Running a fever, feeling tired, and lethargic are just some of the many symptoms of the Common Cold, a viral disease caused by the Rhinoviruses. For decades scientists believed that these symptoms caused by such diseases were due to the activation and working of the immune system alone. It was believed that the immune system would produce inflammatory molecules that would travel via the bloodstream to the brain. However, a new study from researchers at the University of Calgary revealed that this mechanism is much more convoluted than what we thought to be before. Researchers have found that the lungs communicate directly with the brain when there is an infection, thus symptoms associated with diseases (sickness) are a result of nervous system activation in the lungs.
“The lungs are using the same sensors and neurons in the pain pathway to let the brain know there’s an infection,” says Dr. Bryan Yipp, MD '05, MSc'05, clinician-researcher at the Cumming School of Medicine and senior author on the study. “The brain prompts the symptoms associated with sickness; that overall feeling of being unwell, feeling tired, and losing your appetite. The discovery indicates we may have to treat the nervous system as well as the infection.”
Researchers stress that it is imperative to understand the brain-lung dialogue to understand the mechanisms of many diseases, especially bacterial ones. Bacteria produce a biofilm around themselves to prevent detection by the brain. This is the reason that many lung diseases are largely asymptomatic as the brain is unable to detect these particles and produce appropriate symptomatic responses. This was best illustrated during COVID as Yipp explained, “We would have patients whose oxygen levels were extremely low and X-rays confirmed they may need to be put on life support. Yet, when I went to see the patient, they would say I feel fine… These people were experiencing limited sickness symptoms even though the virus was aggressively damaging their lungs.”
What does this mean for future diagnostics and treatment of pulmonary diseases? Firstly, it alters our understanding of respiratory diseases and chronic pulmonary disorders. Before the study, we believed that only the immune system was responsible for the production of symptoms. However, via this study, we understand that symptoms could be a result of nervous system activation in the lungs. Since the study shows that the lungs alter the brain via complex neuronal circuits, and the brain follows suit by producing responses in various organs, new treatment options become conceivable. It means that doctors can target not only the immune system via antibiotics to tackle infection and their symptoms, but also think of targeting neuronal circuits to help alleviate symptoms.
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