DNA Is an Antimicrobial Component of Neutrophil Extracellular Traps

Abstract

Neutrophil extracellular traps (NETs) comprise an ejected lattice of chromatin enmeshed with granular and nuclear proteins that are capable of capturing and killing microbial invaders. Although widely employed to combat infection, the antimicrobial mechanism of NETs remains enigmatic. Efforts to elucidate the bactericidal component of NETs have focused on the role of NET-bound proteins including histones, calprotectin and cathepsin G protease; however, exogenous and microbial derived deoxyribonuclease (DNase) remains the most potent inhibitor of NET function. DNA possesses a rapid bactericidal activity due to its ability to sequester surface bound cations, disrupt membrane integrity and lyse bacterial cells. Here we demonstrate that direct contact and the phosphodiester backbone are required for the cation chelating, antimicrobial property of DNA. By treating NETs with excess cations or phosphatase enzyme, the antimicrobial activity of NETs is neutralized, but NET structure, including the localization and function of NET-bound proteins, is maintained. Using intravital microscopy, we visualized NET-like structures in the skin of a mouse during infection with Pseudomonas aeruginosa. Relative to other bacteria, P. aeruginosa is a weak inducer of NETosis and is more resistant to NETs. During NET exposure, we demonstrate that P. aeruginosa responds by inducing the expression of surface modifications to defend against DNA-induced membrane destabilization and NET-mediated killing. Further, we show induction of this bacterial response to NETs is largely due to the bacterial detection of DNA. Therefore, we conclude that the DNA backbone contributes both to the antibacterial nature of NETs and as a signal perceived by microbes to elicit host-resistance strategies.

NETosis Delays Diabetic Wound Healing in Mice and Humans

“…Unlike dsDNA, the NET-associated enzymes elastase and proteinase-3 were higher in patients with infected wounds, especially wounds infected with Gram-positive bacteria. S. aureus DNase helps bacteria to escape the NETs, and extracellular dsDNA provides the majority of the antibacterial activity of NETs (22). Thus, NET enzymes alone would not be able to clear bacteria but would nonetheless damage the tissue (23).…”

Neutrophil extracellular traps — the dark side of neutrophils

“…It is therefore likely that citrullination of histones, which loosen their grip on DNA, make it possible for DNA to interact with bacteria and exert the antibacterial effect of NETs (52). Calprotectin, a member of the S100A family of cytosolic proteins, inhibits growth of fungi by chelating divalent metal in controls (73).…”

Histones as Mediators of Host Defense, Inflammation and Thrombosis

“…The linker histone H1 has also recently been found in NETs where it can form an epitope for autoantibody formation [64]. Of note, a recent study reached somewhat different conclusions through showing that DNA itself plays a key role in the antibacterial activity of NETs through calcium chelation [65].…”