Lipopolysaccharide and Double-stranded RNA Up-regulate Toll-like Receptor 2 Independently of Myeloid Differentiation Factor 88

Abstract

Toll-like receptor 2 (TLR2) is a signaling receptor for a variety of microbial products, including bacterial lipoproteins and peptidoglycan, and is central in initiating immune responses toward Gram-positive bacteria, spirochetes, and mycobacteria. The mechanisms behind regulation of TLR2 protein expression are still not well understood. By using a newly developed monoclonal antibody against mouse TLR2, we detected TLR2 protein expression on macrophages, neutrophils, and dendritic cells. Endogenous macrophage TLR2 localized mostly to the cell membrane, with particular accumulation around phagosomes containing zymosan. Treatment of macrophages with the TLR2 antibody diminished cellular response to lipoproteins and down-regulated membrane TLR2. Marked up-regulation of surface TLR2 was observed on macrophages in response to whole bacteria, lipoproteins, lipopolysaccharide, poly(I-C) (doublestranded RNA), R848, and CpG DNA, and this up-regulation appeared to be a very sensitive marker for the presence of microbial products. Up-regulation of TLR2 in response to stimuli correlated with an increased response to secondary lipoprotein exposure following a low concentration of primary lipoprotein challenge. By comparison, exposure to a larger primary challenge induced a hyporeactive state. Most interestingly, lipopolysaccharide-and double-stranded RNA-induced upregulation of surface TLR2 in macrophages was found to be MyD88-independent, whereas the up-regulation in response to lipoproteins, R848, and CpG DNA was absent in MyD88-deficient cells. We conclude that complex mechanisms regulate expression and signaling via TLR2. Up-regulation of TLR2 in the presence of low, yet clinically relevant amounts of microbial products may be an important mechanism by which the immune system boosts its response to a beginning infection.

Ligand-induced differential cross-regulation of Toll-like receptors 2, 4 and 5 in intestinal epithelial cells

“…Cross-talk between TLR2 and TLR4 signaling pathways have been reported in murine macrophages and endothelial cells (Fan et al, 2003;Matsuguchi et al, 2000;Nilsen et al, 2004;Totemeyer et al, 2003). Interestingly, the effects in these cell types are in agreement to that what we observed for intestinal mIC cl2 epithelial cells.…”

“…In fact, activation of TLR2 or TLR4 through commensal bacteria turns out to be a prerequisite for the protection against epithelial damage (Rakoff-Nahoum et al, 2004). For macrophages and endothelial cells, cross-talk between TLR2 and TLR4 resulting in alterations in TLR expression and/or function has been demonstrated (Fan et al, 2003;Matsuguchi et al, 2000;Nilsen et al, 2004;Totemeyer et al, 2003). Knowledge of the factors that control TLR expression and function in intestinal epithelial cells is still in its infancy but is crucial to facilitate future targeted modulation or restoration of intestinal homeostasis.…”

Microbial Products Stimulate Human Toll-like Receptor 2 Expression through Histone Modification Surrounding a Proximal NF-κB-binding Site

“…Our results showing induction of the TLR2 gene are consistent with several studies indicating that murine Tlr2 is induced by pro-inflammatory mediators (17,19). However, data from previous studies on the response of the human TLR2 gene have been somewhat inconsistent, with some groups claiming that the gene is inducible by microbial stimuli (5,21) and others reporting no effect (7,22).…”

“…Several groups have begun to characterize the response of the TLR2 gene to various pro-inflammatory stimuli. Murine Tlr2 has been shown to be induced by whole bacteria as well as LPS and inflammatory cytokines (17). In addition, the murine Tlr2 promoter has been analyzed and found to contain binding sites for NF-B and Sp1, both of which are required for transcriptional induction (18 -20).…”

Anakinra and etanercept prevent embryo loss in pregnant nonobese diabetic mice

“…Anakinra and etanercept influence embryo loss microbial products (Nilsen et al 2004). Therefore, there should be a greater focus on the prevention of multiple infections during pregnancy in clinical practice.…”