Lung Microbiome: Bacterial and Human Cells Speaking the Same Language

Researchers at the University of Michigan studying the microbiome of the lungs have found a potential explanation for the recent onset of bacterial lung infections, according to a study published in the American Journal of Respiratory and Critical Care Medicine.

The study explored a "feedback loop" that is experienced when the body's cells form molecules as distress signals in response to stressful situations. These molecules, called catecholamines, or "stress molecules," are the body's primary response to injuries or stress (like adrenaline) and this "feedback loop" is the result of accelerated growth of certain bacteria within these stress molecules.

"Our findings suggest that the human and bacterial cells in our lungs are speaking the same language," Robert Dickson, M.D., an assistant professor of internal medicine, said in a news release. "Our lung's immune cells respond to infection by making catecholamines. Our findings suggest that these catecholamines can in turn make certain dangerous bacteria grow faster, which causes more inflammation and stress signaling. It's a vicious cycle."

The U-M team study took samples from 40 lung transplant patients in different states of health, and discovered that the communities of bacteria in the lungs had collapsed when respiratory infections were present, and that the collapse was associated with the catecholamine levels in the lungs.

Dickson stated that the overall understanding of the microbiome of the lungs is still clouded, and is often overshadowed by the studying of the digestive tract's microbiome. It was previously believed, and still taught, that the lungs were free of bacteria except during infections. In their research published in PLoS Pathogens, Dickson and his partner Gary Huffnagle, Ph.D., have shown that the "ecosystem" of microbes in the lungs may be less extensive than the gut, but is thriving.

"The lungs have their own anatomy, their own physiology, and their own ecology. The rules from the gut microbiome may not apply. We need to start thinking about how pneumonia and other lung diseases emerge from the complex ecosystem of our respiratory tract," Dickson said.

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