Previous infections with harmless coronaviruses could protect against serious Covid 19 disease. As studies show, the immune system may be “forewarned” as a result.
Covid-19 can range from a mild illness with no or mild symptoms to acute respiratory distress syndrome and death. Why the spectrum in the course of the disease is so broad and what role it plays in it immune system scientists are only slowly beginning to understand.
A research group from the USA could now have found an answer to the question of why the immune response to the pathogen SARS-CoV-2 is not the same for all people. The reason for this could be some kind of background immunity. Because who one cold with other coronaviruses, in which the immune system apparently reacts faster to SARS-CoV-2.
Immune reaction even without infection with corona
As the immunologist Jose Mateus from the La Jolla Institute for Immunology and his colleagues report in the journal “Science”, certain immune cells in the blood react in some people – the T cells – on the new Coronavirus SARS-CoV-2, although those affected have not yet been exposed to this pathogen.
This mechanism of the body’s own defense started in those test subjects who had previously had contact with the spread Cold viruses HCoV-OC43, HcoV-229E, HCoV-NL63, and HcoV-HKU1. These also belong to the group of coronaviruses.
The tasks of T cells in the immune defense
T cells (T lymphocytes) are white blood cells formed in the bone marrow that play an important role in long-term protection against infection. If an infection does occur, the immune system can identify a specific type of pathogen within a few days T cells to produce. If these defense cells of the immune system come into contact with the relevant pathogen, they begin to multiply rapidly, to attach to the infected cells and to destroy them.
For this tailor-made immune response, the T cells different tasks:
T helper cells activate other immune cells through messenger substances and thus initiate the specific defense.
T-Killerzellen identify cells that have been infected by viruses as well as tumor cells and destroy them.
T memory cells arise from the immune response and circulate in the blood even after the infection has been warded off. These cells store how a pathogen was successfully fought and will quickly activate the specific immune system in the event of a renewed infection.
Reports from uninfected sufferers who have the T cells nevertheless reacted to SARS-CoV-2, it had already existed before. The infection experts around Mateus therefore investigated the question of where this came from T cells come.
To do this, they analyzed blood samples from 2019 from test subjects who had not yet come into contact with SARS-CoV-2. They also identified 142 building blocks in the SARS-CoV-2 genome that the immune system recognizes as a threat. The researchers observed that the T cells responded to these components of the virus.
Antibodies against the pathogen are not required for this type of immune reaction. Because T cells cannot produce specific antibodies, but recognize the pathogen itself and attack it.
Whether and to what extent this cross-reactivity affects a possible SARS-CoV-2 infection cannot be answered with certainty by the current “Science” study. The infection experts around Mateus suspect that this mechanism could influence how difficult Covid-19 is.
If this is confirmed, people who have previously had contact with cold pathogens from the coronavirus group would be more likely to be protected from severe Covid-19 courses. According to the study authors, part of the population could be prepared for the new corona virus. In their study, they found in the blood of 20 to 50 percent of the subjects T cells, that can attack SARS-CoV-2.
That T helper cells A team led by immunologist Andreas Thiel from Charité Berlin and the Max Planck Institute for Molecular Genetics had previously discovered the new pathogen when they encountered another coronavirus while having a cold. As the scientists observed, around a third of people who have never been in contact with SARS-CoV-2 still find it T memory cells, who respond to the virus.
T-Help do not respond in all Covid-19 patients
However, the study authors observed that the T helper cells did not respond to the new corona virus in all Covid 19 sufferers. In their analysis published in the journal “Nature” at the end of July, they suspect that the T cells Do not allow activation outside the body in an acute or particularly severe stage of a disease.
The researchers also warn in their study: “What we cannot show: do such cells now protect against SARS-CoV-2 or not?” What effect the activated T cells Charité researchers want to find out in further analyzes on the blood of Covid convalescents.
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