One of the human body's main defences against viral infections may be helping the novel coronavirus infect more cells, according to a study which can help understand why some people are more susceptible than others to COVID-19.
The study, published in the journal Cell, used single-cell RNA sequencing, which identifies which of roughly 20,000 genes are "on" in individual cells, and found that only a tiny percentage of human respiratory and intestinal cells make the proteins that help the virus gain entry into human cells.
"We started to look at cells from tissues such as the lining of the nasal cavity, the lungs, and gut, based on reported symptoms and where the virus has been detected," said Jose Ordovas-Montanes, study co-author from Boston Children's Hospital in the US. "We wanted to provide the best information possible across our entire spectrum of research models," Ordovas-Montanes said.
Recent studies had pointed out that the novel coronavirus, SARS-CoV-2, like the closely related SARS-CoV behind the 2002-03 SARS pandemic, uses a receptor called ACE2 to gain entry into human cells, aided by an enzyme called TMPRSS2. In the current research, the scientists found that only a small fraction of cells, often well below 10 percent, make both ACE2 and TMPRSS2.
They said these cells fall in three categories -- goblet cells in the nose that secrete mucus, lung cells known as type II pneumocytes which help maintain the alveoli sacs where oxygen is taken in, and one type of so-called enterocytes that line the small intestine and aid in nutrient absorption. "Many existing respiratory cell lines may not contain the full mix of cell types, and may miss the types that are relevant," Ordovas-Montanes said.