Primary pathologic role of interleukin-6 in rheumatoid arthritis

BACKGROUND: Interleukin-6 (IL-6) is a polyfunctional cytokine that regulates a very large number of cellular activities. Its implication in acute-phase reactant production by hepatocytes is of particular interest, as is its involvement in chronic inflammatory diseases, mainly rheumatoid arthritis, Crohn's disease, and Castleman's disease. Transgenic mice lacking IL-6 expression were completely protected against collagen-induced arthritis, and Tumor Necrosis Factor (TNF-alpha) induces synovial cells to produce IL-6 and their proliferation. However, there is still some controversies regarding the unique proinflammatory activity of IL-6. Some studies have demonstrated that IL-6 and TNF-alpha may have an opposite effect in synovial cultured cells since IL-6 could represent a negative loop for TNF-alpha induced synovitis. However, phase III studies of rheumatoid arthritis patients treated with anti IL-6 receptor (tocilizumab) indicate an acceptable safety profile relative to the clinical benefit. AIM OF THE STUDY: In this review, we summarized the rationale and the main evidence regarding the therapeutic benefit of blocking IL-6 activity in rheumatoid arthritis. © 2008 Elsevier Srl.