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Our immune response is like a Swiss Army knife that contains many different tools. Each of them may turn out to be useful in the fight against the coronavirus in its own way. With the disappearance of antibodies, immunity does not disappear. We owe it to T lymphocytes, which identify and destroy virus-infected cells, and live from several months to several years.
Scientists were concerned that with the disappearance of antibodies from our body, it would no longer be protected against further SARS-CoV-2 infections. However, our defense system is based on more than these proteins. White blood cells, and more specifically B lymphocytes, play a special role, which can differentiate into antibody-producing cells and memory cells. Key in the process of defense against the coronavirus are memory T cells, which not only identify and destroy infected cells, but remain in the body after an illness. If the same pathogen reappears, they are prepared to produce large amounts of antibodies in a short time.
Long-lived lymphocytes with the memory of viruses
Research published by the medical journal Cell suggests that anyone who develops COVID-19 (even asymptomatically) produces memory T cells that can fight the coronavirus in the event of a new infection. The authors of the paper say memory lymphocytes will be key to long-term immune protection against COVID-19 as they can prevent recurrent episodes of the disease. This is because these lymphocytes live a very long time after the infection is over, while antibody levels drop quickly.
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Even patients without antibodies have T memory cells
In Sweden, researchers tested the blood of 206 people who had had COVID-19 of varying severity. It was found that regardless of whether a person recovered from mild or severe disease, they still developed a strong immune response in the form of T lymphocytes. Even in patients who were no longer detected for antibodies, memory cells were extracted.
Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, considers T-cell research a success.
“People who do not have high levels of antibodies but have become infected have a T-cell immune response,” he said.
A study published in July this year, and conducted on a group of 36 convalescents, showed the presence of these cells in all of them. Another, which appeared in the journal “Nature”, shows that among 18 German patients with coronavirus, more than 80 percent. T memory cells specific for this particular virus were detected.
People who have not come into contact with SARS-CoV-19 may have type T memory cells
Interestingly, these studies also brought a surprising discovery. Many people who have never had COVID-19 have T memory cells in their bodies that are capable of recognizing the coronavirus. This was the case with more than half of the 37 people in the July study and one third of the 68 patients described in Nature. It is estimated that the situation is similar in some areas of the USA (20-50% of the population).
The phenomenon of cross-reactivity could explain this finding. It occurs when T cells, produced in response to the virus, respond to a similar but previously unknown pathogen. According to experts, cross-reactive T cells most likely come from prior exposure to non-SARS-CoV-2 coronaviruses, e.g. those that cause the common cold.
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This hypothesis is confirmed by another study published in early August this year. Researchers found 25 people who had never had COVID-19 had T memory cells that recognized both the new coronavirus and four other types of common coronavirus.
“This explains why some people have milder symptoms,” says study co-author Alessandro Sette. “They started with some advantage, an advantage in the race between the virus that wants to reproduce and the immune system that wants to eliminate it,” Sette added in an interview with Business Insider.
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Will T-cell immunity be long-term?
While T-cell research looks promising, scientists still don’t know how long survivors will be protected from another COVID-19 infection.
“We’ll find out after some time,” said David Masopust, a fellow in Microbiology and Immunology at the University of Minnesota. – Maybe in five years, more can be said. Today nothing can be predicted.
There are studies which show that T cells were detected “several months after infection in the absence of antibodies”. Others suggest that not only do they persist for at least three months after the onset of coronavirus symptoms, but in some cases are produced in greater amounts during this time.
Based on material collected from observations of other coronaviruses, such as SARS, scientists suggest that the viability of T cells is counted over decades. In blood samples of 23 SARS survivors, memory T cells specific to SARS 17 years ago were found.
Jennifer Gommerman, an immunologist at the University of Toronto, told CNN: “The findings of such a strong immune response mean that a future coronavirus vaccine should offer us long-term protection.”
Read also:
- Resistance to COVID-19 is short-term. It takes 2-3 months
- Why do young people die from COVID-19 and 90-year-olds do?
- The antibodies remain in the blood for about 3 months. Then we can get sick again?
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