How the Intricate Interaction among Toll-Like Receptors, Microbiota, and Intestinal Immunity Can Influence Gastrointestinal Pathology

Table 1

Human TLRs: an overview on their pathophysiology.

	Ligand(s)	Cell types	Genetic defect	Association
TLR 1	(i) Triacyl lipopeptides	(i) Monocytes/macrophages; (ii) Dendritic cells; (iii) B lymphocytes	TLR1-R80T	Ulcerative colitis, pancolitis
TLR 2	(i) Glycolipids; (ii) Lipopeptides; (iii) Lipoproteins; (iv) Lipoteichoic acid; (v) HSP-70; (vi) Zymosan; (vii) Others	(i) Monocytes/macrophages; (ii) Neutrophils; (iii) Myeloid dendritic cells; (iv) Mast cells	TLR2-R753Q	Ulcerative colitis, pancolitis
TLR 6	(i) Diacyl lipopeptides	(i) Monocytes/macrophages; (ii) Mast cells; (iii) B lymphocytes	TLR6-S249P	Decreased incidence of proctitis in IBD
TLR 4	(i) Lipopolysaccharide; (ii) Heat shock proteins; (iii) Fibrinogen; (iv) Heparan sulfate; (v) Hyaluronic acid; (vi) Nickel; (vii) Various opioid drugs	(i) Monocytes/macrophages; (ii) Neutrophils; (iii) Myeloid dendritic cells; (iv) Mast cells; (v) B lymphocytes; (vi) Intestinal epithelium	TLR4-D299G	Increased susceptibility to IBD
TLR 5	(i) Flagellin	(i) Monocyte/macrophages; (ii) Dendritic cells; (iii) Intestinal epithelium	TLR5-STOP	Decreased susceptibility to IBD
TLR 9	(i) Unmethylated CpG; (ii) Oligodeoxynucleotide DNA	(i) Monocytes/macrophages; (ii) Plasmacytoid dendritic cells; (iii) B lymphocytes	TLR9-SNPs: −1237T/C −2848A/G	Susceptibility to Crohn’s disease