Babies who get severe respiratory viral infections are much more likely to suffer from asthma as they get older. Now a study has identified a key mechanism that when blocked, might help in preventing asthma in kids. The study, led by Mitchell Grayson, M.D., assistant professor of medicine in the Division of Allergy and Immunology at Washington University School of Medicine, has found a key step in the development of asthma in mice after a severe respiratory infection.
The researchers suggest that medications designed to interfere with the mechanism of severe respiratory infection could potentially prevent many cases of childhood asthma. "A severe respiratory infection in infancy greatly increases the risk of developing asthma," Grayson said.
"Less than one in 30 people who don't suffer a severe respiratory infection as a baby develop asthma, but of those who do get these infections, one in five goes on to have asthma," he said. The reasons for the increased trend of asthma in kids were unclear, Grayson indicated. But he suggested that a growing population density and the resulting increase in transmission of respiratory viral infections might be a cause.
Respiratory syncytial virus (RSV) is a common source of respiratory infections. Severe RSV infections can be typified by persistent coughing, wheezing and gasping for breath. In order to investigate the connection between severe respiratory viral infections and subsequent asthma, the researchers used mice genetically selected to have asthma susceptibility and infected them with a virus similar to RSV.
The analysis of the study found that severe respiratory infections in the mice induced an allergic-type immune response and ultimately caused long-term changes in the airways of the lungs that are hallmarks of chronic asthma. The study revealed that certain immune cells in the mouse lungs reacted to severe viral infections by releasing compounds that instigated an inflammatory response that in turn induced many lung airway cells to transform into mucus-producing cells, which can cause the obstruction of lung passages and shortness of breath characteristic of asthma.
The researchers found that by interfering with the process by altering the immune cells or removing the inflammatory compounds they secreted prevented overgrowth of mucus-producing cells. The study found that mice that developed asthma-like symptoms after a severe respiratory viral infection had an unusual immune reaction.
During the infection, the mice produced antibodies and immune signals similar to those produced during an allergic response, instead of those typically made in response to infection, which started a chain reaction that led to asthma. The team proposed that a similar reaction occurs in some people who suffer severe respiratory viral infections.
"We think genetically predisposed individuals will tend to have this kind of immune reaction to a severe respiratory viral infection," Grayson said. "In those people an allergic-type response could be part of their antiviral immune response. That sets them up to make antibodies against a lot of environmental substances, like pet dander or pollen, and they can go on to develop allergies or asthma," he added.
According to Grayson, the findings promise a new approach to asthma prevention, "This offers a different way of thinking about what happens in the development of asthma," Grayson said. "It may be possible to prevent many cases of asthma and other chronic inflammatory airway diseases by stopping allergic-type antibody production after a severe viral infection in infants," he added.
The study is published in the Journal of Experimental Medicine.