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Because some people who did not have Covid-19 may already have some immunity



The study, published in the journal Nature on Wednesday, found that among a sample of 68 healthy adults in Germany who had not been exposed to the coronavirus, 35% had T cells in their blood that were reactive to -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 had some previous experience fighting a similar infection and may use that memory to help fight a new infection.

So how could their immune system have reactive T cells if they never had Covid-19? Probably acquired in previous “endemic” coronavirus infections, the researchers – from various institutions in Germany and the United Kingdom ̵

1; wrote in the new study. The use of this memory of T cells from another infection that still resembles to respond to a new infection are called “cross-reactivity.”

“The big question is … do you understand what the role of those T cells is?”

The new study involved analysis of blood samples from 18 Covid-19 patients, aged 21 to 81 years, and healthy donors, aged 20 to 64 years, based in Germany. The study found that coronavirus-reactive T cells were noted in 83% of Covid-19 patients.

While the researchers also found pre-existing reactive T cells in healthy donors, they wrote in the study that the impact these cells may have on the outcome of Covid-19 disease is still unknown.

The study’s findings certainly called for more research, said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security, who was not involved in the new study.

“It appears in this study that there is a significant proportion of individuals who have this reactive T cell immunity from other coronavirus infections that may have an impact on how they go with the new coronavirus. I think the question the big thing is to try to jump from the fact that they have these T cells to understand what the role of those T cells is, ”said Adalja.

“We know, for example, that children and younger adults are relatively relieved of the severe consequences of this disease, and I think one hypothesis might be that pre-existing T cells may be much more numerous or more active in younger cohorts than in older cohorts, “said Adalja.

“And if you can compare people maybe with severe and mild disease and try to look at the T cells in those individuals and say,‘ They are people with severe disease less likely to have reactive T cells against people who have disease perhaps have more transverse reactive T cells? “I think there is biological plausibility for that hypothesis,” he said. “It is clear though that the presence of T cells does not stop people from becoming infected, but modulates the severity of infection? That seems to be the case. “

So far during the coronavirus pandemic, much attention has been paid to Covid-19 antibodies and the role they play in building immunity against the disease.

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

“Here’s a study that suggests there may actually be some cross-reactivity – some of the pump hijacking if you will – with normal conventional coronavirus causing colds in humans and there may be some cross-reactivity with the virus “Covid is causing so much damage. That’s in itself and intriguing because we thought from an antibody perspective that there wasn’t so much cross,” Schaffner said.

“It’s not entirely surprising because they’re all family members. It’s like they’re cousins ​​in the same family,” he said. “Now we have to see if there is any impact of this in clinical practice … Does it make it more or less likely that the person who is infected with Covid will actually develop a disease? And does it have any implications for the vaccine? Development?”

“Almost everyone in the world has had a coronavirus encounter”

Adalja added that he was not surprised to see this T-cell cross-reactivity in study participants who had not been exposed to the new rilavirus, named SARS-CoV-2.

“SARS-CoV-2 is the seventh human coronavirus to be discovered, and four of the human coronaviruses are what we call community-acquired coronaviruses, and together those four are responsible for 25% of our common colds, said Adalia. “Almost every person in the world has had some encounter with coronavirus, and since they are all part of the same family, there is some cross-reactive immunity that develops.”

The new study of Nature is not the only document that suggests a certain level of pre-existing immunity among some people for the new coronavirus.

Alessandro Sette and Shane Crotty, both from the University of California, San Diego, wrote in a comment published in the journal Nature earlier this month, that “20–50% of unexposed donors show significant reactivity for the SARS-CoV-2 antigen collections of peptides, “based on separate research – but noted that the source and clinical relevance of the reactivity is still unknown.

Sette and Crotty wrote that “it is now established that the pre-existing immune reactivity of SARS-CoV-2 exists to some extent in the general population. It is hypothesized, but not yet proven, that this may be due to immunity. for “common wind coronavirus.


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