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Volume 14 Supplement 2

Sepsis 2010

Soluble TLT-1 is a naturally occurring TREM-1 inhibitor and protects mice from hyperresponsiveness and death during sepsis

Introduction

Triggering receptor expressed on myeloid cells-1 (TREM-1) and TREM-like transcript 1 (TLT-1) belong to the TREM family. TREM-1 is expressed on neutrophils and monocytes/macrophages, and plays a crucial role during the onset of sepsis by cooperating with pattern recognition receptors in a synergistic way, thus amplifying the host immune response. TLT-1 is selectively expressed on activated platelets and is known to facilitate platelet aggregation through binding to fibrinogen. Interestingly, TLT-1 null mice displayed higher plasma cytokines concentrations and death rates than WT mice during experimental sepsis. We identified a 17 amino acid peptide derived from the extracellular part of TLT-1, named LR17, which is responsible for TLT-1 anti-inflammatory properties.

Methods

To quantify cellular activation, human neutrophils were isolated from whole blood by density gradient. After stimulation with LPS, αTREM-1 (a TREM-1 agonist) and/or LR17, p38-MAPK and ERK1/2 phosphorylation was quantified by western blot; NF-κB activity and cytokine release by ELISA; mRNA levels of various gene of interest by quantitative RT-PCR; and ROS production by flow cytometry. The effect of siRNA-induced Trem-1 silencing was studied on purified human monocytes. In vivo studies were performed on a CLP mouse model of sepsis.

Results

αTREM-1-induced or LPS-induced cytokine/chemokine production by human neutrophils or monocytes was dose-dependently reduced in the presence of recombinant TLT-1 or LR17, both at the gene (mRNA) and protein levels (ELISA). This decrease involves a broad set of cytokines and chemokines: TNFα, IL-1β, IL-6, IL-8, IL-16, GRO-α, MCP-1, MIP-1β, and RANTES. Exploration of intracellular signalling showed that LR17 also reduced αTREM-1-induced or LPS-induced p38-MAPK and ERK1/2 phosphorylation, NF-κB activation and then ROS production in neutrophils (Figure 1a to e). On Trem-1-silenced monocytes, TREM-1 agonist did not induce cytokine production and LR17 did not show any effect (Figure 1f). As a result of this activity, both early and late LR17 administration to septic mice modulated the proinflammatory cascade triggered by infection with a decrease of plasma, bronchoalveolar lavage and peritoneal fluid cytokine concentration, as well as of cytokine mRNA levels in the lung and liver. TLT-1 also prevented organ damage and coagulation abnormalities and finally improved survival by more than 60% versus controls (Figure 2 overleaf).

Figure 1
figure1

LR17 decreases LPS-associated and αTREM-1-associated human neutrophil activation.

Figure 2
figure2

LR17 protects mice from caecal ligation and puncture (CLP)-induced mortality. (a) Dose-response curves. (b) Delayed LR17 administration.

Conclusions

TLT-1 plays a pivotal role during sepsis, linking haemostasis and inflammation.

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Correspondence to M Derive.

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Derive, M., Bouazza, Y., Massin, F. et al. Soluble TLT-1 is a naturally occurring TREM-1 inhibitor and protects mice from hyperresponsiveness and death during sepsis. Crit Care 14, P43 (2010). https://doi.org/10.1186/cc9146

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Keywords

  • Human Neutrophil
  • Cytokine Concentration
  • Amino Acid Peptide
  • Septic Mouse
  • Trigger Receptor