TNF and psoriatic arthritis: Tumor necrosis factor (TNF) is an important human cytokine (Beutler et al., 1985) that is involved in a number of critical biological processes and diseases, including rheumatoid arthritis, Crohn’s disease, multiple sclerosis, inflammatory bowel disease, psoriatic arthritis, AIDS, and cancer (Kollias et al., 1999; Apostolaki et al., 2010).