Toll-like receptors 2 and 4 are up-regulated during intestinal inflammation.
OBJECTIVE
Bacterial wall products play an important role in the activation of immune and nonimmune cells of the intestinal mucosa. Toll-like receptors (TLRs) TLR2 and TLR4 have been identified as signaling receptors activated by bacterial wall components.


METHODS
Expression of TLRs in human intestinal mucosa obtained by endoscopy and surgery was analyzed by immunohistochemistry. Intestinal macrophages were isolated by immunomagnetic beads armed with a CD33 antibody. Reverse-transcription polymerase chain reaction was performed for TLR1-5. Results were confirmed by Northern blot and flow cytometry. Interleukin-1beta messenger RNA (mRNA) was quantified by a polymerase chain reaction-enzyme-linked immunosorbent assay-kit.


RESULTS
Immunohistochemistry revealed a significant increase in the TLR2 and TLR4 antigen expression on submucosal cells in inflamed intestinal mucosa compared with non-inflamed mucosa. TLR expression was localized in intestinal macrophages by double-labeling techniques. No TLR-polymerase chain reaction product could be obtained with mRNA from CD33-positive macrophages from normal mucosa. We observed an induction of mRNA for TLR2, TLR4, and TLR5 in inflammation-associated macrophages. TLR1 and TLR3 were only detectable in blood monocytes. Monocytes reacted to lipopolysaccharide stimulation with a 3-fold and in vitro differentiated macrophages with a 16-fold increase of cellular interleukin-1beta mRNA. Macrophages from normal mucosa did not respond to lipopolysaccharide showing the functional relevance of TLR expression.


CONCLUSIONS
This study shows the inflammation-dependent induction of TLR2 and TLR4 expression in intestinal macrophages. The absence of TLRs abolishes the reactivity of mucosal macrophages to bacterial wall products. Presence of TLRs may thereby contribute to the inflammatory process.
Hausmann
M
M
Department of Internal Medicine I, University of Regensburg, Regensburg, Germany.
Kiessling
S
S
Mestermann
S
S
Webb
G
G
Spöttl
T
T
Andus
T
T
Schölmerich
J
J
Herfarth
H
H
Ray
K
K
Falk
W
W
Rogler
G
G
D001773:Blood Cells / Q000378:metabolism; D029721:Drosophila Proteins; D004751:Enteritis / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism / Q000473:pathology; D008264:Macrophages / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D012016:Reference Values; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors; D015854:Up-Regulation
D029721:Drosophila Proteins; D007375:Interleukin-1; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; C495344:TLR3 protein, human; C495345:TLR4 protein, human; C495346:TLR5 protein, human; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors