Objective: To evaluate the association of the level of soluble serum interleukin-2 receptor (sIL-2R) with disease activity and response to therapy in patients with rheumatoid arthritis (RA).
Methods: The sIL-2R levels of 148 patients with refractory RA were determined by enzyme-linked immunosorbent assay. This parameter was correlated with other clinical observations obtained during a prospective, randomized, placebo-controlled trial of methotrexate, sponsored by the Cooperative Systematic Studies of Rheumatic Diseases consortium. Using statistical modeling, the usefulness of sIL-2R as a measure of disease activity and a predictor of outcome was evaluated.
Results: The mean sIL-2R level in all RA patients was markedly elevated compared with that in normal control subjects, and decreased significantly during the trial. There was no correlation of the sIL-2R level and the joint pain/tenderness count either at study entry or study end. There was a significant correlation of the sIL-2R level and the erythrocyte sedimentation rate, both at study entry and study end. A multiple linear regression model showed that treatment with methotrexate, but not the sIL-2R level or the change in sIL-2R level, predicted a change in joint count. A stepwise multiple logistic regression model defined no significant predictive information for outcome for the level of sIL-2R at study entry.
Conclusion: After controlling for the simultaneous effects of other important clinical variables, the level of sIL-2R does not appear to predict the response to methotrexate in patients with refractory RA. Further analysis of cohorts of patients with earlier RA needs to be performed.