The common cold is the world’s most widespread infectious disease. Many viruses can cause the symptoms associated with a cold, ranging from a sore throat, blocked nose to a cough. But the virus most commonly associated with the common cold is rhinovirus, which is the leading cause of the common cold, asthma attacks and other respiratory illnesses. You may have also noticed that some people are majorly affected by common cold symptoms while others are only mildly affected by them. Researchers from Yale University set out to discover why this occurs.
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The researchers used epithelial cells from healthy human donors, cultured from either their nasal passages or the lungs. They exposed both cell types, maintained under the same conditions in cell culture, to rhinovirus. The researchers observed a more predominant antiviral response in nasal cells. The researchers then triggered the virus surveillance pathway — known as the RIG-I pathway — in both nasal and lung cells. They found that both cell types generated an antiviral response and a protective response against oxidative stress — a form of cell damage prompted by viruses and other inhaled irritants such as cigarette smoke or tree pollen. The researchers found that the antiviral response was stronger in nasal passages, but defence against oxidative stress was more pronounced in bronchial cells.
Additional experiments revealed that the defence response against oxidative stress shut off antiviral defences. To understand this further, the scientists exposed nasal cells to oxidative stress in the form of cigarette smoke, and then to the cold virus, and found that the nasal cells were more susceptible to the virus. This showed that the nasal cells survived the cigarette smoke but couldn’t fight the virus as well and as a result, the virus gets better.
This finding suggests that there is a delicate balance between the body’s different defence mechanisms. Your airway lining protects against viruses but also other harmful substances that enter airways. When the cold virus enters the nose, cells that line the airways — known as epithelial cells — respond and often clear the virus before it can replicate and trigger symptoms. But when there are two different stressors, there is a trade-off according to the researchers, and the cells try to deal with the other kind of stressor at the cost of the rhinovirus infection.
The study also highlights a link between environmental exposure and the susceptibility to the common cold. The cells in the airway do very well when they are dealing with only one kind of stressor at a time, explaining why smokers are often more susceptible to the common cold.
Source: Cell Reports
