Enteroendocrine cells express functional Toll-like receptors.
Intestinal epithelial cells (IECs) provide a physical and immunological barrier against enteric microbial flora. Toll-like receptors (TLRs), through interactions with conserved microbial patterns, activate inflammatory gene expression in cells of the innate immune system. Previous studies of the expression and function of TLRs in IECs have reported varying results. Therefore, TLR expression was characterized in human and murine intestinal sections, and TLR function was tested in an IEC line. TLR1, TLR2, and TLR4 are coexpressed on a subpopulation of human and murine IECs that reside predominantly in the intestinal crypt and belong to the enteroendocrine lineage. An enteroendocrine cell (EEC) line demonstrated a similar expression pattern of TLRs as primary cells. The murine EEC line STC-1 was activated with specific TLR ligands: LPS or synthetic bacterial lipoprotein. In STC-1 cells stimulated with bacterial ligands, NF-kappaB and MAPK activation was demonstrated. Furthermore, the expression of TNF and macrophage inhibitory protein-2 were induced. Additionally, bacterial ligands induced the expression of the anti-inflammatory gene transforming growth factor-beta. LPS triggered a calcium flux in STC-1 cells, resulting in a rapid increase in CCK secretion. Finally, conditioned media from STC-1 cells inhibited the production of nitric oxide and IL-12 p40 by activated macrophages. In conclusion, human and murine IECs that express TLRs belong to the enteroendocrine lineage. Using a murine EEC model, a broad range of functional effects of TLR activation was demonstrated. This study suggests a potential role for EECs in innate immune responses.
Bogunovic
Milena
M
Div. of Gastroenterology and Hepatology, Univ. of North Carolina School of Medicine, 103 Mason Farm Rd., Campus Box 7032, 7341C MBRB, Chapel Hill, NC 27599-7032, USA.
Davé
Shaival H
SH
Tilstra
Jeremy S
JS
Chang
Diane T W
DT
Harpaz
Noam
N
Xiong
Huabao
H
Mayer
Lloyd F
LF
Plevy
Scott E
SE
D000818:Animals; D018938:Caco-2 Cells; D002118:Calcium / Q000378:metabolism; D054426:Chemokine CXCL2; D018925:Chemokines / Q000378:metabolism; D002766:Cholecystokinin / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019858:Enteroendocrine Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007113:Immunity, Innate; D053762:Interleukin-12 Subunit p40 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051194:Toll-Like Receptor 1 / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D051193:Toll-Like Receptors / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D054426:Chemokine CXCL2; D018925:Chemokines; D017077:Culture Media, Conditioned; C404915:Cxcl2 protein, mouse; D053762:Interleukin-12 Subunit p40; D008070:Lipopolysaccharides; D016328:NF-kappa B; C495342:TLR2 protein, human; C495345:TLR4 protein, human; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D012701:Serotonin; D002766:Cholecystokinin; D020929:Mitogen-Activated Protein Kinase Kinases; D002118:Calcium