Two therapies used to control and prevent asthma attacks and allergies might also protect people from a potentially deadly respiratory infection known as influenza viral pneumonia, a new study shows.
The study, “Alveolar Macrophages Prevent Lethal Influenza Pneumonia by Inhibiting Infection of Type-1 Alveolar Epithelial Cells,” appeared in the journal PLos Pathogens.
Influenza viral pneumonia is caused by the direct infection of alveolar epithelial cells, which leads to extensive alveolar inflammation and injury, and is deadly to as many as 40 percent of the people who contract it.
“If infection is severe enough, and the immune response is potent enough, you get injury to these cells and are no longer able to get sufficient oxygen exchange,” Thomas J. Braciale, MD, PhD, of the University of Virginia School of Medicine said in a news release. “As a result of the infection of the cells, you can develop lethal pneumonia and die.”
“The excitement of this is the possibility of someone coming to see the physician with influenza that looks a little more severe than usual and treating them with the drugs Singulair or Accolate and preventing them from getting severe pneumonia,” Braciale said. “The fatality rate from influenza pneumonia can be pretty high, even with all modern techniques to support these patients. So it’s a very serious problem when it occurs.”
Unlike bacterial pneumonia, influenza pneumonia is caused by the Influenza A virus and is very difficult to treat.
“When we look at pandemic strains of influenza that have high mortality rates, one of the best adaptations of those pandemic viruses is their ability to infect these alveolar epithelial cells,” said Amber Cardani, PhD, the study’s first author. “It’s one of the hallmarks for certain strains that cause the lethality in these pandemics.”
Once the influenza virus reaches deep into the lungs, the body’s own immune response can prove harmful, leading to severe damage to the alveoli, the tiny sacs within the lungs that allow for the exchange of oxygen and carbon dioxide.
“It’s an important observation the field is coming to,” Cardani said. “We really need to limit the infection of these lower respiratory airways.”
Alveolar macrophages — white blood cells found in the pulmonary alveolus — are the ideal localized cells to offer a first line of defense against alveolar-invading pathogens such as Influenza A.
In the study, researchers explored the role of alveolar macrophages in regulating the severity of influenza infection in mice models. They found that these macrophages typically protect alveolar epithelial cells (cells lining the alveoli of the lungs) from influenza infection.
But in some cases, the influenza virus can prevent the macrophages from carrying out their protective function, stripping epithelial cells of their defenses.
“It’s not as though they lack alveolar macrophages, it’s just that their alveolar macrophages don’t work right when they get exposed to the flu,” Braciale said. “And those are the types of patients who potentially would eventually go to the intensive care unit, that we think could be treated early in infection with Accolate or Singulair to prevent infection of these epithelial cells and prevent lethal infection.”
Researchers are now investigating if patients being treated with Accolate and Singulair are less prone to developing influenza pneumonia during flu outbreaks.
“This was a totally unexpected observation,” Braciale said. “When I told multiple colleagues who are infectious disease or pulmonary physicians, they were absolutely flabbergasted.”