fig7

Figure 7. Immunomodulatory mechanisms of gut microbiota-derived tryptophan metabolites, structural components (PSA), and 5-HT. The schematic depicts the production of key bacterial derivatives in the gut lumen (left) and their subsequent signaling axes within the liver tumor microenvironment (right), primarily focusing on the AhR, TLR2, and 5-HT pathways. Solid arrows indicate promotion, activation, or metabolic conversion; blunt-ended lines indicate inhibition or receptor antagonism; dashed arrows indicate translocation from the gut to the liver. Detailed cellular interactions and clinical implications for ICI response are comprehensively discussed in the corresponding text. PSA: Polysaccharide A; AhR: aryl hydrocarbon receptor; TLR2: Toll-like receptor 2; 5-HT: 5-hydroxytryptamine; IDO1: indoleamine 2,3-dioxygenase 1; HCC: hepatocellular carcinoma; Treg: regulatory T cell; DC: dendritic cell; TIM-3: T-cell immunoglobulin and mucin-domain containing-3; PD-1i: programmed cell death protein 1 inhibitor.