An immune system’s “memory” T cells keep track of the viruses they have seen before, giving the cells a head start in recognizing and fighting off repeat invaders, according to researchers at La Jolla Institute for Immunology (LJI).
Now, a new study led by scientists at LJI, shows that memory helper T cells that recognize common cold coronaviruses also recognize matching sites on SARS-CoV-2, the virus that causes COVID-19. The research was published August 4, 2020, in Science, and may explain why some people have milder COVID-19 cases than others—though the researchers emphasize that this is speculation and much more data is needed.
The new work builds on a recent Cell paper, which showed that 40 to 60 percent of people never exposed to SARS-CoV-2 had T cells that reacted to the virus. Their immune systems recognized fragments of the virus it had never seen before. This finding turned out to be a global phenomenon and was reported in people from the Netherlands, Germany, the United Kingdom and Singapore. Scientists wondered if these T cells came from people who had previously been exposed to common cold coronaviruses. If so, was exposure to these cold viruses leading to immune memory against SARS-CoV-2?
For the new study, the researchers relied on a set of samples collected from study participants who had never been exposed to SARS-CoV-2. They defined the exact sites of the virus that are responsible for the cross-reactive T cell response. Their analysis showed that unexposed individuals can produce a range of memory T cells that are equally reactive against SARS-CoV-2 and four types of common cold coronaviruses.
This discovery suggests that fighting off a common cold coronavirus can indeed teach the T cell compartment to recognize some parts of SARS-CoV-2 and provides evidence for the hypothesis that common cold viruses can, in fact, induce cross-reactive T cell memory against SARS-CoV-2.
