Expression and function of toll-like receptor 8 and Tollip in colonic epithelial cells from patients with inflammatory bowel disease.
OBJECTIVE
Growing evidence indicates that innate immunity, including toll-like receptor (TLR) signalling, plays a role in inflammatory bowel disease (IBD). This may also apply in the case of TLR-8, which has recently been shown to reverse the immunosuppressive function of regulatory T cells. However, the role of TLR-8 in IBD is currently unknown, and therefore we investigated the expression of TLR-8 and its natural antagonist, Tollip, in normal and inflamed human gut, and examined whether the receptor is functionally active.


METHODS
TLR-8 and Tollip mRNA expression were measured in colonic epithelial cells (CEC) and lamina propria mononuclear cells (LPMNC) by quantitative polymerase chain reaction. TLR-8 protein expression was visualized in whole biopsy specimens by indirect immunofluorescence microscopy. Cellular localization of TLR-8 protein was assessed by immuno-electron microscopy. IL-8 secretion was measured by ELISA after stimulation with TLR-8 ligand.


RESULTS
TLR-8 mRNA and protein expression were substantially up-regulated in CEC from inflamed mucosa from patients with ulcerative colitis (approximately 350-fold, p<0.01) and Crohn's disease (approximately 45-fold, p<0.05) compared to controls. TLR-8 proteins resided on the luminal surface membrane and in intracellular organelles. Tollip was not increased in CEC from IBD patients. CEC from normal mucosa responded to TLR-8 stimulation by secreting IL-8. TLR-8 was expressed only on the mRNA level in LPMNC with no differences between IBD patients and controls.


CONCLUSIONS
Expression of TLR-8, but not Tollip, is highly up-regulated in the colonic epithelium from patients with active IBD. Since the receptor is functionally active, our data suggest that TLR-8 signalling is important in the pathogenesis of IBD.
Steenholdt
Casper
C
Department of Gastroenterology, Herlev Hospital, University of Copenhagen, Denmark.
Andresen
Lars
L
Pedersen
Gitte
G
Hansen
Alastair
A
Brynskov
Jørn
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D003093:Colitis, Ulcerative / Q000235:genetics / Q000503:physiopathology; D003424:Crohn Disease / Q000235:genetics / Q000503:physiopathology; D004847:Epithelial Cells; D005260:Female; D015870:Gene Expression; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000235:genetics* / Q000503:physiopathology*; D016209:Interleukin-8 / Q000097:blood; D007413:Intestinal Mucosa; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D051200:Toll-Like Receptor 8 / Q000096:biosynthesis*; D015854:Up-Regulation
D016209:Interleukin-8; D047908:Intracellular Signaling Peptides and Proteins; C495349:TLR8 protein, human; C410602:TOLLIP protein, human; D051200:Toll-Like Receptor 8