Fig. 2: Impacts of the gut microbiota on vaccine efficacy.
From: Modulation of oral vaccine efficacy by the gut microbiota
A Acting directly with the vaccine. Many vaccines consist of essential carbohydrates, such as polysaccharide vaccines or targeting ligands, which are polysaccharide structures, so they are easily degraded when exposed to the intestinal environment. B Carrying vaccine-like epitopes induces cross-immunity. The gut microbiota-encoded epitopes increase the ability of B cells or T cells to cross-present antigens and change vaccine-induced immune responses. C Providing immune adjuvants. The gut microbiota provides numerous immune adjuvants that improve vaccine potency. LPS, polysaccharide A, flagellin, and peptidoglycan can activate TLR4, TLR2, TLR5 and NOD2 signaling to modulate immunity. D Immunomodulatory microbiota-derived metabolites. Gut microbial metabolites, such as SCFAs and bile acid, can enhance B-cell metabolism and plasma cell function. SCFAs mediate the inhibition of DC and macrophage maturation, impacting the ability to capture antigens and reducing the production of proinflammatory cytokines. SCFAs can also directly affect the ability of naïve T cells to differentiate into Th1 and Th17 cells. BCR, B-cell receptor; TCR, T-cell receptor; LPS, lipopolysaccharide; TLR, toll-like receptor; APC, antigen-presenting cell; NOD, nucleotide-binding oligomerization domain-containing protein; SCFA, short-chain fatty acid; GPR, G protein-coupled receptor; SIgA, secretory immunoglobulin A. (Created with Adobe illustrator).
