Previous contact with more harmless cold coronaviruses seems to support the immune system in the fight against SARS-Cov-2. However, this effect decreases with age.

6 a.m., September 9, 2021

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Almost everyone has been in contact with more harmless corona viruses ©  Pixel-Shot – stock.adobe.com

Certain immune cells that humans have in the past against cold coronaviruses strengthen them Immune reaction against SARS-CoV-2 – both during natural infection and after vaccination. This is shown by researchers from the Charité Berlin, the Berlin Institute of Health in the Charité and the Max Planck Institute in a current study in the journal Science. This “cross immunity” decreases with age. That could help that elderly people are more likely to get seriously ill with Covid-19 and their vaccination protection is often weaker than for younger people.

Similar structure to viruses

Scientists from the Charité and the MPIMG were the first to make a surprising observation last year: Some people who have never had contact with SARS-CoV-2 have it Memory immune cellswho recognize the pathogen despite its novelty. The team attributed the observation to the fact that these so-called T helper cells dealing with more harmless ones in the past Cold Coronaviruses had to deal with and because of the similar structure, especially des Spike-Proteins on the virus surface, also attack the new coronavirus. Such cross-reactivity has since been established confirmed in a number of studies.

Are in medicine four Coronavirs known that have been circulating in humans for a long time and are endemic humane Coronaviren (HCoV). You call for usually cold symptoms and are called HCoV-OC43, HCoV-229E, HCoV-HKU1 and HCoV-NL63. It is estimated that they make up to 30 percent of colds.

However, the question of how these immune cells were left unclear influence the course of a later SARS-CoV-2 infection. “We assumed that cross-reacting T helper cells have a protective effect, that is, alleviate the symptoms of Covid-19,” says Lucie Loyal, Scientist at Si-M (The Simulated Man). “But it would have the opposite can also be the case. For some viruses, a second infection with a similar virus strain leads to one misdirected immune response, with negative effects on the course of the disease. ”Now the Berlin research team is presenting indications that support the assumption of a protective effect. According to the data, the cross-immunity could be one of several reasons not only for the different severity of Covid-19 courses, but also for different effectiveness of vaccinations in different age groups.

Cross reactions

The researchers almost started recruiting for the study from mid-2020 800 people, who had not yet come into contact with SARS-CoV-2 and checked at regular intervals whether they had become infected with the pathogen. That was the case for 17 people. The research group analyzed their immune systems in detail both before and during the infection. It showed that the body had T-helper cells that it had formed against cold coronaviruses, also mobilized against SARS-CoV-2. In addition, the quality of the immune response against SARS-CoV-2 was better, the more these cross-reacting cells were present before the infection.

The cells recognized it particularly frequently a specific area of ​​the spike protein. The structure of the old and the new coronavirus is “preserved” at this point, that is, it is designed to be particularly similar. “In the case of colds with more harmless coronaviruses, the immune system builds a kind universal, protective coronavirus memory on “, explained Claudia Giesecke-Thiel, lead author of the study. “If it comes into contact with SARS-CoV-2, such memory cells are activated again and now also attack the new pathogen. This could contribute to a faster immune response against SARS-CoV-2, which prevents the virus from spreading unhindered in the body at the beginning of the infection and thus presumably has a positive effect on the course of the disease. “

Vaccination still necessary

The scientist also emphasizes: “This does not mean that past colds definitely protect you from SARS-CoV-2. Vaccination is important in any case. Our study provides one of several explanations for the observation made since the beginning of the pandemic that SARS-CoV-2 infection can develop so differently in different people. “

The scientists also found an immune-boosting effect of the cross-reacting T cells in one Covid-19 vaccination with BioNTech’s vaccine. Similar to a natural infection, the vaccine causes the body to produce the SARS-CoV-2 spike protein and present it to the immune system. An analysis of the immune response of 31 healthy people before and after vaccination showed: During normal T-helper cells over a period of time activated gradually over a period of two weeks, said the cross-reacting helper T cells within a week respond very quickly to the vaccination. This also had a positive effect on the formation of Antibodies Off: After the first vaccination, the body was able to produce antibodies against the conserved spot in the spike protein at a rate that is otherwise only observed with booster vaccinations.

T helper cells are for that Control and coordination of the immune response responsible. If a pathogen penetrates the body, so-called phagocytes pick it up and present fragments of it (“antigens”) on their surface. Helper T cells control these fragments; if they have a more or less suitable receptor for these pathogen fragments, they are activated. Activated T helper cells then ensure that other immune cells attack the pathogen fight directly and form tailor-made antibodies. Most immune responses then also develop so-called T helper memory cells, that can survive in the body for many years and are responsible for a faster and more efficient immune response in the event of renewed contact with the same or similar pathogen.

In a second part of the study, the researchers were able to analyze the T helper cells at just under 570 healthy individuals prove that the Cross immunity decreases in old age: Both the number of cross-reacting T cells and their binding strength were lower in older study participants than in younger ones. the decreasing cross immunity lead the authors to natural changes in one aging immune system return. According to the experts, a third vaccination in this more vulnerable population group, presumably compensate for the weaker immune response and ensure adequate vaccination protection.

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