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Cigarette smoke spurs the lungs to produce more of the protein that the coronavirus harnesses to enter human cells, according to new research.

Scientists at Cold Spring Harbor Laboratory (CSHL) in New York found that smoke from cigarettes prompts lungs to produce more ACE2, or angiotensin-converting enzyme 2.

Researchers and clinicians have observed major differences in how people respond to infection. Most suffer only mild illness, if any, while others require emergency-room care. Men, the elderly and smokers have been seen as more likely to develop severe illness, according to researchers.

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Smoking changes the lungs in ways that make the coronavirus more likely to bind to lung cells. (CSHL)

"We started gathering all the data we could find," CSHL Fellow Jason Sheltzer said in a statement, explaining that he and other researchers focused first on comparing gene activity in the lungs across different ages, between the sexes, and between smokers and nonsmokers.

"When we put it all together and started analyzing it, we saw that both mice that had been exposed to smoke in a laboratory and humans who were current smokers had significant upregulation of ACE2," he added.

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Their findings, reported Saturday in the journal Developmental Cell, could explain why smokers appear to be particularly vulnerable to severe infections.

The analysis also indicated that the change is reversible, suggesting that quitting smoking might reduce the risk of severe coronavirus infection.

As of Tuesday evening, the coronavirus had killed at least 91,661 and infected more than 1.5 million people in the U.S.