Alterations in tryptophan metabolism have been shown associated with levels of various anti-inflammatory cytokines, interleukin 6 (IL-6), tumor necrosis factor-alpha (TNFα) and other interferons (IFNs), which is produced in a rapid and transient manner in response to infection or tissue injury, and contributes to host defense by stimulating acute phase responses, haematopoiesis and immune responses [57]. The gene discussed is TNF; the disease is infection.