CITF-funded researchers Drs. Götz Ehrhardt and Mario Ostrowski from the University of Toronto set out to determine whether their pediatric tissue samples from 2015-16 contained signs of immunity to SARS-CoV-2. They discovered immune cells and antibodies in the tonsils that could specifically recognize the virus’ spike protein. The study provides some helpful insights as to why children are better adept at clearing SARS-CoV-2 infection.

Key findings:

  • Pre-existing SARS-CoV-2 reactive B cells were found in pediatric tissue from tonsils dating back to 2015-16.
  • Antibodies secreted from these B cells could identify SARS-CoV-2 and to a lesser extent, SARS, and SARS-CoV-2 variants, but not seasonal coronaviruses.
  • Pre-existing SARS-CoV-2 antibodies have the potential to neutralize the virus.

The researchers extracted B cells, a type of immune cell that secretes antibodies, from cryopreservedCryopreservation is a freezing method that ensures long-term storage of biological material. tonsillar tissue samples from children who had their tonsils removed between 2015 and 2016. Through a series of laboratory experiments, these B cells were introduced to the spike (S) protein of the SARS-CoV-2 virus and were found to recognize it. When isolating the antibodies that these B cells secrete, they found that they too, are responsive to the S protein. Some of these pre-existing SARS-CoV-2 reactive antibodies were also able to recognize the coronavirus that caused the SARS outbreak in 2002-3 (SARS-CoV-1), though none were able to recognize other circulating (and less pathogenic) coronaviruses. Furthermore, the antibodies could only faintly recognize the SARS-CoV-2 variants of concern Alpha and Beta.

What do these findings mean? In short, that the immune system works. The SARS-CoV-2 reactive antibodies in Dr. Ehrhardt’s study were also found to bind to communities of bacteria that naturally reside in our bodies (commensal microbiota). Interestingly, these pre-existing antibodies likely arose in response to a different pathogen and acquired the ability to recognize SARS-CoV-2 as a by-product of the response to the initial immune challenge. These pre-existing antibodies were therefore likely to have other jobs and do not necessarily mean that they have encountered SARS-CoV-2 before. Further, the presence of these SARS-CoV-2 responsive B cells and antibodies in pediatric tissue samples predating the pandemic may also help to explain why children are more adept at clearing SARS-CoV-2 infection without developing severe disease. These observations may constitute the object of future studies.

Yanling Liu, Patrick Budylowski, Shilan Dong, Zhijie Li, Sofiya Goroshko, Leslie Y. T. Leung, Eyal Grunebaum, Paolo Campisi, Evan J. Propst, Nikolas E. Wolter, James M. Rini, Amin Zia, Mario Ostrowski and Götz R. A. Ehrhardt.

SARS-CoV-2–Reactive Mucosal B Cells in the Upper Respiratory Tract of Uninfected Individuals. J Immunol October 4, 2021, ji2100606; DOI: https://doi.org/10.4049/jimmunol.2100606