After hope for cross-immunity: Cold viruses do not protect against Covid-19

Who is infected with the cold coronavirus is also better protected against infection with Sars-CoV-2? At least that’s what some experts suspect. But researchers from Kiel are now finding out: cold viruses do not offer better immune protection. On the contrary: they can even be harmful.

Coronaviruses were also in circulation before the Sars-CoV-2 pandemic. For example, they can cause a cold. Experts therefore suspected that earlier contact with these cold viruses could lead to better immune protection against Sars-CoV-2 infection. Researchers from Kiel have now refuted this idea in a study: people who are not yet infected with Sars-CoV-2 would actually have certain immune cells, so-called memory T cells, which also recognize Sars-CoV-2 as foreign bodies. can. However, these memory T cells are not very effective because they bind the virus only weakly.

In their study, the Kiel researchers looked at immune cells in the blood of donors who had previously had no contact with Sars-CoV-2. They found that people without prior contact with the virus have these memory cells that also recognize Sars-CoV-2 as a foreign body. “However, contrary to expectations, younger people who get more colds do not have a higher number of these cells,” says Alexander Scheffold of the University Medical Center Schleswig-Holstein. In addition, only a small proportion of these cells also react with the corona cold viruses.

“It seems more to be the case that over the course of life the repertoire of memory cells against many different pathogens grows and with it the likelihood that there are some who recognize Sars-CoV-2 by chance,” explains Scheffold. This memory cell repertoire, which increases with each infection, may therefore also be referred to as “immunological age”, which actually increases with biological age.

While these memory cells are present in everyone, they are obviously not involved in the defense against Sars-CoV-2 infection. This is probably due to their quality: “These memory T cells recognize Sars-CoV-2 viruses, but they don’t do it very well. As a result, they probably can’t guarantee that the virus will be successfully fought,” says lead author Petra Bacher of the University of Kiel the study results.

Immunological age as a risk factor

The research team found T cells in the blood of patients with Covid 19 with a mild course, who recognize the virus very well. “This could be based on an immune response based on naive T cells, that is, the T cells that support the immune response to the virus here may come from naive T cells and not from memory cells,” explains Bacher. .

It was especially interesting for the researchers that in patients with a severe disease course the T cells recognize Sars-CoV-2 just as poorly as the “pre-existing” memory T cells. “This could indicate that in severe cases of Covid, these immune cells come from the poorly binding pre-existing memory T cells,” says Bacher.

This could be a simple explanation why the elderly are at higher risk of developing the disease more seriously. “In many cases, they also have a higher immunological age and thus a greater chance that the immune system will resort to these ‘incompetent’ memory cells,” says Bacher.

Her colleague Scheffold therefore says, “Our work shows that previous colds with coronaviruses do not provide efficient immune protection against Sars-CoV-2.” In addition, it provides important evidence that immunological age could potentially promote a serious course of Covid-19 disease. “Further research is now needed to verify a direct link between immunological age and severe Covid-19, and to analyze the influence of pre-existing memory cells on the immune response to Sars-CoV-2,” said Scheffold.

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