Scientists find immunological clue that may explain severe H1N1 illness

One of the scariest aspects of the H1N1 pandemic is the apparent randomness of the virus: While most people who contract it recover from symptoms after several days, pockets of people are hit with extremely severe, and sometimes deadly, illness.

One of the scariest aspects of the H1N1 pandemic is the apparent randomness of the virus: While most people who contract it recover from symptoms after several days, pockets of people are hit with extremely severe, and sometimes deadly, illness.

Now, it appears scientists are one step closer to understanding why some people may be at greater risk of developing virulent forms of H1N1, as well as other respiratory illnesses.

Toronto scientists, in collaboration with colleagues from Spain, have identified a molecule they believe is linked to severe forms of illness. The results, published in the December issue of the journal Critical Care, could eventually help health officials target populations that may be most vulnerable, they said.

“It’s probably not an isolated example that is specific for H1N1, and it probably spills over to other types of respiratory illness,” said David Kelvin, senior scientist and head of the experimental therapeutics division at the Toronto General Research Institute and one of the study’s authors.

The researchers looked at blood samples from 10 H1N1-infected individuals in intensive-care units, 10 patients in non-ICU parts of the hospital, 15 outpatients with the illness and 15 people without H1N1. They focused on analyzing 29 cytokines, or molecules that regulate immune function, to determine if there were any patterns among those with severe forms of the disease.

They discovered that those patients with the most virulent forms had elevated levels of one particular molecule called interleukin 17. High levels of the molecule have previously been associated with inflammation and autoimmune diseases, Kelvin said.

It’s too early to draw a link between high levels of that molecule and the risk of pneumonia or death related to H1N1, he said.

It is still not known if elevated levels of the molecule can predict severe illness, or whether it applies to large groups of people. But the finding does give scientists a solid basis to work with as they continue in their quest to identify what makes certain people more vulnerable to virulent respiratory illness.

Kelvin said he and his colleagues have been searching for this kind of discovery for years, and they believe it has implications for targeting preventive therapy in future pandemics, as well as seasonal influenza. While they have looked in the past at patients with other respiratory illnesses, they never found a meaningful connection between severe illness and elevated molecule levels.

“This is the first time we’ve come across something in 10 years, and we’ve looked pretty rigorously,” he said. “It’s almost like a smoking gun. If you don’t know where to look, you’ll never get the job done.”

Kelvin said researchers are expanding their study to look for similar patterns in people living in other countries, such as China. They hope to find links between molecule levels and severe illness, and will look for genetic differences that may make some people more susceptible to severe illness.

Eventually, health officials may be able to develop a simple blood test that can identify who is at greatest risk of severe illness in future pandemics or flu outbreaks.

Kelvin said the work could have major implications for developing countries, which often can’t afford comprehensive inoculation campaigns to protect their populations.

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