Lipoteichoic Acid Induces Unique Inflammatory Responses when Compared to Other Toll-Like Receptor 2 Ligands

Departments of Oncology, Biochemistry and Molecular Biology and the Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Canada.
PLoS ONE (Impact Factor: 3.23). 02/2009; 4(5):e5601. DOI: 10.1371/journal.pone.0005601
Source: PubMed


Toll-like receptors (TLRs) recognize evolutionarily-conserved molecular patterns originating from invading microbes. In this study, we were interested in determining if microbial ligands, which use distinct TLR2-containing receptor complexes, represent unique signals to the cell and can thereby stimulate unique cellular responses. Using the TLR2 ligands, R-FSL1, S-FSL1, Pam2CSK4, Pam3CSK4, and lipoteichoic acid (LTA), we demonstrate that these ligands activate NF-kappaB and MAP Kinase pathways with ligand-specific differential kinetics in murine macrophages. Most strikingly, LTA stimulation of these pathways was substantially delayed when compared with the other TLR2 ligands. These kinetics differences were associated with a delay in the LTA-induced expression of a subset of genes as compared with another TLR2 ligand, R-FSL1. However, this did not translate to overall differences in gene expression patterns four hours following stimulation with different TLR2 ligands. We extended this study to evaluate the in vivo responses to distinct TLR2 ligands using a murine model of acute inflammation, which employs intravital microscopy to monitor leukocyte recruitment into the cremaster muscle. We found that, although R-FSL1, S-FSL1, Pam2CSK4, and Pam3CSK4 were all able to stimulate robust leukocyte recruitment in vivo, LTA remained functionally inert in this in vivo model. Therefore distinct TLR2 ligands elicit unique cellular responses, as evidenced by differences in the kinetic profiles of signaling and gene expression responses in vitro, as well as the physiologically relevant differences in the in vivo responses to these ligands.

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    • "For example both lipopolysaccharide and Pam2CSK4 at 100 ng/ml (as used in the present study) induced activation of MAP kinase and NF-B signalling pathways and inflammatory cytokine expression in the murine macrophage/ monocyte cell line Raw 264.7, and bone marrow-derived macrophages from C57BL/6 mice (Long et al., 2009). Importantly, the effects of Pam2CSK4 were TLR2 specific as Pam2CSK4 was unable to induce activation of the above signalling pathways in macrophages from Tlr2 À / À mice (Long et al., 2009). However, assessment of a more extensive dose range of the agonists used in the study should be the focus of future experiments to compliment these studies. "
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    • "IκBα was partially degraded by 15 minutes and remained at low levels throughout the 8-hour time period, except for a brief return to pre-stimulation levels at the 1 hour time point. To our knowledge, such a prolonged absence of cytoplasmic IκBα has not been observed after stimulation with any other TLR2 ligand, including the triacylated lipopeptide, Pam3CSK4 (TLR1/TLR2) or the diacylated lipopeptides, Pam2CSK4 (TLR2/TLR6), S-FSL-1 (TLR2/TLR6) and R-FSL1 (TLR2/TLR6/CD-36) [44]. Hb activation also resulted in IκBα levels that were lower than pre-stimulatory levels at some time points. "
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