How does our immune system react to the coronavirus?

Like any virus, the coronavirus is little more than a shell around genetic material and a few proteins. In order to reproduce, it needs a host in the form of a living cell. Once infected, it does what the virus commands: copy, assemble, and release information.

But that does not go unnoticed. Within a few minutes, the body's own immune defense intervenes with its innate response: granulocytes, phagocytes and killer cells flow from the blood and lymphatic vessels 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 initial activity of the immune system is sufficient to fight an intruder. Often this happens very quickly and efficiently. We feel that the system is working: we have a cold, we have a fever.

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

How our immune system makes itself noticeable to us

A subset of the signaling proteins that are normally secreted by infected cells are the interferons. The SARS-CoV-1 responsible for the SARS epidemic in 2003 seems 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 still unclear. However, interferons support the body's own virus defense and are now being tested as a 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 normally passes from the air to the blood, to thicken. The gas exchange is restricted, in the worst case ventilation is necessary.

Sometimes the reaction can overshoot and target healthy cells as well. That could also be the case with the coronavirus. Therefore, drugs are also tried that suppress an excessive immune reaction and that are already known from the treatment of autoimmune diseases. The balance between protective and overly 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.

Human defense system infographic DE

After a time delay, the acquired immune system finally starts moving. It is different for everyone and depends on what we have experienced and what pathogens we have come into contact with. While T cells help destroy infected cells, B cells make antibodies that can keep the virus in check. 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 disable the spike protein. Our immune system remembers the antibodies it has made and is thus prepared for a new infection with the same invader.

Is there any immunity? How long does it last?

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

India rhesus monkey in Uttar Pradesh (picture-alliance / Arco Images / Therin-Weise)

Rhesus monkeys and humans share more than 90 percent of their DNA

The bad news: You don't (yet) know how long your immunity will last. It depends on whether a patient has successfully developed neutralizing antibodies. Achim Hörauf estimates that immunity should last at least a year. Within this year, every new contact with the virus works like a booster vaccination, which in turn can extend immunity.


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


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


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 using it to treat patients suffering from COVID-19 to a limited extent. The underlying principle: Passive immunization . The studies carried out on this have so far shown positive results, but have mostly only been carried out on a few people.


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

Antibody research is in full swing


At best, passive immunization is only used when the patient's own immune system has already started to work against the virus, says Achim Hörauf: "The longer you can leave the patient alone with the infection before you can give them passive immunization protects the better. " It is only through active immunization that one is 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 examine whether a person has contracted the coronavirus. With the help of a PCR one cannot say whether viral RNA capable of replicating is present or not. It is pure proof of whether the virus is still present. Dead or alive. A PCR test cannot say whether our immune system has already intervened, i.e. whether we have had contact with the virus in the past, have formed antibodies and are now protected. Researchers are therefore working on tests that check 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 case numbersbring. In addition, people who have developed antibodies against the virus could, for example, be "in the forefront" in healthcare. There is even an "immunity passport" under discussion.


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

PCR analysis in the laboratory


Can you get infected with corona and / or get sick several times?


"According to everything we know, that cannot be done with the same pathogen," says Achim Hörauf. You could get infected with other coronaviruses or viruses from the SARS or MERS group if their spike proteins look different, "as far as the current epidemic is concerned, you can assume that the people who went through COVID-19 , stop getting sick from it and stop transmitting the virus. "


When are you no longer contagious?


A study carried out on the first corona patients in Germany showed that from day eight after the onset of symptoms, no more replicable viruses that can be grown in cell culture can be found, even if the PCR shows up to 100,000 gene copies per sample can be. This could change the previous recommendations on quarantine in the future. For example, recovering patients could then be discharged from hospitals earlier, which could increase the free bed capacity.


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 currently be discharged from the hospital if they have two negative PCR samples from the throat area within 24 hours. If they had a severe course, they should be kept in isolation at home for an additional two weeks. For every discharge, whether from hospital or isolation from home, one should be symptom-free for at least 48 hours.


Why do people react differently to the virus?


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


It will take a very, very long time to understand the mechanistic, biological basis why some people are so much more severely affected than others, said virologist Angela Rasmussen to "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 a basic survival principle of nature in the different equipment and activity of our immune systems: "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 interstitial pneumonia is observed in the coronavirus, an overreaction of the immune system is likely to be in the foreground. Likewise, each person affected could have been loaded with a different dose of virus, which in turn results in different courses. And finally, it makes a difference how robust your body and lungs are. Competitive athletes simply have more lung volume than longstanding smokers.


Vegetable nutrition icon image

VIRUSES AND BACTERIA HAVE NO CHANCE - WITH A STRONG IMMUNE SYSTEM

Hustle and bustle!

The immune system needs many different fuels. They deliver fruit and vegetables. Eat as colorful as possible: oranges, red peppers, green leafy vegetables, red cabbage provide a colorful potpourri of vitamins and lots of natural vitamin C.

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