Bacterial DNA Activates Endothelial Cells and Promotes Neutrophil Adherence through TLR9 Signaling

Abstract

TLR9 detects bacterial DNA (CpG DNA) and elicits both innate and adoptive immunity. Recent evidence indicates that TLR9 is expressed in more diverse cell types than initially thought. In this study, we report that HUVECs constitutively express TLR9 and selectively recognize unmethylated CpG motifs in bacterial DNA and synthetic immune stimulatory CpG oligodeoxynucleotides. HUVECs respond to CpG DNA with rapid phosphorylation of IκB-α and NF-κB-mediated gene transcription and surface expression of the adhesion molecules ICAM-1 and E-selectin independent of MAPK signaling. The telomere-derived TLR9 inhibitory oligonucleotide 5′-TTT AGG GTT AGG GTT AGG G-3′, agents that block endosomal acidification such as chloroquine and bafilomycin A, and NF-κB inhibitors abrogated CpG DNA-induced signaling. HUVEC activation by CpG DNA led to markedly enhanced neutrophil adhesion under nonstatic conditions that was further enhanced when neutrophils were stimulated with CpG DNA. The adhesive interactions were blocked by Abs against CD18 and, to a lesser degree, by anti-E-selectin and anti-L-selectin Abs. Our findings demonstrate that bacterial DNA promotes β2 integrin and E-selectin-mediated HUVEC-neutrophil adherence, and indicate the ability of CpG DNA to initiate and/or maintain the inflammatory response.

Recombinant Thrombomodulin Inhibits Lipopolysaccharide-Induced Inflammatory Response by Blocking the Functions of CD14

“…Recent studies reported that CD14 is involved in the activation of TLR2, TLR3, TLR7, and TLR9, because CD14-null mice and CD14-deficient cells display less inflammatory response to the specific ligands of these TLRs (5-7). We also observed that addition of rCD14 to endothelial cells, which do not express the membrane form of CD14 but do express TLR4 and TLR9 (8,30,31), markedly increased IL-6 secretion by HUVECs after LPS or CpG-ODN challenge. rTMD23 not only inhibited LPS-induced IL-6 secretion by HUVECs, it also suppressed CpG-ODN-induced IL-6 production, suggesting that the anti-inflammatory capability of rTMD23 occurs through specific suppression of CD14 functioning.…”

TLR9 Bone Marrow Chimeric Mice Define a Role for Cerebral TNF in Neuroprotection Induced by CpG Preconditioning

“…CpG is known to activate endothelial cells leading to increased expression of adhesion molecules (e-selectin, p-selectin, ICAM, VCAM) and chemokines (IL-8 and MCP-1). 7 Additionally, activated endothelial cells are known to secrete and transport TNF. 22 LPS-stimulated brain endothelial cells in vitro have been shown to secrete TNF in a polarized manner preferentially releasing TNF on the luminal side and into the peripheral circulation.…”

“…TLR9 is expressed on a wide variety of cell types both in the brain (microglia, neurons, astrocytes, cerebral vascular endothelium) and on hematopoietic cells in the periphery. [7][8][9][10][11] Thus, it is unknown whether CpG preconditioning activates TLR9 on cells within the brain or whether TLR9 signaling in systemic circulating cells is required to elicit the neuroprotective phenotype.…”

“…7 Hematopoietic cell activation can induce changes in parenchymal tissues including the brain, resulting in a secondary cascade of events. 15 In addition, it is possible that CpG administered systemically crosses the blood-brain barrier (BBB) to directly affect the brain.…”

The role of pattern recognition receptors in the innate recognition ofCandida albicans

“…89,90 Human umbilical vein endothelial cells (HUVECs) express TLR3 and TLR9. [91][92][93] Human dermal microvascular endothelial cells express MR. 94 Besides, Galection-3 was detected on cultured endothelial cells. 95 The expression of Dectin-1 on endothelial cells is controversial.…”