Interleukin-32 a Proinflammatory Cytokine in Rheumatoid Arthritis

Objective: To investigate the expression of Interleukin (IL)-32 in the synovial tissue of patients with rheumatoid arthritis (RA) and to determine whether the expression of IL-32 is related to that of other proinflammatory cytokines, specifically tumor necrosis factor (TNF) α and IL-18, and to the degree of joint inflammation. Methods: Biopsy specimens of knee synovial tissue either without synovitis or with moderate or severe synovitis (n=5, 4, and 13, respectively) were obtained from 22 patients with active RA. Paraffin-embedded, snap-frozen sections were used for immmuno-histochemical detection of IL-32. TNF-α was measured in the serum (S) using RIA technique, while IL-18 was measured in both the S and synovial fluid (SF) by ELISA technique. Results: IL-32 staining was detectable in 86.4% of the RA patients, in both the lining and sub lining of the knee synovial tissue. IL-32 expression in the lining highly correlated with microscopic inflammation scores, levels of S TNF-α, levels of S and SF IL-18 (p 0.0001) and also with the acute- phase reaction as measured by the erythrocyte sedimentation rate and C-reactive protein. Both TNF-α and IL-18 were higher in RA patients than in controls. Conclusion: Our results show that the expression of IL-32 is associated with local inflammation in the synovial tissue of patients with RA, and it correlates with both the inflamma-tory cytokines and acute-phase response. These data indicate that IL-32 is a proinflammatory cytokine in RA.