The neutrophil-recruiting chemokine GCP-2/CXCL6 is expressed in cystic fibrosis airways and retains its functional properties after binding to extracellular DNA

Mucosal Immunol. 2016 Jan;9(1):112-23. doi: 10.1038/mi.2015.43. Epub 2015 May 20.

Abstract

Infections in cystic fibrosis (CF), often involving Pseudomonas aeruginosa, result from a dysregulated airway immunity where one hallmark is the accumulation of necrotic and apoptotic immune cells, in particular neutrophils. In addition, neutrophils actively release DNA, forming neutrophil extracellular traps (NETs) that contain antimicrobial proteins. Altogether, free DNA in complex with actin accumulates in the airway lumen, resulting in highly viscous sputum that provides an anionic matrix, binding cationic antimicrobial proteins. In this study, granulocyte chemotactic protein 2 (GCP-2)/CXCL6, a neutrophil-activating chemokine with bactericidal properties, was detected in the airway epithelium of CF patients and was also present in azurophilic and specific granules of neutrophils. Elastase of neutrophils, but not of P. aeruginosa, completely degraded CXCL6 (chemokine (C-X-C motif) ligand 6). In addition, CXCL6 colocalized with extracellular DNA in both CF sputa and in in vitro-formed NETs. In vitro, CXCL6 bound DNA with a KD of 2,500 nM. Interestingly, both the bactericidal and the receptor-activating properties of CXCL6 (against neutrophils) remained largely unaffected in the presence of DNA. However, the chemotactic properties of CXCL6 were reduced by the presence of DNA. Taken together, CXCL6 is expressed in CF, retaining its functional properties even after binding to the anionic scaffold that extracellular DNA provides in CF.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / immunology
  • Bacterial Proteins / metabolism
  • Case-Control Studies
  • Cystic Fibrosis / enzymology
  • Cystic Fibrosis / genetics
  • Cystic Fibrosis / immunology*
  • Cystic Fibrosis / pathology
  • DNA / immunology*
  • DNA / metabolism
  • Extracellular Traps / chemistry
  • Extracellular Traps / immunology*
  • Gene Expression
  • Humans
  • Leukocyte Elastase / genetics
  • Leukocyte Elastase / immunology*
  • Leukocyte Elastase / metabolism
  • Neutrophil Activation
  • Neutrophil Infiltration
  • Neutrophils / enzymology
  • Neutrophils / immunology*
  • Neutrophils / pathology
  • Protein Binding
  • Proteolysis
  • Pseudomonas aeruginosa / enzymology
  • Respiratory System / enzymology
  • Respiratory System / immunology*
  • Respiratory System / pathology
  • Species Specificity
  • Sputum / chemistry
  • Sputum / immunology

Substances

  • Bacterial Proteins
  • DNA
  • Leukocyte Elastase