title: Human intestinal microvascular endothelial cells express Toll-like receptor 5: a binding partner for bacterial flagellin.
abstract: Bacterial flagellin has recently been identified as a ligand for Toll-like receptor 5 (TLR5). Human sites known to specifically express TLR5 include macrophages and gastric and intestinal epithelium. Because infection of intestinal epithelial cells with Salmonella leads to an active transport of flagellin to the subepithelial compartment in proximity to microvessels, we hypothesized that human intestinal endothelial cells functionally express TLR5, thus enabling an active inflammatory response upon binding of translocated flagellin. Endothelial expression of TLR5 in human macro- and microvascular endothelial cells was examined by RT-PCR, immunoblot analysis, and immunofluorescence. Endothelial expression of TLR5 in vivo was verified by immunohistochemistry. Endothelial modulation of ICAM-1 expression was quantitated using flow cytometry, and leukocyte transmigration in vitro was assessed by an endothelial transmigration assay. Epithelial-endothelial cellular interactions upon infection with viable Salmonella were investigated using a coculture system in vitro. We found that Salmonella-infected intestinal epithelial cells induce endothelial ICAM-1 expression in cocultured human endothelial cells. Both macro- (HUVEC) and microvascular endothelial cells derived from human skin (human dermal microvascular endothelial cell 1) and human colon (human intestinal microvascular endothelial cells) were found to express high constitutive amounts of TLR5 mRNA and protein. These findings were paralleled by strong immunoreactivity for TLR5 of normal human colonic microvessels in vivo. Furthermore, incubation of human dermal microvascular endothelial cells with flagellin from clinical isolates of Escherichia and Salmonella strains led to a marked up-regulation of ICAM-1, as well as to an enhanced leukocyte transendothelial cell migration. These results suggest that endothelially expressed TLR5 might play a previously unrecognized role in the innate immune response toward bacterial Ags.
authors.affiliation: Department of Medicine B, University of Muenster, Muenster, Germany. maaser@uni-muenster.de
authors.forename: Christian
authors.initials: C
authors.lastname: Maaser
authors.forename: Jan
authors.initials: J
authors.lastname: Heidemann
authors.forename: Christof
authors.initials: C
authors.lastname: von Eiff
authors.forename: Andreas
authors.initials: A
authors.lastname: Lugering
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Spahn
authors.forename: David G
authors.initials: DG
authors.lastname: Binion
authors.forename: Wolfram
authors.initials: W
authors.lastname: Domschke
authors.forename: Norbert
authors.initials: N
authors.lastname: Lugering
authors.forename: Torsten
authors.initials: T
authors.lastname: Kucharzik
mesh_terms: D018938:Caco-2 Cells; D002465:Cell Movement / Q000276:immunology; D002478:Cells, Cultured; D018920:Coculture Techniques; D003106:Colon / Q000098:blood supply / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D029968:Escherichia coli Proteins / Q000378:metabolism; D005408:Flagellin / Q000378:metabolism*; D019073:HT29 Cells; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000096:biosynthesis; D007413:Intestinal Mucosa / Q000166:cytology / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D007962:Leukocytes / Q000166:cytology / Q000276:immunology; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D008833:Microcirculation / Q000166:cytology / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D011485:Protein Binding / Q000276:immunology; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000378:metabolism; D013347:Subcellular Fractions / Q000276:immunology / Q000382:microbiology; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors; D020298:U937 Cells; D015854:Up-Regulation / Q000276:immunology
chemical_list: D029968:Escherichia coli Proteins; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; C495346:TLR5 protein, human; D051198:Toll-Like Receptor 5; D051193:Toll-Like Receptors; D018799:Intercellular Adhesion Molecule-1; D005408:Flagellin