A new study confirms the principle of cross-immunity that previous infections with cold viruses have trained the immune system to recognize SARS-CoV-2.
- Some people who have never been exposed to SARS-CoV-2 have T lymphocytes, white blood cells that are responsible for cellular immunity, which can curb the epidemic.
- This explains why some develop a severe form of the infection while others only have a mild form.
The question of immunity around Covid-19 continues to be the subject of much research. A study published on August 4 in the journal Science by researchers at the La Jolla Institute of Immunology in California (USA) reveals that past exposure to colds has allowed many people to develop an immune system capable of recognizing Covid-19. “This could help explain why some people with Covid-19 have few symptoms while others become seriously ill”, estimates Daniela Weiskopf, co-author of the study.
A good immune memory
Some people who have never been exposed to SARS-CoV-2 have T lymphocytes, white blood cells that are responsible for cellular immunity, which can curb the epidemic. “We have proven that, in some people, pre-existing T-cell memory for common colds can recognize SARS-CoV-2, down to the exact molecular structures”, notes Daniela Weiskopf.
This theory of cross-immunity has already been studied previously and German researchers have shown that immune cells, developed after a simple cold, activate on contact with the coronavirus. This immune response would be long-lasting, compared to the antibodies which are developed by the body after a first infection with Covid-19 and which do not seem to last over time.
T cells, the key
This immune memory could explain why some people develop severe Covid-19 infections when others have milder forms. It is possible that this “immune reactivity results in different degrees of protection against Covid-19said study co-lead author Alessandro Sette. Further research is needed to confirm this. Having a strong T-cell response, or a better T-cell response can give you the opportunity to have a much faster and stronger response.” The exact role of T cells against Covid-19 needs to be clarified.
In this study, researchers analyzed blood samples taken from people between 2015 and 2018. In these samples, T cells reacted at more than 100 specific sites on SARS-CoV-2. The researchers showed that these T cells also react at similar sites on four different coronaviruses that cause cold infections.”This study provides very strong direct molecular evidence that T cells can see sequences that are very similar between common cold coronaviruses and SARS-CoV-2”, added Alessandro Sette.
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