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Scientists are still wondering why some people are mildly affected by COVID-19, while others are very severe. It is known that the immune system of some people who have never come into contact with SARS-CoV-2 already responds to this virus. Why? It is possible that it is due to colds in the past – such conclusions were brought by a study by scientists from the American La Jolla Institute for Immunology.
The immune system of some healthy people can recognize SARS-CoV-2
The starting point for scientists was the results of previous research carried out by the La Jolla Institute for Immunology. In May, Alessandro Sette described 10 people who had never been exposed to the new coronavirus, but their immune systems had lymphocytes capable of recognizing and responding to SARS-CoV-2. During a broader analysis, the phenomenon was also observed in some of the respondents from the Netherlands, Germany, Great Britain and Singapore.
This is not the only research that shows that part of the human population may have antibodies that respond to SARS-CoV-2, although it has not been exposed to it. One of the results was published last month. It found that of the 68 Germans surveyed who never had COVID-19, more than a third had lymphocytes that reacted to the virus. Another study is published in the journal Nature. It found that more than half of a group of 37 healthy people who had never contracted COVID-19 had T cells capable of recognizing the new coronavirus.
- Why are there people who have not had COVID-19 but are immune to the coronavirus?
The key to the puzzle is the so-called Immune memory, i.e. the body’s ability to respond faster and more effectively when it comes into contact with the antigen (made possible by memory lymphocytes). But how is it that the immune system recognizes SARS-CoV-2, even though it has not been exposed to it?
Scientists believe that SARS-CoV-2-responsive memory T lymphocytes may have arisen due to infection with less dangerous “cousins” of the new coronavirus, which cause the common cold (coronaviruses are responsible for about 10-20 percent of colds).
- One in four infected with the coronavirus has no symptoms of the disease
Scientists recall that T cells are a key part of the body’s defenses against the virus: they identify and destroy infected cells while informing B cells about how to make new antibodies. Antibody levels can drop within months after infection, but memory T cells remain in the body for years. Thanks to them, upon re-contact with the antigen, the immune response is faster and stronger. If such a response occurs in the case of infection with a similar pathogen, we are dealing with the so-called cross resistance.
Immune memory influences patient outcomes with COVID-19? More research needed
To find out, scientists at the La Jolla Institute for Immunology, including Alessandro Sette, analyzed memory T cells from people who had never been exposed to SARS-CoV-2.
They found that their immune system can produce a range of memory T cells that respond to SARS-CoV-2, as well as four other types of coronaviruses that cause the common cold. In other words, infection with the common cold coronavirus can lead to immune cells cross-reacting to SARS-CoV-2. According to Alessandro Sette, this T-cell response makes it possible to fight infection much faster and better.
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‘This may help explain why some people show milder symptoms of the disease while others get seriously ill,’ notes Alessandro Sette, co-author of the new study.
However, the scientist cautions that it is too early to tell if existing immune memory is influencing the outcomes of COVID-19 patients. More research is needed.
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