A coronavirus infection can cut down the even cilia forests that cover our airways, destroying a crucial barrier to prevent the virus from lodging at the bottom of the lungs.
Typically, these cilia move in synchronized waves to push mucus from the airways and throat. To protect the lungs, non-belonging objects (including viral invaders such as the coronavirus) are trapped in the mucus, which is then swallowed (SN: 15/09/20).
But the coronavirus throws that system out of itself. When it infects the cells of the respiratory tract, the virus appears to clean the cilia of the cilia, and without the paired structures, the cells stop moving mucus, the researchers reported on July 16 in Nature Communications.
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That lack of cilia could help the virus invade the lungs and cause severe COVID-19, says Lisa Chakrabarti, a viral immunologist at the Pasteur Institute in Paris (SN: 6/11/20). Understanding how coronavirus invades different parts of the body can help researchers find ways to block it.
Chakrabarti and colleagues infected laboratory-cultured human cells that mimic the lining of the respiratory tract with coronavirus. The images showed short, fat cilia on the surface of the infected cells instead of the long projections found in the healthy cells. When the team added microscopic pearls to the surface of the infected cells to measure the movement of mucus, those pearls were largely immobile, a sign that the cells would not move mucus through the airways and throat to be swallowed.
Cilia usually move in synchronized waves to move the mucus away from the lungs, towards the throat where foreign objects are swallowed. But coronavirus-infected cells lose those cilia and no longer push mucus, removing a barrier that would normally help prevent the virus from invading the lungs. Here the microscopic beads move first over the surface of the uninfected laboratory-grown cells and then around the infected cells, illustrating the movement of the mucus. The color lines show how fast the spheres move, blue indicates slower speeds, and red notes faster speeds.
Other viruses and bacteria can also damage the body’s ability to use mucus to trap and eliminate foreign invaders, Chakrabarti says. Some pathogens, such as coronavirus, only damage the cilia and leave intact the cells from which they protrude. Other pathogens, such as the flu, can kill hair cells. Respiratory syncytial virus, which usually causes colds, can do both: in adults, it destroys cilia; in children, it can kill cells, which can be fatal.
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