Why is immunity to coronavirus found in people who have not had COVID-19

According to a new study, the immune systems of some people who have not been exposed to coronavirus infection may be familiar with the pathogen - possibly helping reduce the severity of the disease if that person does get sick with COVID-19, writes MSN.

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The study, published in the journal Nature on Wednesday July 29, found that among a sample of 68 healthy adults in Germany who were not exposed to the novel coronavirus, 35% had T cells in their blood that reacted 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 previous experience with a similar infection and may use this memory to fight a new virus.

How can the immune systems of these people have reactive T cells if they have never had COVID-19? As scientists from various institutions in Germany and the UK wrote in their study, the cells were "probably acquired from previous infections with endemic coronaviruses." The body's use of this T-cell memory in response to a new infection is called cross-reactivity.

"The big question is to understand the role of these T cells."

The new study included the analysis of blood samples from 18 COVID-19 patients between the ages of 21 and 81 and healthy donors between the ages of 20 and 64 in Germany. The study found that coronavirus-responsive T cells were found in 83% of COVID-19 patients.

Although the researchers also found pre-existing cross-reactive T cells in healthy donors, they wrote in the report that the effect of these cells on COVID-19 disease outcome is still unknown.

The study's findings certainly warrant further clarification, said Dr. Amesh Adala, a senior fellow at Johns Hopkins University's Center for Health Security, who was not involved in the new study.

“It appears that a significant proportion of people in this study had cross-reactive T cell immunity from other coronavirus infections, which may have some impact on their lives with the new coronavirus. I think the big question is to understand what the role of these T cells is,” Adalja said.

"We know, for example, that children and young people are relatively protected from the serious consequences of this disease, and I think one hypothesis may be that pre-existing T cells may be much more numerous or more active at a younger age." than in older ones,” the expert added. “If you could compare people with severe and mild disease and try to look at the T cells in those people, you would find that people with severe disease have less cross-reactive T cells compared to people with mild disease who have , perhaps more of these T cells. There is biological plausibility to this hypothesis. It is clear that the presence of T cells does not prevent people from contracting the virus, but does it affect the severity of the infection? It looks like it is."

On the subject: 'Fragile and short-lived': experts doubt the reliability of immunity to coronavirus

Until now, during the coronavirus pandemic, much attention has been paid to antibodies to COVID-19 and their role in creating immunity against this disease.

But infectious disease expert Dr.William Schaffner, an infectious disease professor at Vanderbilt University in Nashville who was not involved in the new study, said T cells should not be ignored.

“Here's a study that suggests that there may actually be some cross-reactivity with the common coronaviruses that cause colds in people, and there may be some cross-reactivity with the COVID virus that causes so much damage. That in itself is intriguing because we were thinking about immunity in terms of antibodies, suggesting that there wasn't much overlap,” Schaffner said.

“It’s not entirely surprising because they are all members of the same family. It’s like they’re cousins ​​in the same family,” he said. “We now have to see if this has any impact in clinical practice.” Does this make it more likely that a person infected with COVID will actually develop the disease? And does this have any implications for creating a vaccine?”

"Almost every person in the world has encountered a coronavirus"

Adalya added that he was not surprised to see this T-cell cross-reactivity in study participants who were not exposed to the novel SARS-CoV-2 coronavirus.

“SARS-CoV-2 is the seventh human coronavirus to be discovered. Four of the seven human coronaviruses are what we call community acquired coronaviruses, and together they are responsible for 25% of our common colds, Adalja said. “Almost everyone in the world has been exposed to coronavirus, and since these viruses are all members of the same family, there is a possibility of developing cross-reactive immunity.”

The new study is not the only one that suggests a certain level of immunity in some people to the new coronavirus.

On the subject: Measles vaccine may be immune to COVID-19

Alessandro Sette and Shane Crotti of the University of California, San Diego wrote in a commentary on an article published in Nature earlier this month that "20-50% of unaffected donors show significant reactivity to the SARS-CoV-2 antigen." The data were based on separate studies, but they noted that the source and clinical significance of the reactivity remain 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 has been suggested, but not yet proven, that this may be related to immunity to the common cold-causing coronavirus. ”

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