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



A study published in the journal Nature on Wednesday found that of the 68 healthy German adults who were not exposed to coronavirus, 35% of the patients had T cells that respond 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 had some experience in fighting a similar infection and may use that memory to fight a new infection.

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

“The big question is … to understand what the role of those T cells might be.”
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The new study analyzed blood samples from 18 Covid-19 patients (aged 21 to 81 years) and healthy donors aged 20 to 64 years in Germany. The study found that T cells responsive to coronavirus were detected in 83% of Covid-19 patients.

Although the researchers also identified pre-existing cross-reactive T cells from healthy donors, they wrote in the study that it is still unknown what effect these cells may have on the outcome of Covid-19 disease.

The findings of the study undoubtedly call for more research, Dr. Amesh Adalja, a senior researcher at the Johns Hopkins University Health Security Center, did not participate in the new study.

“This study shows that there are a significant number of individuals with this cross-reactive T cell immunity to other coronavirus infections that may have some impact on how they cope with the new coronavirus. I think the big question is the test. Let’s jump from that. that we have these T cells to understand what the role of those T cells might be, ”said Adalja.

“We know, for example, that children and younger adults are relatively distant from the severe consequences of this disease, and I think one hypothesis may be that there may be many more existing T cells or they may be more active at a younger age. cohorts than in older groups, ”said Adalja.

“And if you could compare people with severe and mild disease and try to look at those individuals’ T cells and say, ‘Do people with severe disease have fewer cross-reactive T cells compared to people with mild disease, perhaps more cross-reactive? T cell? “I think there is a biological validity to this hypothesis,” he said. “Still, it’s clear that the presence of T cells doesn’t stop people from getting infected, but does that change the severity of the infection? That seems to be the case.”

To date, the coronavirus pandemic has focused on Covid-19 antibodies and their role in developing immunity against the disease.

But infectious disease expert Dr. William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt University School of Medicine at Nederville University who did not participate in the new study, said T cells could not go unnoticed.

“Here’s a study that shows that there may actually be cross-reactivity – if necessary, some pump filling – with common conventional coronaviruses that cause colds in humans, and there may be cross-reactivity with the Covid virus that causes. This is intriguing in itself, because from the perspective of antibodies we thought that there is not much cross at all, ”said Schaffner.

“It’s not entirely amazing, because they’re all family members. It’s like they’re cousins ​​in the same family,” he said. “Now we need to find out if it has any effect in clinical practice. … Does it make a person infected with Covido more or less likely to actually get the disease? And does it affect the development of vaccines?”

“Almost everyone in the world is exposed to coronavirus”

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

“SARS-CoV-2 is the seventh human coronavirus detected. Four of the human coronaviruses are what we call community-acquired coronaviruses. All these viruses cause 25% of our colds, ”said Adalja. “Almost everyone in the world is exposed to coronavirus and because they are all part of the same family, some cross-reactive immunity develops.”

The new Nature study is not the only document that indicates a certain level of immunity for some people during the new coronavirus.

Alessandro Sette and Shane Crotty, both from the University of California, San Diego, wrote in a comment earlier this month in the journal Nature that “20-50% of unidentified donors have a high response to the SARS-CoV-2 antigen. peptide pools ”based on separate studies, but noted that the source and clinical significance of the reactivity remain unknown.

Sette and Crotty wrote that “SARS-CoV-2 immune reactivity has now been found to exist to some extent in the general population. It is suspected, but not yet proven, that this may be due to immunity” to the common cold. coronaviruses.


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