Table 3.

Main postbiotic classes and their biological activities (adapted form 254).

Metabolite	Activities	Reference
Butyrate, acetate, propionate	Preserve mucosal immunity Enhance the regulatory function of Tregs in the large intestine Butyrate suppresses proliferation by acting as a HDAC inhibitor Enhance the protection against infections Activate GPR43 and GPR109a on intestinal epithelial cells, result in the activation of the NLRP3 inflammasome leading to production of IL-18. NF-kB inactivation and suppression of pro-inflammatory cytokines and nitric oxide in neutrophils and mononuclear cells through HDAC inhibition	[154,155,156,157,158,159,160,161,162,163,164,165,166,167,168]
Niacin	Induces anti-inflammatory properties in dendritic cells and macrophages in a GPR109a-dependent manner and suppresses colonic inflammation	[160]
Retinoic acid	Dendritic cell induction of gut-lymphocytes Supports the development of Tregs through TGF-β and suppresses the development of TH17 cells during inflammation, RA is required for the induction of a proinflammatory CD4+ helper T cell response	[169,170,171,172]
Polysaccharide A (PSA)	Suppresses the production of pro-inflammatory IL-17 and promotes expression of IL-10 by CD4+ T cells	[156,173,174]
Bile acids	Regulation of bacterial growth Inhibit the induction of pro-inflammatory genes through NF-kB	[175,176,177]
Taurine	Nlrp6 inflammasome activation and contribution to intestinal homeostasis	[178]
Indoles	Induce IL-22 secretion by ILCs, further driving the secretion of antimicrobial peptides and protection from infections by pathogens Epithelial barrier enhancement	[56,179,180]