Infections with the new coronavirus or vaccinations, on the other hand, lead to strong antibody reactions against SARS-CoV-2. Immune reactions against other human coronaviruses, which mostly only lead to harmless colds, also give a certain protection against SARS-CoV-2.
Such cross-reactions are an important piece of the puzzle for comprehensive coronavirus immunity, as researchers from the University of Zurich show.
In order to cope with the Covid-19 pandemic, the population’s immune protection against SARS-CoV-2, which is built up either by vaccination or by infection with the virus, is crucial.
A research team led by the University of Zurich (UZH) has now identified another component that contributes to SARS-CoV-2 immunity: existing antibody reactions against other, harmless coronaviruses.
“People who have pronounced immune responses against human coronaviruses are also protected to a certain extent against infection with SARS-CoV-2,” says Alexandra Trkola, head of the Institute for Medical Virology at UZH.
To do this, the researchers used a specially developed test method to analyze the amount of different antibodies against the four other currently circulating human coronaviruses in the blood serum of 825 donors from the time before the occurrence of SARS-CoV-2. On the other hand, they examined 389 samples from donors who had become infected with SARS-CoV-2.
Combined with computer-aided modeling, this analysis enables precise predictions of how well the antibodies bind to invading viruses and neutralize them.
Cross-acting antibody reactions reduce severe courses
The researchers were able to show that people who were infected with SARS-CoV-2 had lower levels of antibodies against the common cold coronavirus. In addition, SARS-CoV-2 infected people with high antibody levels against the harmless coronaviruses had to be hospitalized less frequently.
“According to our results, a stronger antibody reaction against human coronaviruses also leads to higher amounts of antibodies against SARS-CoV-2. A person who has immunity against harmless coronaviruses is thus better protected against severe courses of SARS-CoV-2 infections, “says Trkola.
This is known as a cross reaction. This also occurs in the immune reaction of T cells, the second pillar of the human immune system.
People only have complete protection against SARS-CoV-2 at the beginning after an infection or after an effective vaccination. Because then the levels of antibodies against the virus are still very high. If their concentration drops over time, infection is no longer prevented, but the memory cells reactivate the immune system – both antibody production and T-cell defense – quickly.
“Immune reactions specifically directed against SARS-CoV-2 that originate from memory cells are of course far more effective than cross-reactive ones. But although the protection is not complete, cross-reactions shorten the course of the disease and lessen its severity. And that’s exactly what we achieve with vaccinations, only much, much more efficiently, ”Trkola emphasizes.
On the way to comprehensive protection against coronaviruses
It remains to be seen whether the cross-reactivity also works the other way round. So whether immunity against SARS-CoV-2 – for example through a vaccination – also protects against other human coronaviruses.
“If SARS-CoV-2 immunity also offers a certain protection against infection from other coronaviruses, we would come a big step closer to comprehensive protection against coronaviruses, including newly emerging variants,” said the virologist.
This assumption is also supported by the fact that a cross-reactive protective effect is not only based on antibodies, but very likely also on T cells.
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