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PLoS One. 2014 May 15;9(5):e97784. doi: 10.1371/journal.pone.0097784. eCollection 2014.

New aspects on the structure of neutrophil extracellular traps from chronic obstructive pulmonary disease and in vitro generation.

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Department of Cell Biology, University of Salzburg, Salzburg, Austria.
Department of Pediatrics, Paracelsus Medical University, Salzburg, Austria.
Department of Cell Biology, University of Salzburg, Salzburg, Austria; Clinic of Operative Dentistry, Periodontology and Preventive Dentistry, Saarland University, Homburg, Germany.
University Clinic of Pneumology, Paracelsus Medical University, Salzburg, Austria.


Polymorphonuclear neutrophils have in recent years attracted new attention due to their ability to release neutrophil extracellular traps (NETs). These web-like extracellular structures deriving from nuclear chromatin have been depicted in ambiguous roles between antimicrobial defence and host tissue damage. NETs consist of DNA strands of varying thickness and are decorated with microbicidal and cytotoxic proteins. Their principal structure has in recent years been characterised at molecular and ultrastructural levels but many features that are of direct relevance to cytotoxicity are still incompletely understood. These include the extent of chromatin decondensation during NET formation and the relative amounts and spatial distribution of the microbicidal components within the NET. In the present work, we analyse the structure of NETs found in induced sputum of patients with acutely exacerbated chronic obstructive pulmonary disease (COPD) using confocal laser microscopy and electron microscopy. In vitro induced NETs from human neutrophils serve for purposes of comparison and extended analysis of NET structure. Results demonstrate that COPD sputa are characterised by the pronounced presence of NETs and NETotic neutrophils. We provide new evidence that chromatin decondensation during NETosis is most extensive and generates substantial amounts of double-helix DNA in 'beads-on-a-string' conformation. New information is also presented on the abundance and location of neutrophil elastase (NE) and citrullinated histone H3 (citH3). NE occurs in high densities in nearly all non-fibrous constituents of the NETs while citH3 is much less abundant. We conclude from the results that (i) NETosis is an integral part of COPD pathology; this is relevant to all future research on the etiology and therapy of the disease; and that (ii) release of 'beads-on-a-string' DNA studded with non-citrullinated histones is a common feature of in vivo NETosis; this is of relevance to both the antimicrobial and the cytotoxic effects of NETs.

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