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. 2021 Jun 18;41(8):661–694. doi: 10.1002/cac2.12182

FIGURE 4.

FIGURE 4

Role of microbial metabolites in cancer immunity. SCFAs, AHR ligands, secondary BAs, polyamines and PSA, the bacterial metabolites, are involved in cancer progression and the efficacy of anticancer therapies by influencing the host immune system. SCFAs inactivate DCs and promote proliferation and immune regulation of Treg cells through GPR41, GPR43 and GPR109A, and inhibit the activity of NF‐κB and the secretion of TNF in peripheral blood mononuclear cells and neutrophils by inhibiting HDAC. AHR ligands serve a function in regulating adaptive immunity through binding to AHR. BAs activate BAR and GPBAR1 to inactivate inflammation. In addition, secondary BAs, the products of primary BAs metabolized by bacteria, reduce hepatic NKT cells. PSA promotes CD4+ T cells to express IL‐10, induces naive CD4+ T cell differentiation toward the Th1 subtype via a DC‐dependent manner, and activates the expression of TLR2 to induce the secretion of IL‐10, thereby inactivating Teff cells. Abbreviations: AHR: aryl hydrocarbon receptor; BAR: bile acids receptor; BAs: bile acids; DC: dendritic cell; GPBAR1: G protein‐coupled BA receptor 1; GPR: G protein‐coupled receptor; HDAC: histone deacetylase; IL: interleukin; NF‐κB: nuclear factor kappa‐B; NKT: natural killer T; PSA: polysaccharide A; Teff: effector T; TLR 2: Toll‐like receptor 2; TNF: tumor necrosis factor; Treg: regulatory T; SCFA: short‐chain fatty acid