In a new study, researchers found how smoking cigarettes causes more severe infection by SARS-CoV-2, the virus that causes COVID-19, in the airways of the lungs.
They used a model of airway tissue created from human stem cells.
The finding could help researchers better understand COVID-19 risks for smokers and could inform the development of a new treatment to help reduce smokers’ chances of developing severe disease.
The research was conducted by a team at UCLA.
Cigarette smoking is one of the most common causes of lung diseases, including lung cancer and chronic obstructive pulmonary disease.
Most studies of COVID-19 patients have indicated that current smokers are at increased risk of severe infection and death. But the reasons why have not been entirely clear.
In the study, the team examined what happens when the airways of a current smoker are infected with SARS-CoV-2.
They utilized a platform known as an air-liquid interface culture, which is grown from human airway stem cells and closely replicates how the airways behave and function in humans.
The airways, which carry air breathed in from the nose and mouth to the lungs, are the body’s first line of defense against airborne pathogens like viruses, bacteria and smoke.
The model replicates the upper part of the airways, which is the first place the virus hits.
The air-liquid interface cultures used in the study were grown from airway stem cells taken from the lungs of five young, healthy, nonsmoking tissue donors.
To replicate the effects of smoking, the researchers exposed these airway cultures to cigarette smoke for three minutes per day over four days.
Next, the group infected the cultures exposed to cigarette smoke — along with identical cultures that had not been exposed — with live SARS-CoV-2 virus and the two groups were compared.
In the models exposed to smoke, the researchers saw between two and three times more infected cells.
Digging further, they found that smoking resulted in more severe SARS-CoV-2 infection, at least in part, by blocking the activity of immune system messenger proteins called interferons.
Interferons play a critical role in the body’s early immune response by triggering infected cells to produce proteins to attack the virus, summoning additional support from the immune system, and alerting uninfected cells to prepare to fight the virus.
Cigarette smoke is known to reduce the interferon response in the airways.
The team says if the airways are like the high walls that protect a castle, smoking cigarettes is like creating holes in these walls. Smoking reduces the natural defenses and that allows the virus to set in.
One author of the study is Dr. Brigitte Gomperts.
The study is published in Cell Stem Cell.
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