IL4 and brain neoplasm: It is reported that inflammatory cytokines present in brain tumor microenvironment (IFN-α, IFN-γ, TNF-α, TGF-β, IL-4, and IL-23) can activate this altered metabolism through induction of different enzymes involved in different steps of KP such as Indoleamine 2,3-dioxygenase (IDO) which converts tryptophan to kynurenine [156].