A new discovery could lead to treatments that "turn off" inflammation in the lungs caused by influenza and other infections, according to a new study.
The symptoms of influenza, such as breathlessness, weight loss and fever, can last for many days after the virus has been cleared from the body because the immune system continues to fight the damaged lung.
While the immune system is essential for clearing the virus, it can damage the body when it overreacts if it is not quickly contained. Such overreaction also occurs in a number of other diseases, including asthma and inflammatory conditions in the gut.
During influenza infection, the immune system's prolonged response causes the lungs to become inflamed and this can clog the airways and cause difficulty breathing.
The new study, led by researchers from Imperial College London and published in the journal Nature Immunology, reveals how the activity of immune cells in the lung is normally kept under control by a receptor known as CD200R, working with another molecule called CD200.
CD200R is found in high levels in the lungs and the new research shows that it is able to limit the immune system's response and to turn off inflammation once it has started.
Influenza overrides the CD200 molecule and, without CD200 to bind to, CD200R cannot work to prevent the immune system from overreacting, so the lungs become inflamed.
The researchers found that mice infected with influenza and given an antibody to stimulate CD200R had less inflammation in their airways and lung tissue.
The influenza virus was still cleared from the lungs within seven days, so this strategy did not appear to affect the immune system's ability to fight the virus itself.
Following these results in mice, the researchers hope that a therapy could be developed for people that can stop the immune system from fighting when it is no longer needed.
They believe this would quickly reduce symptoms and reduce the damage that the immune system causes in the lungs and elsewhere.
Professor Tracy Hussell, the lead author of the research from the National Heart and Lung Institute at Imperial College London, said: "Our new research is still in its early stages, but these findings suggest that it could be possible to prevent the immune system going into overdrive, and limit the unnecessary damage this can cause."
Dr Robert Snelgrove, a Sir Henry Wellcome Postdoctoral Fellow at Imperial College London and another author of the research, added: "Although flu is just an inconvenience for some people, it can be dangerous and even fatal in the very young and elderly. We hope our research could ultimately help to develop treatments that fight the effects of this sometimes lethal virus."
The researchers hope that in the event of a flu pandemic, the new treatment would add to the current arsenal of anti-viral medications and vaccines. An advantage of this therapy is that it would be effective even if the flu virus mutated, because it targets the body's overreaction to the virus rather than the virus itself.
In addition to the possible applications for treating influenza, the researchers also hope their findings could lead to new treatments for other conditions where excessive immunity can be a problem, including other infectious diseases, autoimmune diseases and allergy.
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