Anyone who is infected with the Sars-CoV-2 coronavirus either stays so fit that they do not even notice, or struggles with mild symptoms for a few days or becomes seriously ill or has health problems for months or even dies. It is difficult to clarify in detail why an infection with Sars-CoV-2, as with other viruses, can run so differently. The individual’s immune reaction to the pathogen plays the decisive role.
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One theory is that previous infections with other coronaviruses, which have long been circulating as cold pathogens, influence the immune response to Sars-CoV-2 – and thus the severity of the disease.
In a in the science magazine “Science” In the published study, a team of researchers took a closer look at what are known as T cells, a part of the immune system.
Various studies have shown a clear reaction of T cells to components of the virus in 20 to 50 percent of people who have never been proven to have been infected with Sars-CoV-2. There are different subtypes of T cells that do different jobs: some T cells activate other parts of the immune system and thus promote the immune reaction, others suppress it, and others kill infected cells. So-called T memory cells persist after an infection or vaccination and can promote the immune response if the pathogen is encountered again.
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Everyone has different memory T cells, depending on which illnesses and vaccinations they have received. In addition, not every person forms the same memory cells against a certain pathogen, but different ones.
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The group around Jose Mateus from the La Jolla Institute for Immunology in the US state of California wanted to find out whether T cells – or some of them – respond equally to certain components of conventional cold coronaviruses and Sars-CoV-2. To do this, they used, among other things, blood samples from people that were taken a few years ago, when the test subjects could not have had any contact with the novel coronavirus.
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Put simply, they presented these cells with small sections of virus proteins, so-called epitopes, to which the immune cells react – or not. For Sars-CoV-2, the researchers identified 142 epitopes in this study to which immune cells from the blood samples respond. After further experimentation, the team concluded that the cells that were responding were most likely memory T cells that formed after a coronavirus-induced cold. This is also plausible because some of the epitopes of Sars-CoV-2 are extremely similar to those of the cold coronaviruses.
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The important question that cannot be answered yet
Do these memory cells help some people get through a Sars-CoV-2 infection without any problems? Unfortunately, that cannot be answered yet. The team led by Jose Mateus writes: “The hypothesis is plausible that already existing T memory cells can contribute to the fact that Covid-19 has different degrees of difficulty – but at this point in time this is highly speculative.”
Because unfortunately it cannot even be clearly stated whether this immune reminder is always beneficial in the case of a Sars-CoV-2 infection. We know that in some cases an earlier illness with a similar pathogen can even be a disadvantage, because the memory, so to speak, directs the new immune response into already established paths – and that does not always have to be the best.
So far, there is no direct evidence that this negative consequence plays a role in Sars-CoV-2 infections, but one must at least consider it wrote two researchers recently published in the journal “Nature Reviews Immunology”.
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