SAN DIEGO -- Your chances of getting COVID-19 could depend in part on how your body reacted the last time you caught a cold, according to a study published this week by researchers at the La Jolla Institute for Immunology.
SARS-CoV-2, the virus that causes COVID-19, may be the latest coronavirus, but it's not the first. There are four other coronaviruses, which can cause the common cold. The new study shows that some people who have never been infected with SARS-CoV-2 have immune responses to it because they have been exposed to what are essentially older cousins of the novel coronavirus.
Scientists are still figuring out exactly what this all means. But it's possible that people with immune responses to the common coronaviruses may be less likely to get COVID-19, says Alessandro Sette, one of the study's senior authors.
"This may give you a head start," Sette said. "If you have a head start, you may mount a faster response or a stronger response. You might not get as sick."
Sette and colleagues published their findings Tuesday in the journal Science, but their discovery started with a puzzling observation months ago. That was when Sette's team detected immune responses to the novel coronavirus in blood samples collected before the COVID-19 pandemic -- meaning there was no way these samples came from people who had been exposed to the virus.
That finding has since been confirmed by studies of people from the U.S., U.K., the Netherlands, Germany and Singapore. Those reports showed that between one-fifth and half of those who have never been exposed to the novel coronavirus may have an immune response to it.
But why? Sette's team suspected that the four common coronaviruses were the answer. Perhaps some people's immune systems had already seen pieces of the common coronaviruses that were nearly identical to the novel virus.
To put this theory to the test, researchers analyzed blood collected from San Diegans before the pandemic. They found all the areas of the coronavirus targeted by their immune systems and looked for regions of the four common coronaviruses that were nearly identical.
When the scientists used these matching viral regions to stimulate the cells of uninfected people, their immune cells revved up, suggesting that some of these cells could respond both to the previous coronaviruses and to the novel virus.
The findings, based on studying cells in a dish, don't prove that exposure to previous coronaviruses protects against COVID-19. But if so, that would help explain why COVID-19 is deadly for some while others recover with hardly any symptoms (age and preexisting conditions are clearly still important factors too).