A new study has suggested that quitting smoking might reduce the risk of a severe coronavirus infection, as cigarette smoke spurs the lungs to make more of the receptor protein which the virus uses to enter human cells.
The findings were published in the journal Developmental Cell, and may explain why smokers appear to be particularly vulnerable to severe COVID-19 disease.
Study senior author Jason Sheltzer, a cancer geneticist at Cold Spring Harbor Laboratory in the US, said, “We found that smoking caused a significant increase in the expression of ACE2, the protein that SARS-CoV-2 uses to enter human cells.”
According to the scientists, quitting smoking might reduce the risk of a severe coronavirus infection. They said most individuals infected with the virus suffer only mild illness, if they experience any at all.
However, some require intensive care when the sometimes-fatal virus attacks, the researchers said.
In particular, three groups have been significantly more likely than others to develop severe illness — men, the elderly, and smokers.
Turning to previously published data for possible explanations for these disparities, the scientists assessed if vulnerable groups share some key features related to the human proteins that the coronavirus relies on for infection.
First, they focussed on comparing gene activity in the lungs across different ages, between the sexes, and between smokers and nonsmokers.
The scientists said both mice that had been exposed to smoke in a laboratory, and humans who were current smokers had significant upregulation of ACE2.
Smokers produced 30-55 per cent more ACE2 than their non-smoking counterparts.
While the researchers found no evidence that age or sex impacts ACE2 levels in the lungs, they said the influence of smoke exposure was surprisingly strong.
According to the data, the level of the receptors ACE2 in the lungs of people who had quit smoking was similar to that of non-smokers.
The study noted that the most prolific producers of ACE2 in the airways are mucus-producing cells called goblet cells.
Smoking is known to increase the prevalence of such cells.