IL18 and infection: Furthermore, IDO is highly regulated by superoxides and inflammatory mediators, where its expression is increased by IFN-γ[102,103,104,105], tumor necrosis factor-alpha (TNFα) [105,106], tumour growth factor-beta (TGF-β) [96], interleukins 1-beta, 2, 12, 18 (IL1β, IL2, IL12, and IL18) [96], and prostaglandins (PGE2) [105,107,108], as well as pathogenic infections including parasites, viruses, and bacteria.