Elevated levels of IL-37 correlate with T cell activation status in rheumatoid arthritis patients

Objective: To assess the association between serum levels of IL-37 in rheumatoid arthritis patients and percentage of peripheral blood T lymphocytes expressing the activation marker CD26 and investigate their correlation with disease activity. Methods: The study included 48 rheumatoid arthritis patients and 42 age and sex matched healthy controls. Serum levels of IL-37 were determined using enzyme linked immunosorbent assay while percentage of CD3(+)CD26(+)T cells in peripheral blood mononuclear cells was assayed using flowcytometry. Results: Serum levels of IL-37, as well as the percentage of CD3(+)CD26(+)T cells, were significantly higher in rheumatoid arthritis patients than in healthy controls. Also, serum IL-37 levels were higher in patients with severe disease activity than patients with moderate and low disease activity. In rheumatoid arthritis patients, both serum levels of IL-37 and percentage of CD3(+)CD26(+)T cells correlated with disease activity (DAS28), C reactive protein levels and erythrocyte sedimentation rate. In addition, serum levels of the anti-inflammatory cytokine IL-37 positively correlated with the percentage of CD3(+)CD26(+)T cells in peripheral blood of rheumatoid arthritis patients. Conclusion: Our results indicate a strong correlation between serum levels of IL-37 and frequency of activated T cells in peripheral blood of rheumatoid arthritis patients. Our results suggest that in an active disease status, activated T lymphocytes may be a contributing source to the elevated levels of IL-37 trying to down-regulate the active inflammatory process.