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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 - perhaps helping to reduce the severity of the disease if that person does indeed get COVID-19. MSN.

Photo: Shutterstock

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 in this study, a significant proportion of people had cross-reactive T-cell immunity against other coronavirus infections, which may have some impact on their lives with the novel coronavirus. I think the big question is to understand what the role of these T cells is, ”Adalya 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 might be that pre-existing T cells may be much more abundant or more active at a younger age. than in the older one, ”the expert added. - If you could compare people with severe and minor illnesses, try to look at the T cells in these people, you would determine that people with severe illness are less likely to have cross-reactive T cells than people with mild illness who have perhaps more of these T cells. There is biological plausibility in 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 there might actually be some cross-reactivity with the common coronaviruses that cause the common cold in humans, and there could be some cross-reactivity with the COVID virus causing so much damage. This in itself is intriguing because we thought of immunity in terms of antibodies, assuming there was no particular overlap, ”Schaffner said.

“This is not entirely surprising, because they are all members of the same family. 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 this increase the likelihood that a person infected with COVID will actually develop the disease? And does this have any meaning for the development of 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 out of seven human coronaviruses are what we call community-acquired coronaviruses, and together they are responsible for 25% of our common colds, Adalya said. “Almost everyone in the world has been exposed to the coronavirus, and since all of these viruses are members of the same family, there is a possibility of developing cross-reactive immunity.”

The new study isn't the only one proposing a theory that some people have a certain level of immunity 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. ”

Miscellaneous immunity Educational program coronavirus Special Projects COVID-19

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