Why do some people infected with COVID-19 seem to get by with minor symptoms, while others become critically ill? A new collaborative study led by researchers at Boston Children’s Hospital suggests that the severity of COVID-19 symptoms may be linked to how cells in the nose and throat respond to the virus.
“Many studies looking for risk predictors have looked for signatures in the blood, but blood may not really be the right place to look,” said study co-author José Ordovás-Montañés.
For the current investigation, the experts looked at nasal swabs from 35 adults infected with COVID-19, whose symptoms ranged from mild to severe. Each swab yielded about 562 epithelial cells, and the researchers diligently sequenced the RNA of each and every one.
The researchers found that these cells changed dramatically post-exposure, with mucus-secreting goblet cells increasing in number while mature ciliated cells dwindled. This is notable because the function of mature ciliated cells is to move microbes and debris out of the respiratory organs. Multiple kinds of cells were infected – including goblet cells, immature ciliated cells, and epidermal cells.
The cells sampled from people who exhibited critical symptoms displayed delayed interferon response. Interferons are somewhat like the alarm bell for the immune system, and if they don’t signal to the cells that they’re in danger, the whole immune system may be sluggish to counteract viral infection.
According to Ordovás-Montañés, having the right amount of interferon at the right time could be at the crux of dealing with SARS-CoV-2 and other viruses.
Why and how COVID-19 causes this delayed antiviral signal in the nasopharynx is still unclear. Early evidence suggests that the new COVID variants work in a similar manner. It will be up to future studies to untangle the source of COVID-19’s dangerous inner-workings.
However, the new study does provide some hope. Perhaps if symptoms are recognized early on, interferons could be activated with a nasal spray or drops. “The question is, ‘How do you make these cells more responsive?’” said Ordovás-Montañés.
The study is published in the journal Cell.