As well as carrying genetic instructions, it turns out DNA makes a handy weapon too. 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�
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Normally, immune cells called neutrophils kill microbes by gobbling them up or releasing toxic chemicals. But when all else fails, they disgorge complex nets of their DNA, studded with antimicrobial compounds.
The nets can span small blood vessels, ensnaring and killing . 鈥淲hen bacteria are flowing through the blood, there鈥檚 no chance that a neutrophil could catch them,鈥� says Paul Kubes of the University of Calgary in Canada. 鈥淏ut these nets can entangle them.鈥�
Fungus wars
This defence mechanism was only recently discovered, and now Sheppard鈥檚 team has shown that neutrophils use this kamikaze tactic against Aspergillus fungal infections in the lungs. The fungus, which usually infects people with weakened lungs or immune systems, is a stationary target but 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, though: 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 .
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(Image credit: SPL)
