By looking for the mechanism that allows influenza A to invade lung cells, scientists also discovered a treatment that might block the virus from taking hold there.
An infection of the lungs is called pneumonia, which is caused by bacteria, viruses, and fungi that target alveoli (air sacs that line the lung). These tiny sacs share a wall with capillaries responsible for moving oxygen molecules into the blood.
Normally, when you breathe, incoming air fills the alveoli, then the alveoli pass oxygen through to the capillaries, which then transfer oxygen into your bloodstream. When you exhale, the alveoli deflate, moving carbon dioxide out of your body. But during a pneumonia infection, the air sacs fill with fluid or pus, reducing your intake of oxygen—and your ability to breathe.
Those most at risk of pneumonia are children under five, adults over 65, and those with compromised immune function from chronic illness. There are vaccinations that lower your risk of contracting pneumonia, and medications that treat the infection when it occurs.
One of the vaccinations that can reduce your odds of getting pneumonia is the influenza vaccination. While influenza usually remains in the upper respiratory tract, when it progresses to the alveoli, it can be serious.
The 1918 outbreak of "Spanish Flu" killed between 20 and 40 million people around the world. Death came quickly as victims appeared to suffocate, sometimes within hours of onset of infection. Later research suggests many, if not most, of those deaths were caused by pneumonia after infection with the influenza virus.
According to the Centers for Disease Control and Prevention (CDC), influenza remains a major threat to human health that is responsible for between 12,000 and 56,000 deaths per year in the US, depending on the severity of the flu season.
In a new study, published in PLOS Pathogens, scientists found two common asthma medications could interrupt the ability of influenza to take hold in alveoli sacs. Once influenza is established, it kills protective cells in the respiratory system, leaving the lungs open to attack by pneumonia.
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. As a result of the infection of the cells, you can develop lethal pneumonia and die.
In this engineered mouse study, researchers analyzed the behavior of immune system microbes called alveolar macrophages. Macrophages are the "big-eaters" of the immune system, a type of white blood cell that attacks and digests foreign pathogens and cellular debris.
Alveolar macrophages that reside in the lungs are first responders to inhaled pathogens. In their study, scientists learned the macrophages not only defend, but also modulate susceptibility of alveoli to influenza. In addition to learning how macrophages preserve alveoli, they learned influenza can disrupt macrophage function, leaving alveoli as open targets to pneumonia infection.
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.
The study also surprisingly revealed that blocking the signaling pathways in alveoli reduced their susceptibility to infection—and antagonism or blocking of those receptors can be done with two existing asthma drugs, Singulair and Accolate.
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. The fatality rate from influenza pneumonia can be pretty high, even with all modern techniques to support these patients. Up to 40 percent. So it's a very serious problem when it occurs.
While influenza cases in the US remain elevated, there was recently some decrease in the number of cases reported. The same does not hold true for reports of influenza pneumonia related deaths. According to the CDC, as of February 23, 2017, 7.8 percent of deaths were due to pneumonia, which is slightly higher than the epidemic threshold of 7.5 percent.
Pneumonia can kill at any age. Up next for the University of Virginia research team is evaluating incidence of influenza pneumonia in patents already using these asthma drugs. "This was a totally unexpected observation," Braciale said. "When I told multiple colleagues who are infectious disease or pulmonary physicians, they were absolutely flabbergasted."