AS WELL as carrying the instructions for how to build you, it turns out DNA makes a handy weapon. As a last-ditch defence against invading microbes, immune cells spew out sticky nets of their DNA.
鈥淒NA is so physically packed that when you uncoil it you get a huge net,鈥� says of McGill University in Montreal, Canada. 鈥淚t鈥檚 like one of those cans of exploding snakes, only a thousand times more dramatic.鈥�
Normally, immune cells called neutrophils kill microbes by gobbling them up or releasing toxic chemicals. But recently it was found that when all else fails, they disgorge nets of DNA studded with antimicrobial compounds, destroying themselves in the process. The nets can span small blood vessels, ensnaring and killing .
Advertisement
Now Sheppard鈥檚 team has shown that neutrophils also use this tactic against fungal infections in the lungs (PLoS Pathogens, ). Aspergillus usually infects people with weakened lungs or immune systems, and is too big for a neutrophil to ingest, so the immune cells use their nets to deliver a concentrated dose of toxins.
But one virulent strain of Aspergillus seems to evade destruction. Work in mice suggests that this strain has acquired a sugary coating that repels the nets, so Sheppard鈥檚 team is .
The neutrophil nets have a downside, however: they may trap any cancerous cells circulating in the bloodstream, helping them spread into nearby tissues and seeding the growth of secondary tumours.
鈥淚t鈥檚 a double-edged sword,鈥� says , also at McGill University. He has shown that when mice with a version of lung cancer are given drugs that dissolve the nets, they develop .
This article appeared in print under the headline 鈥淪elf-sacrificing immune cells spew DNA net鈥�