingly, sIL-1RII levels were higher in patients with nondestructive arthritis (Larsen score < or =1) than in patients with destructive arthritis. Levels of sIL-1RI did not correlate with indices of disease activity or joint destruction.
Conclusion: The present findings indicate that increased levels of IL-1Ra, a natural antiinflammatory acute-phase protein, may reflect increased production and activity of IL-1. In contrast, endogenous sIL-1RII, unlike sIL-1RI, may constitute a natural antiinflammatory factor in chronic polyarthritis. These differences should be taken into account when these antiinflammatory molecules are considered as prognostic markers or for therapeutic use.