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Mihaela Gadjeva, Qiang Shan; Is immunity a function for chromatin?. Invest. Ophthalmol. Vis. Sci. 2014;55(13):852.
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© ARVO (1962-2015); The Authors (2016-present)
Neutrophil Extracellular Traps (NETs) are a novel, neutrophil-mediated, innate immune response to close-proximity extracellular pathogens. Here, we investigate the molecular composition of NETs released in response to P. aeruginosa infection and the relevance of NETosis for the pathogenesis of ocular keratitis.
Primary human neutrophils were exposed to invasive or cytotoxic P. aeruginosa clinical isolates. The released NET-DNA was quantified, NET fragments were purified, and their protein composition was characterized using LC/MS mass spectroscopy. The antimicrobial activity of the recombinant or purified NET proteins was evaluated. The in vivo presence of NETs was examined in a mouse keratitis model.
The invasive and the cytotoxic P. aeruginosa strains induced NET release. NETs shared a common protein signature regardless of the inducing stimuli. NETs were decorated with histones, elastase, lysozyme, myeloperoxidase, anti-microbial peptides, and proteins of the glycolytic cascade. The molecular make-up of NETs demonstrated the presence of a conserved core of NET-associated proteins suggestive of a potential mechanism for anti-bacterial protection based on metabolic starvation. The P. aeruginosa strains PAO1 (serogroup O5), 6294 (serogroup O6), 6354 (serogroup O8) were sensitive to NET capture, while the 6077 and 6206 strains (serogroup O11) and PA14 (serogroup 010) were resistant. NET binding and killing of P. aeruginosa was dependent on histones H3, but not H2B, H4, or enolase. The histone H3 binding to P. aeruginosa strains was selective and depended on the structure of the LPS O-side chain since the PAO1 strain that was engineered to express the serogroup O11 LPS was resistant to the antimicrobial activity of H3 similar to the clinical isolates 6206 and 6077.
NETs restrict pathogen spread by trapping and metabolically starving bacteria. P. aeruginosa are captured by NET histones depending on the structure of the LPS O-side chain. However NETs might contribute to the pathogenesis of disease when infection is triggered by strains that escape NET capture.
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