TNF and psoriasis: In the early years, studies showed that pro‐inflammatory cytokines, including tumor necrosis factor, interferon‐γ, interleukin‐6, interleukin‐8, interleukin‐12, interleukin‐18,21 and unspecific inflammation markers, for example, C‐reactive protein and haptoglobin,22 increased in serum of psoriasis patients.