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Why Flu Triggers Asthma Attacks in Children


When children with asthma get the flu, the result is often a frightening one, as many kids end up in the hospital. Now researchers have identified a reason why flu can trigger asthma attacks, and the answer may lead to new treatments.

Asthma triggered by flu isn’t well controlled

Asthma is a growing and serious problem among children. The Centers for Disease Control and Prevention reports that about 10 percent of children had asthma in 2009. Among non-Hispanic black children, the rate of asthma is 17 percent. In most asthmatic children, allergies are a major factor.

Viral infections like the flu are also common among children, and when combined with asthma the result can be hospitalization. Thus the new findings of a research team led by Dale Umetsu, MD, PhD, of Children’s Division of Immunology at Children’s Hospital Boston, are of particular interest.

In it, scientists discovered a previously unrecognized biological pathway that explains why flu triggers asthma attacks. Using a mouse model, they found that influenza triggers immune cells called natural helper cells.

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Natural helper cells have only recently been found in the intestinal tract and to play a role in the immune system. According to Umetsu, “since the lung is related to the gut—both are exposed to the environment—we asked if natural helper cells might also be in the lung and be important in asthma.”

Now, Umetsu’s team has found natural helper cells in the lung in a mouse model of flu-induced asthma, but not in allergic asthma. Specifically, they showed that influenza A prompts production of IL-33, a compound that activates natural helper cells, which in turn secrete compounds that trigger asthma.

This discovery may now lead to new ways to treat flu-induced asthma attacks. Umetsu explained that if they can find a way to block activation of natural helper cells or their secretions, it may be possible to better protect children with asthma when they get the flu.

Current treatment of asthma mostly includes drugs that act on immune cells called TH2 cells, which are involved in allergic asthma. In 2006, Umetsu’s team also identified another group of cells, called natural killer T-cells, that also have a role in asthma. Drugs to address natural killer T-cells are still under development.

The discovery of the role of natural helper cells in asthma provides an explanation for why flu causes asthma attacks in children. Umetsu noted that all the identified pathways can be present at one time, and so “we need to understand the specific asthma pathways present in each individuals with asthma and when they are triggered, so we can give the right treatment at the right time.”

Chang Y-J et al. Nature Immunology 2011 May; doi: 10.1038/ni.2045
Centers for Disease Control and Prevention