October 25, 2020

Could exposure to other coronaviruses protect us against the SARS-CoV-2 virus?


The world has become the global stage for humanity’s fight against the SARS-CoV-2 virus due to the COVID-19 pandemic: confinements, face masks, border closures, schools and establishments, respirators, safety distance, gels hydroalcoholic … At a microscopic level, however, this fight takes place mainly between the new coronavirus and the immune system, and there we humans are a mere battlefield. The long-awaited vaccines, which could end one of the greatest health crises of the century, are nothing more than a tool to train the immune system and thus defeat the coronavirus in the first fight.

Antibody tests are showing us some surprises

Antibody tests are showing us some surprises

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Although the immune system stands out for being a complex biological system that acts with precision against foreign agents, its responses are not without side effects for the human body. General malaise and weakness, headache, or drowsiness are common and unwanted consequences of the response of this system when there is an infection. In the worst cases, the immune system loses the ability to distinguish friends from enemies and triggers diseases: autoimmune disorders (such as lupus or multiple sclerosis) or allergies are the manifestations of this. However, this lack of precision of the immune system does not always have to be harmful. In fact, there is increasing scientific evidence that immune imprecision could have been an unknown ally in this pandemic and, in turn, it could be a tool to use in our favor against the coronavirus.

Since the new coronavirus was identified, multiple researchers raised the possibility that its great genetic similarity to other coronaviruses could make it possible for the immune system of people previously infected with them to respond more effectively to the SARS-CoV-2 virus, avoiding partially or totally COVID-19 disease. In fact, this virus shares 80% of its genome with the SARS virus, which caused an epidemic of severe acute respiratory syndrome in Asia in 2003 and disappeared. Would people who passed this disease be protected against COVID-19? The truth is that we still do not know for sure, but a recent research published in the scientific journal Nature offers more results that reinforce this possibility.

Cross reactivity

The researchers found that people who suffered from SARS 17 years ago (in 2003) not only still had immune cells called memory T cells against the SARS virus, but these lymphocytes also acted against the SARS-CoV-2 virus in vitro. This phenomenon is called cross reactivity. This is what happens when certain key regions of an agent’s proteins (like a virus, in this case) are called epitopes, are the same or very similar to those of other viruses or biological elements. The immune system uses these epitopes as hallmarks to recognize if any element present in the body is a foreign agent.

This study indicates that the signs of identity between the SARS virus and the SARS-CoV-2 are, to a certain extent, similar, and therefore people who already suffered from the first virus could be partially or totally immunized against the new virus. It is still unknown whether this is indeed the case: that there is activity of T lymphocytes against the new coronavirus in laboratory plates does not imply immunity in a person, since many other elements are involved and the response may not be effective enough to stop the coronavirus and avoid infection.

The most surprising finding from research published in Nature is that around 53% of people who had not passed SARS nor had been infected with the SARS-CoV-2 virus also had T lymphocytes that reacted against the new coronavirus, recognizing certain epitopes of various proteins of this new virus. Some of these epitopes bore little resemblance to those found in coronaviruses of the common cold, but were very similar to those found in animal coronaviruses. The authors comment that the distribution of these viruses in different animal species could cause humans to be in contact with them regularly, which would lead to the production of T lymphocytes with the ability to act against the SARS-CoV-2 virus.

“Imprecise” antibodies

These results coincide with those of other recent studies They have found that 20 to 80% of people who have never been exposed to the COVID-19 virus at fault had memory T lymphocytes that reacted to the epitopes of this virus in vitro. In addition, it was also found that a patient who suffered from SARS 17 years ago had an antibody that neutralized the SARS-CoV-2 virus in the laboratory (other studies of patients recovered from SARS and MERS had not found active antibodies against this virus).

The most likely explanation? Exposure to other coronaviruses, such as those of the cold, would generate “imprecise” lymphocytes or antibodies that would also attack the SARS-CoV-2 virus, through a cross reaction. This may explain why some people in close contact with people infected with the coronavirus (such as members of the same family) do not get it.

The key question right now is: Are these people, whose lymphocytes respond to the new coronavirus in the laboratory, partially or fully protected from infection and / or the most severe form of COVID-19? We do not know. And precisely for this reason, different investigations are underway to find out the answer. If the answer was yes, it would be very good news: it would mean that part of the population would be protected, to a certain extent, against COVID-19. Would it then make sense to expose people to cold coronaviruses to protect themselves against COVID-19? At the moment we do not have enough information to know if it could be a good or a bad idea.

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