CCR2 drives neutrophil infiltration and elicits tissue damage in remote organs during sepsis

Introduction

The severe form of sepsis is associated with multiple organ dysfunction syndrome (MODS), but the precise mechanisms by which MODS develops remain unclear. Neutrophils are essential cellular components of the innate immune system that have conserved roles in bacterial containment. Paradoxically, however, neutrophils also mediate tissue injury in varied human diseases, including sepsis.

Objective

In the present study, we investigated the role of chemokine receptor CCR2 in driving neutrophil infiltration and eliciting tissue damage in remote organs during sepsis.

Methods and results

We demonstrated that neutrophils, which are normally unresponsive to CCR2 chemokines, acquired substantial chemotaxis to CCL2 and CCL7 when exposed to LTA (4.33-fold and 3.02-fold increase, respectively) or LPS (4.67-fold and 3.29-fold increase, respectively). Moreover, consistent with the functional response, we found that TLR2 and TLR4 signaling through the MyD88/NF-κB pathway mediates the upregulation of CCR2 and chemotactic responsiveness to CCR2 ligands on neutrophils. In vivo, intravenous injection of TLR ligands or induction of cecal ligation and puncture (CLP)-induced sepsis triggered chemotaxis of circulating neutrophils to CCR2 chemokines, which was completely abolished in MyD88-deficient mice. Notably, CCR2-deficient (CCR2^-/-) or WT mice treated with CCR2 antagonist (RS504393, 2 mg/kg) showed a significant increased survival rate after CLP when compared with WT mice. Deficiency or pharmacology blockade of CCR2 attenuated neutrophil infiltration (by myeloperoxidase activity) into the lungs, heart, and kidneys, which was associated with reduction of serum biochemical markers of organ injury/dysfunction. Importantly, neutrophils from septic patients (n = 19, prospected in survivors (S) and nonsurvivors (NS)) showed an increase of median of fluorescence intensity (MFI) of CCR2 by flow cytometry (S = 5.76 ± 2.30 vs. NS = 9.12 ± 1.72, MFI), which was related to the chemotactic response to CCL2 (S = 6.35 ± 0.68 vs. NS = 10.56 ± 2.38, neutrophils/field). Furthermore, there was a positive correlation between SOFA scores with the neutrophil response to CCL2 (r² = 0.62, P < 0.01).

Conclusions

Collectively, our study identified CCR2 as an important receptor that drives the inappropriate infiltration of neutrophils into remote organs during sepsis. Therefore, CCR2 blockade could be an adjuvant therapeutic strategy for treatment of sepsis-induced MODS.