A flurry of recent studies has revealed that a large proportion of the population – between 20 and 50 percent in some places – can harbor immune killers, called T lymphocytes., who recognize the new coronavirus, although they have never treated it “personally”.
Most likely, these T cells, which lived in people’s bloodstream long before the start of the pandemic, were left to wander after a battle with other related coronaviruses, including four that often cause the flu. It is a case of family resemblance: for the immune system, microorganisms that share origins can be similar, to the point that, when such a cousin visits us, the body sometimes smells its intentions..
The presence of these T lymphocytes puzzled experts, who said it was too early to say whether these cells would play a useful, harmful or absolutely negligible role in the global battle against the new coronavirus. But if these cross-immunized lymphocytes have an influence, however modest, on the immune response to the COVID-19 coronavirus, then they could make the disease less serious, and maybe that could also explain why some people get the virus and stay very sick, while others hardly feel it.
“If you have a population of T lymphocytes armed and ready to protect yourself, you will be able to control the infection better than someone who does not have these cells with cross-immunity.”Explained Marion Pepper, an immunologist at the University of Washington who studies the immune response in patients with COVID-19. “This is what we all hope for.”
T lymphocytes are very agitated cells. Each spends his whole life waiting for a very specific trigger, like a dangerous and threatening virus. As soon as the switch is triggered, the T lymphocyte will clone into an army of specialized soldiers, all with their sights on the same target. Some T lymphocytes are microscopic killers, designed to destroy infected cells; Other primary immune cells called B lymphocytes to produce antibodies that attack viruses.
The first time the virus infects the body, the response is slow; It takes several days for the immune system to decide which T cells are best suited for the mission. But subsequent encounters often elicit stronger and faster responses, thanks to a pool of T lymphocytes, called memory T lymphocytes, that remain even after the initial threat has passed and are ready to take up arms when necessary.
The process usually works best when T cells have to fight the same pathogen repeatedly. However, these recruits are more flexible than we sometimes think, said Laura Su, an immunologist and T lymphocyte specialist at the University of Pennsylvania. When these cells encounter something very similar to the microorganism of their choice, the encounter leads them to fight, even if the invader is a perfect stranger.
In theory, crossed immunized T cells can “protect almost like a vaccine,” said Smita Iyer, an immunologist at the University of California, Davis campus, who studies immune responses to the new coronavirus in primates.. Some previous research has shown that cross-immunized T cells can protect people from different strains of the flu virus and perhaps give some immunity to the viruses that cause dengue and zika, with whom you share a family tree.
The case of coronaviruses is much less obvious, said Alessandro Sette, an immunologist at the La Jolla Institute for Immunology who is in charge of several investigations that study T lymphocytes with crossed immunity to the new coronavirus. Researchers have found people in the United States, Germany, the Netherlands, Singapore and the United Kingdom who have never been exposed to the new coronavirus, but who have T cells that react to it in the laboratory.
Researchers are eager to understand the history of these T lymphocytes, as this may reveal who is most likely to have them. A growing body of evidence, including data that Sette and his colleagues published this week in the journal Science, points to the coronaviruses that cause flu as a potential source. But even unrelated viruses sometimes share similar characteristics, and researchers may never know for sure what “led them to develop,” said Avery August, an immunologist and T lymphocyte specialist at Cornell University.
Regardless of the origin of T lymphocytes, their mere existence can be good news. T lymphocytes are not the only thing that makes up the immune system, but even some pre-existing immunity may mean that people who have had the flu recently could more easily fight against a more perverse member of the coronavirus clan.
Cross immunity in T lymphocytes is probably not enough to prevent infections or diseases. But it can alleviate the symptoms of COVID-19 in people who carry them, or it can increase the protection provided by a vaccine.
“That would be great,” said Iyer.
T lymphocytes are also excellent conductors. Depending on the signals they send, they can synchronize cells and molecules from different parts of the immune system to coordinate a team attack or disable those attacks to get the body back to its normal state.. If cross-immunized T cells are found to prefer to silence the response, they can suppress a person’s immune defense before they even have a chance to fight, August said.
But on the other hand, there are many types of T lymphocytes and they all operate as part of a complex immune system. “It seems that some people want to say that this is ‘good’ or ‘bad’. It is certainly more complex than that, ”said Su.
ç. 2020 The New York Times Company