Lung infections have been known to cause problems with what is called alveolar fluid clearance, but the effects of the flu on the lungs had not been tested before, Davis said. The alveoli are air spaces deep inside the lungs where oxygen enters the blood in exchange for carbon dioxide to be exhaled.
The scientists used an unusual method to observe the fluid clearance. After being infected, the mice were anesthetized and put on ventilators. The researchers then placed fluid containing protein into one lung of each mouse and tested the fluid 30 minutes later. The amount of protein left in the remaining fluid allowed the investigators to determine whether the infected lung was clearing fluid adequately.
Davis said the study showed that when the flu virus infects cells in the lung, those cells release small molecules, or nucleotides, that are part of the energy-producing and replication machinery of the cell. Those nucleotides then bind to receptors of other cells in a series of events that ultimately shut down the transport of sodium from airways to the blood. All of these interactions take place in the epithelium, the lining of the airways in the lungs.
Under normal conditions, sodium is absorbed from the lungs into the blood and carried away to be excreted by the kidneys. But in infected lungs, when the sodium channels are damaged, more and more fluid builds up in air spaces instead of being pumped across the airway lining and into the blood.
"A little bit of fluid gives us a way to flush the nasties out of the lung," Davis said. "If you get a bacterial infection and bacteria are all over the lungs and cell surfaces, you release these nucleotides and generate fluid so you can cough up the bacteria and wash them out. The downside is as you build up fluid in the lung, you can't oxygenate as well.
|Contact: Ian Davis|
Ohio State University