Canadian Scientists Explain How Cytokine
Storms Affect Pandemic Flu Severity
Canadian scientists have helped make a discovery that might
explain why some people develop severe illness when infected with
H1N1 flu and others don't.
The researchers from Toronto's University Health Network found
high levels of a molecule called interleukin 17 in the blood of
severely ill H1N1 patients, and low levels in patients with mild
forms of the disease.
Interleukin 17 is a cytokine, a kind of molecule that helps regulate
the body's white blood cells which fight viral, bacterial and
But interleukin 17 can also go "out of control" in
some cases and has been linked with such inflammatory autoimmune
diseases as rheumatoid arthritis and asthma.
In the cases of respiratory infections, cytokines plays a part
in a potentially fatal immune reaction called a "cytokine
storm," in which the immune system of a healthy person goes
haywire and "overreacts" to an infection. The cytokines
command a patient's body to flood the lungs with fluids and mucous,
which can eventually block off the airways and "drown"
Cytokine storms are what are thought to have caused many of the
deaths in the SARS outbreak, bird flu, and the 1918 Spanish flu,
which killed a disproportionate number of otherwise healthy adults.
For this latest study, to be published in the journal Critical
Care, the Toronto researchers joined a team from Spain to examine
a group of otherwise healthy Spanish patients who became infected
with H1N1 during the first wave, in July and August 2009. The
group included 20 hospitalized patients, 15 outpatients with mild
forms of the illness, and 15 control subjects who weren't infected.
The researchers focused on 29 cytokines and analyzsed them to
find any patterns among the study volunteers.
They found that those with severe symptoms from the flu had elevated
levels of interleukin 17, while patients with the mild form of
the disease had low levels.
Dr. David Kelvin, the leader of the Canadian team and the head
of the Experimental Therapeutics Division at the Toronto General
Hospital Research Institute, says the discovery is the first clue
about what could be causing some patients to develop potentially
fatal lung inflammation and pneumonia.
Kelvin said it is still not known whether high levels of interleukin
17 are always present in patients, or if they are overproduced
only in response to the virus. But he told the Globe and Mail
that IL-17 levels are likely high in patients who develop other
"It's probably not an isolated example that is specific
for H1N1, and it probably spills over to other types of respiratory
illness," he said.
Kelvin said his team believes the discovery could lead to preventive
therapies that would target IL-17 in future flu pandemics and
other outbreaks, potentially speeding recovery.
As well, a test to determine who has high levels of the molecule
could be possible in the near future.
"A diagnostic test could let us know early who is at risk
for the severe form of this illness quickly," he said, noting
that high levels would indicate a failure of the immune system
to eliminate the virus.
He cautioned, though, that the clinical application of this work
is still many years away.
Researchers are now expanding on the study to look for similar
patterns in people living in other countries, such as China.
Reference Source: ctv.ca
December 17, 2009