Interleukin 6 blockade: tocilizumab in psoriatic arthritis.

Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy of unknown etiology that is associated with psoriasis. Joint destruction is often progressive: almost half of the patients attending an early arthritis clinic showed radiological damage 2 years after diagnosis. Proinflammatory cytokines are major mediators of systemic and local inflammation, and high levels of interleukin 1 (IL-1), IL-6, and tumor necrosis factor have been found in psoriatic skin lesions and the synovial tissue of patients with rheumatoid arthritis and PsA. IL-6 is a pleiotropic cytokine that mainly signals by membrane (neutrophil and lymphocyte) or soluble (endothelial cell) IL-6 receptors. IL-6 was originally identified as a factor in B cell differentiation, but is now known to influence T cell development: in the presence of IL-6 and transforming growth factor-ß (TGF-ß), naive T cells develop into Th17 cells, which are important mediators in PsA. IL-6 may also directly contribute to the epidermal hyperplasia seen in psoriatic epithelium and affect the function of dermal inflammatory cells. However, there are no data concerning the use of tocilizumab in patients with PsA, although a pilot study is currently being carried out because the role of IL-6 in the pathogenesis of PsA supports the idea that targeted treatments against IL-6 might be effective.