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

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.

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.

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.

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.