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



A study published in the journal Nature on Wednesday found that among a sample of 68 healthy German adults who did not experience coronavirus, 35% had blood T cells that responded to the virus.
T cells are part of the immune system and help protect the body from infection. The reactivity of T cells suggests that the immune system may have previous experience in fighting a similar infection and may use this memory to fight a new infection.

So how can their immune system have reactive T cells if they’ve never had Covid-19? They were “probably acquired in previous infections by endemic” coronaviruses, wrote researchers from various institutions in Germany and the United Kingdom in a new study. The use of this T-cell memory from another similar infection to respond to a new infection is called “cross-reactivity”

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“The main issue is understanding what the role of these T cells may be.”

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

Although the researchers also found cross-reactive T cells in healthy donors, they wrote in their study that the effect of these cells on the outcome of Covid-19 disease remains unknown.

The results of the study certainly require further research, said Dr. Amesh Adalya, a senior researcher at the John Hopkins Center for Health, who did not participate in the new study.

“This study finds that a significant proportion of people who have this interactive T-cell immunity to other coronavirus infections may have some influence on how they match the new coronavirus. I think the big question is trying to move away from they have these T cells to understand what the role of these T cells may be, ”Adalya said.

“We know, for example, that children and young people are relatively deprived of the serious consequences of this disease, and I think one hypothesis may be that existing T cells may be much more numerous or active at a younger age in the cohort than in older cohorts, “Adalya said.

“And if you can compare people to possibly severe and mild disease, try looking at those people’s T cells and saying, ‘Are people who have serious illnesses less likely to cross-react with T cells than people?’ who have mild disease may have more cross-responsive T cells? “I think there is biological plausibility in this hypothesis,” he said. That seems to be the case. “

So far, during the coronavirus pandemic, much attention has been paid to antibodies to covidor-19 and their role in the formation of 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 could not go unnoticed.

“Here’s a study that says there may actually be some cross-reaction – some pump refueling, if you will – with the usual coronaviruses that cause colds in humans, and there may be some cross-reaction with the Covid virus that causes so much damage. This in itself is intriguing, because we thought in terms of antibodies that there weren’t many intersections at all, “Schaffner said.

“It’s not very strange, because it’s all family members. It’s like they are cousins ​​in the same family,” he said. “Now we need to understand whether this has an effect in clinical practice … Does it make it more or less likely that a person infected with Kovid will actually develop the disease? And does it have the consequences of vaccination? Development?”

“Almost everyone in the world has been exposed to the coronavirus”

Adalia 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 to be detected. The four human coronaviruses are what we call community-acquired coronaviruses, and these four together account for 25% of our colds,” Adala said. “Virtually everyone in the world has been exposed to the coronavirus, and because they are all in the same family, some cross-reactive immunity develops.”

The new science is not the only document that suggests a certain level of immunity among some people to the new coronavirus.

Alessandro Sette and Shane Crotty, both of the University of California, San Diego, wrote in a commentary published in the journal Nature earlier this month that “20-50% of unaffected donors show significant reactivity to the SARS antigen.” CoV-2 peptide pools “, based on individual studies – but they noted that the source and clinical relevance of the reactivity remain unknown.

Seth and Crotty wrote that “it has now been established that the previous immune reactivity of SARS-CoV-2 in the general population exists to some extent. This is a hypothesis, but has not yet been shown to be related to immunity to the common cold coronavirus.”


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