Neutrophils trap bacteria in DNA-rich webs.


Neutrophils spill out their DNA to ensnare and kill extracellular bacteria, according to Volker Brinkmann, Arturo Zychlinsky (Max Planck, Berlin, Germany), and colleagues.

The team figured that degradative enzymes from neutrophils, if they were to be effective, should somehow be directed to meet bacteria. When they looked at elastase localization, they discovered what they call neutrophil extracellular traps (NETs). The fibrous NETs contained degradative enzymes that could destroy bacterial virulence factors, but the overall structures break down with DNase not proteases.

NET formation does not appear to be part of an apoptotic program, and cells with NETs are still alive: they do not release cytoplasmic proteins and continue to exclude vital dyes. (Neutrophils are, however, programmed to die within hours after entering the circulation.) Whether the cells with NETs can later phagocytose bacteria remains unclear.

NETs were apparently seen before by others, but their importance was not realized. Part of their antibacterial action derives from their histones. The antibacterial action of histones was noted back in 1958 by James Hirsch. He was reportedly discouraged by others who questioned the relevance of the result, based on the idea that bacteria would never see histones anyway.

Zychlinksy is now focusing on how NETs are formed, and whether they are directed at bacteria or erected as barriers in which motile bacteria will eventually be snared. ▪


Brinkmann, V., et al.