Flu Research Finds Harmful Immune Response

Researchers have infected mice with a replica of the deadly 1918 flu virus. As expected, all the mice died within days. But not because the virus directly destroyed the lungs. Instead, it triggered an overwhelming and self-destructive immune response. That fits with emerging research on one way viruses kill.

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Researchers want to prepare for the next flu pandemic by studying the past. They've been examining the flu outbreak that killed millions starting in 1918, and they say they're beginning to understand why it was so deadly.

NPR's Richard Knox reports.

RICHARD KNOX: The most striking feature of the 1918 flu is that it killed healthy young adults in days. Flu expert Michael Katze of the University of Washington.

Prof. MICHAEL KATZE (Flu Expert, University of Washington): People were bleeding from their mouth. Their lungs were completely destroyed. I mean it was an extremely quick and dramatic death, very unlike most influenza virus symptoms.

KNOX: The original 1918 virus doesn't exist anymore. But recently scientists pieced together the virus' eight genes from fragments in victims' lung tissue. And in a viral version of Jurassic Park, they used the genes to build a living replica of the monster.

In this week's edition of Nature, they describe what happened when they infected mice with the replica.

Prof. KATZE: What this paper shows us is that there is a very dramatic response in the lungs of infected mice. In my view, the fate of the mouse is sealed minutes, certainly hours, after infection.

KNOX: What's important is how the virus inflicts such sudden and overwhelming damage. It's not because it directly attacks lung tissue, it's because the virus triggers a self-destructive reaction by the immune system.

Katze says no single gene from the flu virus is responsible for this immune storm.

Prof. KATZE: These viral genes, or these viral proteins, are talking to each other. They're coordinating with each other.

KNOX: In one sense, that may be reassuring. If it takes most or all eight genes to be this lethal, that might reduce the chances that the current bird flu virus could swap one or two genes with an ordinary flu virus and thus become a 1918-type threat.

That's more than an academic question. The latest cluster of bird flu cases in Indonesia involves a family in which one 15-year-old girl had ordinary flu, while her brother had the deadly chicken flu. Scientists urgently need to know whether that sets the stage for a 1918-like catastrophe.

Richard Knox, NPR News.

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