During the pandemic, doctors and researchers noticed that children and adolescents infected with COVID-19 got less sick than adults. One of the possible explanations is that the children already had a previous level of immunity to COVID-19 provided by the memory T cells generated by having suffered common colds.
After studying single blood samples from children taken before the pandemic, researchers at the Karolinska Institutet in Sweden, and the universities of Bern (Switzerland), Oslo (Norway) and Linköping University (Sweden) have succeeded in identifying T cells from memory cells that react to cells infected with SARS-CoV-2, the virus that causes COVID-19.
One possible explanation for this immunity in children is that they already had colds caused by one of the four coronaviruses that cause seasonal common cold symptoms. This could stimulate an immune response with T cells capable of also reacting to cells infected with SARS-CoV-2.
This new study reinforces this hypothesis and demonstrates that T cells previously activated by the OC43 virus can cross-react against SARS-CoV-2. “These reactions are especially strong early in life and become much weaker as we get older,” says study author Annika Karlsson, research group leader at the Karolinska Institutet’s Department of Laboratory Medicine. “Our findings show how the T cell response develops and changes over time and may guide future monitoring and vaccine development.”
The results of the work, which has been published in the journal Proceedings of the National Academy of Sciences, indicate that the response of memory T cells to coronaviruses develops from the age of two. The study was based on 48 blood samples from children between the ages of two and six and 94 samples from adults between the ages of 26 and 83. The analysis also included blood samples from 58 people who had recently recovered from COVID-19.
“Next, we would like to do analogous studies of young and older children, adolescents, and young adults to better track how the immune response to coronaviruses develops from childhood to adulthood,” says Marion Humbert, a postdoctoral researcher, currently at the Huddinge Department of Medicine.
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