Scientists learning why the flu may kill

PHILADELPHIA, May 5 (UPI) -- Researchers at the Children's Hospital of Philadelphia say they have discovered clues to why influenza is more severe in some victims than others.

The study, published online in the Journal of Leukocyte Biology, shows the influenza virus can paralyze the immune systems of otherwise healthy individuals, leading to severe secondary bacterial infections, such as pneumonia. Furthermore, this immunological paralysis can be long-lived, which is important to know when developing treatment strategies to combat the virus, the study says.

"We have a very limited understanding of why some people who get influenza simply have a bad cold and other people become very sick and even die," senior researcher Dr. Kathleen Sullivan says in a statement.

Sullivan said colleagues recruited pediatric patients with severe influenza and examined the level of cytokines, which serve as the first line initiators of immune response, in the blood plasma.

The researchers found elevated levels of cytokines, but they also found a decreased response of toll-like receptors, which activate immune cell responses as a result of invading microbes. This suggests the diminished response of these receptors may be responsible for the paralysis of the immune system, leading to secondary bacterial infections such as pneumonia, Sullivan says.