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Why some people who didn’t have Covid-19 may already have some immunity



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

So how could their immune system have reactive T cells if they never had Covid-19? They were “probably obtained from previous infections with endemic” coronaviruses, in which researchers from various institutions in Germany and the United Kingdom wrote a new study. The use of this T-cell memory from another but similar infection as a response to a new infection is called “cross-reactivity”

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“The big question is … to understand what the role of these T cells might be”

The new study included 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 detected in 83% of Covid-19 patients.

While the researchers also found pre-existing cross-reactive T cells in healthy donors, the study wrote that the effect of these cells on the outcome of Covid-19 still remains unknown.

The findings of the study certainly require further research, said Dr. Amesh Adalja, a researcher at Johns Hopkins University for Health Security, who did not participate in the new study.

“In this study, there appears to be a significant proportion of individuals who have this cross-reactive T-cell immunity to other coronavirus infections, which may have some effect on how they eat the new coronavirus. I think the big question is trying to jump from the fact that they have these T cells to understand what the role of these T cells could be, “said Adalja.

“For example, we know that children and younger adults are relatively spared from the serious consequences of this disease, and I think one hypothesis could be that existing T cells may be much more numerous or more active at a younger age. cohorts as in older cohorts, “said Adalja.

“And if you could compare people with severe and mild disease and try and look at T cells in these individuals and say, ‘People who have a serious disease are less likely to have cross-reactive T cells, compared to people who have a mild illness? more cross-reactive T cells? ‘I think this hypothesis is biologically acceptable, “he said. “Obviously, the presence of T-cells does not prevent people from becoming infected, but does it modulate the severity of the infection?” It seems that this may be the case. “

To date, 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 specialist Dr. William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt University School of Medicine in Nashville, who did not participate in the new study, said T cells could not be overlooked.

“Here is a study that suggests that in fact there may be cross-reactivity – if possible pump initiation – with common conventional coronaviruses that cause colds in humans, and there may be some cross-reactivity with Covid virus, which It is interesting in itself, because we thought from the point of view of antibodies that there is not too much cross at all, “said Schaffner.

“It’s not entirely surprising, because they’re all family members. It’s as if they were cousins ​​in the same family, “he said. “Now we need to find out if it has any impact on clinical practice. … Is a person infected with Covid more or less likely to actually develop the disease? And does it have any consequences for the vaccine? development? “

“Almost everyone in the world has encountered coronavirus”

Adalja added that he was not surprised to see this T cell cross-reactivity in study participants who were not exposed to a new coronavirus called SARS-CoV-2.

“SARS-CoV-2 is the seventh human coronavirus that has been discovered, and four of these human coronaviruses are what we call community coronaviruses, and these four are jointly responsible for 25% of our common colds,” Adalja said. “Almost everyone in the world has encountered coronavirus, and since they are part of the same family, they develop a certain cross-reactive immunity.”

The new study on nature is not the only document to suggest a certain level of pre-existing immunity of some people against the new coronavirus.

Alessandro Sette and Shane Crotty of 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 to the SARS-CoV-2 antigen. groups of peptides, ”based on separate research, however, noted that the source and clinical significance of reactivity remain unknown.

Sette and Crotty wrote that “it is now demonstrated that there is some pre-existing immune reactivity of SARS-CoV-2 in the general population. It is thought that it has not yet been proven that this could be due to immunity against “common colds”. coronaviruses.


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