How T-lymphocytes will save us from coronavirus and why they are better than antibodies

By | March 8, 2021

The pandemic WE ALL HAVE LEARNED A LITTLE more care of their health. And in the same way, they began to understand a little better about what they did not even suspect before : the structure of the human immune system, its interaction with viruses of different types and antibodies. The latter are especially interesting in the context of acquired immunity, which allows those who have been ill with COVID-19 (some more, some less) to remain protected from the coronavirus.

But that’s what the problem is: not at all people with symptoms of coronavirus antibodies are detected. How is this possible? The answer to the asterisk problem was T-lymphocytes. Scientists have already proven that the protection they form can be stronger and more perfect. Let’s talk about all this in a little more detail.

Congenital and adaptive immunity

The immune system is a complex network of interconnected cells that protects the body from internal and external threats. In this case, the immunity itself is of two types : innate (natural) and adaptive (acquired). In Basically, they differ from each other specificity and rapid response to the enemy.

Innate immunity is our first line of defense. It can detect many pathogens as soon as they enter the body. But, firstly, she does not always do it fast enough so that we do not have time to get sick, and secondly, she still can not recognize all potentially dangerous molecules.

If something goes wrong and the innate immune system fails, the system sends signals to activate the adaptive immune system. This process is called antigen presentation , because the components of the natural immune system literally present the antigen captured by them to T-lymphocytes (except perhaps without the words “Now this is your problem”).

The adaptive immune system has evolved to provide the body with better defenses. But its full launch is rather slow, so it may take several days before the stars of this party – the T-cells – come into play .

T cells and what you need to know about them

From the school curriculum, many remember that lymphocytes are responsible for our immunity . There are two types of lymphocytes : B cells, which form and mature in the bone marrow, and T cells, which also form in the bone marrow, but mature in the thymus gland (thymus) located in the upper chest. In the body, they work together, but T cells are still cooler.

The fact is that T cells are aimed at identifying and eliminating specific foreign particles. Instead of attacking all antigens in a row (and these are bacteria, viruses, toxins and even pollen – everything that causes the body to produce antibodies), T cells circulate until they encounter “their” antigen. They define it using proteins on the surface that can bind to proteins on the surface of antigens. There are trillions of variants of these surface proteins, each of which can recognize its own target.

The role of T-cells is slightly different in the lifetime. In childhood, with their help, we form immunity to common pathogens and create a supply of memory T-cells. They just remember the reaction to those or other antigens, so meeting them in the future, to respond faster and more efficiently (this is called a secondary immune response). Further, T cells are mainly engaged in immunoregulation and work with repetitive or constantly present (in the presence of chronic diseases) antigens in the body. With age, their number decreases, so the older we are, the weaker our immunity becomes.
T cells also come in different types. Helper T cells, for example, help the activity of other immune cells by releasing cytokine information molecules. They stimulate the maturation of B cells, which are already beginning to produce antibodies to neutralize the pathogen. And killer T cells (cytotoxic T lymphocytes) independently kill damaged or infected cells in the body.

Although T cells are mostly our friends and protectors, sometimes they can cause autoimmune diseases. This happens when cells traveling in search of their antigen begin to attack a person’s own cellular proteins.

What is wrong with antibodies

The main problem with antibodies is that they don’t last very long in the body. There is evidence that the level of antibodies in people infected with SARS-CoV-2 decreases within 2-3 months. It is true that this is not always the case, because the lifespan of antibodies seems to depend on the pathogen.

Antibodies to other coronaviruses can gradually decreasing, maintained from 12 to 52 weeks from the moment of infection. But in the case of a COVID-19, it can last up to seven weeks , and maybe more. Another recent study showed that when the disease is asymptomatic, antibody levels are significantly lower and in 40 % of cases they completely disappear after eight weeks.
It turns out that, even if everything is so with antibodies , the protection they provide is not as long-lasting and powerful as we would like.

T cells and coronavirus

Since most people have never been exposed to the new coronavirus (in fact , he and new), in which there is no T-cell memory and, therefore, protection against infection. The good news is that infected people can generate COVID-specific T cells. Moreover, as shown by a study of Swedish scientists, this also occurs in patients with mild symptoms or no symptoms at all . And even if there are no antibodies in the body .

It was also found that some uninfected people have T cells for COVID-19. This is most likely a cross-reactivity – a coincidence with the body’s response to previous coronavirus infections. When scientists looked at blood samples taken several years before the start of the pandemic, and found T cells in them, adapted to detect proteins on the surface of COVID-19, the theory was confirmed.
Why is everyone so happy about it? Because T-cell reactions can be quite long. When scientists in Singapore analyzed the performance of people who had SARS in 2003 , they saw that even seventeen years later, they still had specific T cells. Not to mention the fact that the presence of T cells more accurately shows whether a person has had a coronavirus or not.

What Russian scientists have found

Most recently, a study by Russian scientists on T cells and coronavirus was published in the authoritative scientific journal Immunity , in which 34 volunteers who had had coronavirus and two control groups of healthy donors took part .

“In fact, not at all ill with coronavirus antibodies are detected. In some of the recovered, the immune response is provided only by T cells, which, apparently, is enough, ” explains Grigory Efimov, head of the transplant immunology laboratory of the National Medical Research Center (NMRC) of Hematology of the Ministry of Health and one of the authors of the study.

Scientists also noted that not only those who have had it have the answer to the fragments of the coronavirus , which may be explained by seasonal colds in the past, which were caused by other types of coronaviruses. “At the same time, healthy donors that we recruited during the pandemic, on average, had a higher response rate than those whose samples were stored in the biobank and received earlier. Most likely, this means that some of the donors had contact with the virus that causes COVID-19 without knowing it, ”adds Grigory Efimov.

One of the most interesting discoveries is the detection of viral fragments, the T-cell response to which occurs most often in humans. According to the researchers, right now they are busy studying these fragments, as a better understanding of them will provide information for the development of a test for T-cell immunity. So far, it is used only as a scientific tool, but if all goes well, it may soon become available for diagnostics too.

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