A German research team publishes in the journal Nature a study demonstrating a possible cross-reactivity between the SARS-CoV-2 virus and certain other coronaviruses responsible for the common cold.
- The study, involving Covid-19 patients and healthy volunteers, shows that immune cells are activated on contact with the coronavirus.
- In the case of healthy volunteers, this immune system reactivity suggests cross-reactive immunity with mild cold coronaviruses.
- This cross-reactivity could explain why some Covid-19 positive individuals are asymptomatic.
Why, among those affected by Covid-19, some develop severe symptoms while others only have a milder form, or are asymptomatic ?
The question torments scientists around the world and is the subject of much research. Among these, a study conducted by the Charité University Hospital and the Max Planck Institute for Molecular Genetics located in Berlin (Germany) and published in the journal Nature advances an answer: past exposure to cold coronaviruses would allow some individuals to possess immune cells against SARS-CoV-2.
This finding is based on research involving helper T cells, a type of specialized white blood cell that is essential for regulating our immune response. The researchers found that one in three people who have never been exposed to SARS-CoV-2 have T helper cells that can recognize the virus. According to them, this is in particular because SARS-CoV-2 shares certain structural similarities with the coronaviruses responsible for the common cold.
Cross-reactivity of immune cells
To reach this conclusion, the researchers first isolated T cells from the blood of 18 people with Covid-19, then from the blood of 68 healthy people who had never been exposed to the new coronavirus.
The researchers then stimulated these immune cells using small synthetic fragments of SARS-CoV-2 “spike proteins”, those characteristic crown-like protrusions on the outer surface of coronaviruses that allow the virus to enter human cells. .
Then, the T cells were brought into contact with these protein fragments: in 15 of the 18 patients (85%) with Covid-19, the T cells were activated. A reaction that the researchers expected. “The immune system of these patients was fighting this new virus, and therefore showed the same reaction in vitro”, explains Dr. Claudia Giesecke-Thiel, co-author of the work.
But, to the researchers’ surprise, T cells were also able to recognize SARS-CoV-2 fragments in 24 of the 68 healthy people tested (35%). “This suggests that healthy people’s helper T cells are responding to SARS-CoV-2 due to previous exposure to endemic cold coronaviruses.”says Claudia Giesecke-Thiel.
She goes on to explain that one of the characteristics of helper T cells is that they are not only activated by a pathogen”exactly suitable“, but also by pathogens “sufficiently similar”. In this specific case, helper T cells from healthy participants who responded to SARS-CoV-2 fragments were previously activated by cold coronaviruses, showing a “cross-reactivity”.
A possible protective effect
What are the effects of this cross-reactivity? “In general, it is possible that cross-reacting helper T cells have a protective effect, for example by helping the immune system to accelerate its production of antibodies against the new virus.says Professor Leif Erik Sander, co-author of the study. In this case, a recent outbreak of the common cold would likely result in less severe Covid-19 symptoms.”
Nevertheless, “it is also possible that cross-reactive immunity could result in a misdirected immune response and potentially negative effects on the clinical course of Covid-19. We know this can happen with dengue fever, for example”continues the researcher.
New research is now needed to determine whether previous cold coronavirus infections confer protection against subsequent infection with SARS-CoV-2 and whether this can explain the wide variability in clinical manifestations. They will be carried out as part of the “Charité Corona Cross” study.
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