First indications of cross-immunity through pre-infections with cold corona viruses Corona: Can previous colds protect? – scinexx

Protection or danger? Previous cold coronavirus infection could affect the severity of the course of Covid-19. The defense cells formed during pre-infection also react to the new SARS-CoV-2 coronavirus, as a study has now revealed. The researchers found such T helper cells in about a third of the healthy volunteers tested. A follow-up study will now show whether this cross immunity protects its bearers or not.

Our immune system uses a complex, multi-level defense strategy against pathogens such as the coronavirus SARS-CoV-2. In addition to the production more specific antibody it also uses various defense cells to ward off pathogens against certain surface structures of the virus. These include several types of T cells, which also react to parts of the surface proteins of the virus and coordinate the immune response and antibody production.

T cells in the pathogen test

As it turns out, the presence of certain T cells in some people could have a major impact on the course of Covid-19. Julian Braun from Charité – Universitätsmedizin Berlin and his colleagues discovered this when they examined the behavior of T helper cells from the blood of 18 Covid-19 patients and 68 healthy subjects.

The researchers also confronted them as CD4⁺Defense cells denote T cells with different sections of the spike protein of SARS-CoV-2. As expected, the T helper cells from the blood of most Covid 19 patients responded to the protein parts of the coronavirus. “The patient’s immune system was fighting the new virus and therefore reacted to it in a test tube,” explains co-author Claudia Giesecke-Thiel from the Max Planck Institute for Molecular Genetics.

Reaction also in healthy people

The surprise, however, was that the T cells of some healthy volunteers also reacted to the viral protein pieces. 24 of 68 healthy people – a good third – had T helper cells that recognized SARS-CoV-2 fragments. Accordingly, there are people who have never been in contact with the new corona virus, but whose immune system can still recognize this new virus. But why?

A closer examination of the reaction provided the first clues to the reason: While the T cells of the Covid 19 patients reacted to almost all components of the spike protein, the T cells of the healthy test subjects did not. They were only activated by substructures of the protein that are older in evolution and also occur in other, closely related coronaviruses such as SARS-CoV or the four known cold coronaviruses.

“Forewarned” by cold corona viruses

“This indicates that the healthy T-helper cells react to SARS-CoV-2 because they have had to deal with local cold coronaviruses in the past,” explains Giesecke-Thiel. “Because one property of the T helper cells is that they can not only be activated by an exactly ‘suitable’ pathogen, but also by sufficiently similar intruders.”

In fact, reaction tests with protein parts of the common cold coronavirus showed that the T helper cells of the healthy volunteers responded strongly to them. The research team concludes that around a third of their healthy study participants have had a cold at some point in the past that was caused by one of these harmless cold coronaviruses. T-helper memory cells remain from this infection in the body, which apparently can now also react to the new coronavirus.

“Corona viruses cause up to 30 percent of seasonal colds in Germany,” explains co-author Andreas Thiel of the Charité. “It is estimated that an adult gets an average of one of the four native corona viruses every two to three years.”

Cross-reaction could protect but also make it worse

But what does this cross-reaction mean in relation to Covid-19? “Basically, it is conceivable that cross-reactive T helper cells have a protective effect, for example by helping the body to produce antibodies to the new virus more quickly,” explains co-author Leif Erik Sander from the Charité. “In this case, recent coronavirus colds would likely alleviate the symptoms of COVID-19.”

But it would also be possible that this cross-reactive immunity may even worsen the course of Covisd-19. Because if defense cells or antibodies can dock on a virus but do not fit perfectly on its structure, it can lead to one Wrong reaction of the immune system. In this case, the immune system is unable to neutralize the virus. Instead, the pathogen continues to multiply and at the same time there is an excessive immune response.

Follow-up study is already underway

In a follow-up study, the scientists now want to investigate which of the two options applies. “If we assume that these cold viruses can actually confer a certain immunity to SARS-CoV-2, people who have often suffered from such infections in the past and for whom we can detect cross-reactive T helper cells should be better protected than others “Explains Thiel. “We will therefore pay particular attention to these groups of people in the Charité Corona Cross study.”

At the same time, the research team will also support corona risk groups over the next few months. Finally, the study should help to better predict the course of Covid-19 in the future both before and after SARS-CoV-2 infection. “This is extremely relevant for the everyday life of many people as well as the treatment of patients,” emphasizes Thiel. (Nature, Preprint, doi: 10.1038 / s41586-020-2598-9)

Source: Charité – Universitätsmedizin Berlin

July 30, 2020

– Nadja Podbregar

–