TNF and rheumatoid arthritis: In PsA, levels of interleukin (IL)-1β, IL-6, IL-17, IL-22, IL-23, interferon-γ, and tumour necrosis factor-α (TNF-α) are elevated, while in RA, levels of IL-1, IL-6, IL-17, IL-22, IL-33, and TNF-α are elevated [7,8].