IL18 and rheumatoid arthritis: Many different pathways contribute to the pathogenesis of RA, especially pro-inflammatory cytokine pathways such as those mediated by tumour-necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), IL-18, IL-6, interferon gamma (IFN-γ), and granulocyte-macrophage colony-stimulating factor (GM-CSF).