Why some people who do not have COVID-19 may already have some immunity


The immune system of some people who have not been exposed to novel coronoviruses may have some familiarity with the pathogen – possibly helping to reduce the severity of the disease if the person acquires COVID-19, a new study Tells.

The study, published Wednesday in the journal Nature, found that among a sample of 68 healthy adults in Germany who had not been exposed to coronovirus, 35% had T cells in their blood that were reactive to the virus.

T cells are part of the immune system and help protect the body from infection. T cell reactivity suggests that the immune system may have some experience fighting past infections and that the use of that memory may help fight a new infection.

How could their immune system have reactive T cells if they never had Kovid-19? They were “acquired in previous infections with endemic infections” by researchers from various institutions in Germany and the United Kingdom. Using this T cell memory from another yet identical infection to respond to a new infection is called “cross-reactivity”.

‘The big question is … to understand what the role of those T cells can be’

The new study analyzed blood samples from 18 COVID-19 patients located in Germany, ages 21 to 81, and healthy donors 20 to 64 years. The study found that 83% of COVID-19 patients detected T cells reactive to coronovirus.

While researchers also found cross-reactive T cells already present in healthy donors, they wrote in the study that the effect that COVID-19 disease can have on those cells is still unknown.

The findings of the study certainly call for more research, with senior scholars at the Johns Hopkins University Center for Health Security, Drs. Said Amesh Adalja, who was not involved in the new study.

“It appears in this study that there is a significant proportion of individuals who have this cross-reactive T cell immunity from other coronovirus infections that may have some impact on how they fare with novel coronoviruses. I think The big question is trying. Let’s jump to the fact that they have these T cells to understand what the role of those T cells might be, “said Adalja.

“We know, for example, that children and young adults are relatively spared the serious consequences of this disease, and I think one hypothesis could be that there are already existing T cells that are very young at a young age Or may be more active. Cohorts than middle-aged peers, “said Adalja.

“And if you can compare people with severe and mild disease and try and look at T cells in those people and say, ‘Are people who have severe disease, the possibility of reactive T cells crossing? Is less. More cross-reactive T cells? ‘I think there is biological plausibility for that hypothesis, “he said. “Although it is clear that the presence of a T cell does not prevent people from becoming infected, it does control the severity of the infection. It appears that this may be the case.”

Until now during the coronavirus epidemic, there has been a lot of focus on COVID-19 antibodies and their role in building immunity against the disease.

But infectious disease specialist Drs. William Scheffner, a professor of preventive medicine and infectious diseases at Vanderbilt University School of Medicine in Nashville, who was not involved in the new study, said that T cells cannot be ignored.

“Here’s a study that suggests that there may actually be some cross-reactivity – some priming of the pump if you will – with the usual conventional coronavirus that causes colds in humans and some crosses with the COVID virus -Reactivity can occur. ” So much damage has been done. This in itself is tricky, because we thought from the antibody perspective that there was not much crossing.

“It’s not entirely surprising because all of them are members of one family. It seems like they are cousins ​​in the same family,” he said. “Now we have to see if it has any effect in clinical practice. … Is it more or less likely that the person infected with COVID will actually develop a disease? And whether its vaccine for Is there any effect? ​​Development? “

‘Almost everyone in the world has had some encounter with coronovirus’

Adalja said that he was not surprised to see this T cell cross-reactivity in study participants who were not exposed to the novel coronavirus named SARS-COV-2.

“SARS-COV-2 is the seventh human coronavirus that has been discovered, and there are four of the human coronaviruses that we call community-acquired coronaviruses, and those four are responsible for 25% of our common cold,” Adalja said. “Almost everyone in the world has had some encounters with coronaviruses, and since they are all part of the same family, there is some cross reactive immunity that develops.”

The new nature study is not the only paper to suggest a certain level of immunity already present among some people for novel coronaviruses.

Alessandro Sette and Shane Cratti, both of the University of California, San Diego, wrote in a commentary published earlier this month in the journal Nature that “20–50% of unpublished donors exhibit significant reactivity to SARS-CoV-2 antigens” . Peptide Pool, “based on separate research – but he said that the source and clinical relevance of the reaction remains unknown.

Sete and Crotti have written that “it has now been established that the SARS-CoV-2 pre-existing immune response is present to some extent in the general population. It is hypothesized, but not yet proven, that it is immune The reason may be the “common cold” coronavirus.

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