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The immune system in the fight against Corona | Knowledge & Environment | DW

How does our immune system react to the coronavirus?

Like any virus, the corona virus is little more than a shell around genetic material and a few proteins. To multiply, it needs a host in the form of a living cell. Once infected, it does what the virus commands: copy, assemble, release.

But that doesn’t go unnoticed. Within a few minutes, the body’s immune system intervenes with its innate answer: Granulocytes, phagocytes and killer cells flow from the blood and lymph channels to fight the virus. They are supported by numerous plasma proteins that either serve as messenger substances or help to destroy the virus.

With many viruses and bacteria, this first activity of the immune system is already sufficient to fight an intruder. This often happens very quickly and efficiently. We feel that the system is working: we have a cold, we have a fever.

Symbolic picture flu wave (picture-alliance / dpa / A. Gebert)

How our immune system affects us

A subset of the signal proteins that are normally secreted by infected cells are the interferons. SARS-CoV-1, which is responsible for the SARS epidemic in 2003, appears to have suppressed the production of one of these interferons and thereby at least delayed the attraction of immune cells. To what extent this is also the case with SARS-CoV-2 is so far unclear. However, interferons support the body’s own virus defense and are now being tested as therapy in clinical studies.

At some point, however, the host response is so strong that its effect can be counterproductive. For example, numerous immune cells flow into our lungs and cause the thin land bridge over which oxygen from the air normally passes into the blood to thicken. Gas exchange is restricted, in the worst case ventilation is necessary.

Sometimes the reaction can overshoot and also target healthy cells. This could also be the case with the corona virus. Therefore, drugs are also being tried that suppress an excessive immune response and that are already known from the treatment of autoimmune diseases. The balance between protective and too aggressive immune processes in coping with the coronavirus is currently a great mystery. This must now be researched, says Achim Hörauf, Director of the Institute for Medical Microbiology, Immunology and Parasitology at the University of Bonn.

Defense system of human DE

The acquired immune system starts moving with a time delay. It is different for every person and depends on what we have experienced and which pathogens we have come into contact with. While T cells help destroy infected cells, B cells form antibodies that can keep the virus at bay. In the case of the coronavirus, these are neutralizing antibodies that bind to the spike protein of the coronavirus. This is the point of attack of the virus with which it penetrates the host, i.e. our human cell. Neutralizing antibodies specifically target the spike protein. Our immune system remembers the antibodies it has made and is thus prepared for a new infection with the same intruder.

Is there immunity? How long does it last?

The good news: it is very likely that there is immunity. This suggests the proximity to other viruses, epidemiological data and animal experiments. Soresearchers infected four rhesus monkeys, a species close to humans, with SARS-CoV-2. The monkeys showed symptoms of Covid-19, the coronavirus disease, developed neutralizing antibodies and recovered after a few days. When the recovered animals were infected with the virus again, they no longer developed symptoms: they were immune.

Monkey in New Delhi grid (AP)

Rhesus monkey

The bad news: you don’t (yet) know how long immunity lasts. It depends on whether a patient has successfully trained neutralizing antibodies. Achim Hörauf estimates that immunity should last at least a year. Within this year, each new contact with the virus acts like a booster vaccination, which in turn could extend immunity.

“The virus is so new that nobody has a reasonable immune response,” says the immunologist. He believes lifelong immunity is unlikely. This “privilege” is reserved for viruses that remain in the body for a long time and give our immune system an almost permanent opportunity to get to know it. Since the corona virus is an RNA (and not a DNA) virus, it cannot settle permanently in the body, says Hörauf.

The Heidelberg immunologist Stefan Meuer predicts that the corona virus will also mutate like all viruses. He suspects that this could be the case in 10 to 15 years: “At some point, the acquired immunity will be of no use to us because another coronavirus will come back, against which the protection that has now been formed will not help us because the virus has changed so much that the antibodies are no longer responsible. And then no vaccination will help either. “

How can you take advantage of the immune system’s antibody response?

Researchers are already collecting the plasma from people who have successfully survived an infection with SARS-CoV-2 and are thus treating patients with Covid-19 to a limited extent. The underlying principle: passive immunization. The studies carried out to date have shown positive results so far, but have mostly only been carried out on a few people.

Germany Coronavirus - life science company Yumab ​​(picture-alliance / dpa / P. Spata)

Research on antibodies is in full swing

At best, passive immunization should only be used when a patient’s own immune system has already started to work against the virus, Achim Hörauf says: “The longer you can leave the patient alone with the infection before you start passive immunization protects the better. ” Only through active immunization can you be protected in the long term. At the same time, it is difficult to recognize this point in time.

So far, PCR tests have been used to investigate whether a person has the coronavirus. With the help of a PCR, it is not possible to say whether or not there is reproducible virus RNA. It is a pure proof of whether virus is still present. Dead or alive. A PCR test cannot say whether our immune system has already intervened, i.e. we have had contact with the virus in the past, have formed antibodies and are now protected. Researchers are therefore working on tests that test our blood for the presence of antibodies. They are already in use in Singapore, for example, and are about to be completed in the USA. With the help of these tests, one could finally get an overview of the unclear number of cases. In addition, people who have developed antibodies against the virus could, for example, be used “in the front line” in healthcare. There is even an “immunity pass” in the discussion.

Coronavirus - Berlin - Bayer plans to set up test laboratory in Berlin (picture-alliance / dpa / Bayer AG)

PCR analysis in the laboratory

Can I get infected and / or get corona several times?

“According to everything we know, the same pathogen is not possible,” says Achim Hörauf. You can become infected with other corona viruses or viruses from the SARS or MERS group if their spike proteins look different, “as far as the current epidemic is concerned, it can be assumed that the people who went through Covid-19 , no longer fall ill with it and the virus is not transmitted. “

When are you no longer contagious?

A Study carried out on the first corona patients in Germany, showed that no reproductive viruses can be found from day eight after the onset of symptoms, even if up to 100,000 gene copies per sample can still be detected in the PCR. This could change the previous quarantine recommendations in the future.

Coronavirus in Germany Elmshorn doctor at drive-in test station (picture-alliance / dpa / D. Reinhardt)

A doctor takes a smear

According to the Robert Koch Institute, patients can so far be discharged from the hospital if they have two negative PCR samples from their throat within 24 hours. If they had a severe course, they should remain in home isolation for another two weeks. For every discharge, whether from the hospital or domestic isolation, you should be symptom-free for at least 48 hours.

Why do people react differently to the virus?

While some people get away with a mild cold, others become ventilated or even die from SARS-Cov-2. In particular, people with pre-existing diseases and the elderly seem to be more often inferior to the virus. Why? That’s the hottest question right now.

It will take a very, very long time to understand the mechanistic, biological foundations of why some people are affected so much more than others, virologist Angela Rasmussen told The Scientist. “The virus is important, but the host response is at least as important, if not more important,” her colleague Stanley Perlman told the magazine.

Stefan Meuer sees the different equipment and activity of our immune systems as a fundamental principle of survival in nature: “If we were all the same, one and the same virus could exterminate the whole human species at once.” Due to the genetic range, it is quite normal for some people to die from a viral disease, while others do not even notice it.

Achim Hörauf also suspects immunological variants that could be genetically determined. Since an interstitial pneumonia is observed with the coronavirus, an overreaction of the immune system is probably in the foreground. However, each affected person could also have been loaded with a different dose of virus, which in turn has different courses. And finally, it makes a difference how robust your body and lungs are. Competitive athletes simply have more lung volume than long-time smokers.

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