Fig. 2

Features of arginine metabolism in M1-type and M2-type macrophages. M1 macrophages are induced by pro-inflammatory cytokines or LPS and are characterized by the expression of iNOS to produce immune response modulator NO and citrulline. M2 macrophages are induced by anti-inflammatory cytokines such as IL-4, IL-10, and IL-13 and express Arg1 to generate L-ornithine and urea, which are precursors of polyamine and proline synthesis. Functionally, M1 macrophages have powerful antitumor activity, while M2 macrophages promote tissue repair, suppress inflammation and promote tumor development. iNOS, inducible nitric oxide synthase; NO, nitric oxide; ROS, reactive oxygen species; NFE2L2, gene coding for the nuclear factor erythroid 2-like 2 (Nrf2); NF-κB, gene coding for the nuclear factor kappa-b subunit; LPS, lipopolysaccharide; IFNγ, interferon γ; IL-4, interleukin-4; IL-10, interleukin-10; IL-13, interleukin-13; Arg I/II, arginase type I/II; TGFβR, transforming growth factor beta receptor