Table 1.

Functions of microbial products in pathogenesis of IBS.

Microbial Products	Visceral Pain	GI Motility	Mucosal Permeability	Mucosal Inflammation	Influencing Dysbiosis	References
Neurotransmitters
Histamine	↑↑	↑	↑	↑		[53,78,79,80,81,82,83,84]
Serotonin	↑	↑	↑	↑	++	[7,85,86,87,88]
Glutamate	↑↑		↓?	↑	+	[89,90,91,92,93,94,95,96,97,98,99]
γ-aminobutyric acid	↓	↓		↓		[92,100,101,102,103,104,105]
Noradrenalin	↑	↑	↑	↑↓		[106,107,108,109,110,111]
Dopamine	↓	↑↓	↑?	↓?	+	[112,113,114,115,116,117,118]
Acetylcholine		↑		↓		[111,112,119,120]
Compounds
Toll-like receptor ligands	↑↓	↑↓	↑↓	↑↓		[121,122,123]
Cytokines	↑↓	↑↓	↑↓	↑↓		[52,124,125,126,127,128,129,130]
Pore-forming toxins, N-formylated peptides	↑		↑	↑		[124,131,132,133]
Metabolites
Tryptophan (aryl hydrocarbon receptor, kynurenine pathways)	↓↑		↓	↓	+	[89,124,134,135,136,137,138,139,140,141]
Short-chain fatty acids	↑↓	↑	↓	↓		[70,142,143,144,145,146,147,148,149,150,151,152,153,154]
Bile acids	↓	↑		↑	+	[155,156,157,158,159,160]
Vitamin D and B6	↓		↓	↓	+	[161,162,163,164,165,166,167,168,169,170]
Endocrine factors
Glucagon-like peptide-1	↓	↓		↓		[171,172,173,174,175]
Peptide YY	↓	↓				[172,176,177,178]
Enzymes
Proteases	↑	↑↓	↑↑↑	↑		[124,179,180,181,182,183,184,185,186]

↑, up-regulated; ↓, down-regulated; +, positive.