Evidence against the microbicidal action of neutrophil extracellular traps (NETs)

Neutrophil extracellular traps (NETs) are fibrillary structures composed of extruded nuclear chromatin decorated with granule proteins (mostly neutrophil elastase, cathepsin G and myeloperoxidase). It has been reported that NETs are able to kill bacteria and fungi based upon the observation that smaller number of organisms are obtained in plating assays after they are incubated with NETs than if the DNA is pre-digested with DNase. It is possible that the microbial killing is apparent rather than real, and occurs because the organisms are aggregated on the DNA structure, and that the plating assay results were simply misinterpreted. The present study shows that digestion of DNA after incubation of NETs with the microbes restores their numbers to preincubation levels indicating that the apparent killing is an artefact of the assay.