Table 3. PRR-mediated mechanisms of postbiotics and their applications across food, feed, and clinical fields

Postbiotic component	Host receptor(s) / signaling pathway	Key physiological effects	Application area	References
Peptidoglycan	TLR2, NOD2 → NF-κB, MAPK	Immune modulation, suppression of excessive inflammation	Functional foods, immune-supportive products	Taverniti & Guglielmetti, 2011; Saito et al., 2020
Lipoteichoic acid (LTA)	TLR2 → MyD88–NF-κB	Cytokine regulation, immune homeostasis	Functional foods, dietary supplements	Lebeer et al., 2010; Taverniti & Guglielmetti, 2011
S-layer proteins	TLR2, DC-SIGN → NF-κB	Epithelial barrier protection, pathogen exclusion	Gut health foods, clinical nutrition	Konstantinov et al., 2008; Szabó et al., 2023
Exopolysaccharides (EPS)	TLR2, C-type lectin receptors → MAPK	Antioxidant activity, gut barrier enhancement	Functional foods, metabolic health	Lebeer et al., 2010; Teame et al., 2020
Short-chain fatty acids (SCFAs)	GPR41/43 → AMPK activation, HDAC inhibition	Barrier integrity, anti-inflammatory and metabolic regulation	Functional foods, feed additives	Kang et al., 2021
Microbial DNA (CpG motifs)	TLR9 → IRF/NF-κB	Th1 activation, innate immune stimulation	Clinical and immune-supportive applications	Wischmeyer et al., 2016
Inactivated LAB cells	PRR-mediated mucosal signaling	Reduced pathogen adhesion, gut stability	Animal feed	de Almada et al., 2016
Cell wall fragments	NF-κB, MAPK modulation	Improved gut morphology, reduced inflammation	Livestock feed	Bhattarai et al., 2025
Postbiotic metabolites	SCFA-related signaling pathways	Improved feed efficiency, growth performance	Livestock production	Cui et al., 2025