Antibodies are small proteins that adapt precisely to certain surface structures of a pathogen and deactivate it if they attach to it. They are effective, but the immune system has different ways of dealing with pathogens, explains immunologist Leif Erik Sander of Charité Berlin.

“That’s a good thing, because infectious agents are also very different. And antibodies are a very flexible way of dealing with infectious agents. They then bind to the structures of microorganisms, and with viruses it often happens that they bind to them and can neutralize them.

Antibodies intercept invading viruses before they can invade and multiply in our cells. They are formed by a group of so-called B cells when they come into contact with a pathogen and recognize specific structures of this pathogen as foreign.

T lymphocytes: “the second arm of the immune system”

“However, it’s possible that this line of defense has holes and that viruses are still entering the cells,” says Sander. “But there are other ways to kill infected cells, and some T cells are one of them, for example. But there are other innate immune cells that can kill virus-infected cells.

T lymphocytes are the second arm of the “learned immune defense”. They recognize human cells that have already been invaded by pathogens. Thanks to these T lymphocytes, the immune system can eliminate these cells before the virus can multiply there.

And finally, the immune system also forms so-called memory cells. These are immune cells that can remember particular structures of the pathogen or infected cells. If a virus or bacteria invades the body again, the immune system can then react more quickly. In the best case, it kills all pathogens before they can multiply and make the body sick.

The amount of antibodies is easier to measure

“In principle”, explains Leif Erik Sander, “you need the different aspects of the immune system. Only T cells are much more difficult to measure, it’s complicated, because you can’t measure them as directly as you can measure antibodies.”

Therefore, doctors usually only determine the amount of antibodies to find out how well a person is protected after infection or vaccination.

“Antibodies are very easy to measure, they are very simple test systems. And they are also a good indication of how the immune response responded. That’s why you also measure antibodies to say: is there good protection or not.”

Protection against disease even without antibodies

In the case of the SarsCov2 Omikron variant, it has been shown that we need more antibodies in the blood to render the virus harmless. But even if someone doesn’t have antibodies against SarsCov2 in their blood, they can still be protected against the disease.

This is shown, among other things, by a study carried out by researchers at the Karolinska Institute in Stockholm during the first wave of infection with the type of virus that predominated at the time. At the time, they were comparing people with a severe course of Covid with patients who had only mild symptoms. Additionally, the researchers looked at family members from the same household.

Marcus Buggert, group leader at the Center for Infectious Medicine at Karolinska Institutet, is one of the authors of the study.

“We saw that some people in whom we couldn’t measure antibodies had developed T-cell immunity anyway,” he says.

“The most interesting group were family members who had lived with people with Covid but were healthy themselves. Very many of them had developed a T-cell response and some also developed antibodies against the coronavirus, even though they were not sick. And it shows that there is also a kind of partial immunity with this virus which protects us at least a little. For example, before a severe evolution of the Covid.

T-cell immunity may also protect against omicron

This T-cell immunity also appears to provide more robust protection than antibodies against the omicron variant. This is indicated by the results of another study that Marcus Buggert and his team have just published in the journal “Nature”.

The researchers had compared vaccinated people to unvaccinated, recovered people who had been infected with Sars-CoV-2 along with other variants of the virus. It has been found:

“In most individuals, it appears that T cells formed after infection or vaccination can also recognize the omicron variant. Unlike the antibodies formed. In those examined, they were 30 to 40 times worse than the omicron variant.

This could explain why many vaccinated or recovered people are currently infected with the omicron variant, but do not become seriously ill. Without effective antibodies, the virus can still affect the upper respiratory tract. However, acquired immunity from T cells and other immune components apparently prevent the virus from multiplying out of control and then reaching the lower respiratory tract and causing severe respiratory distress.

“Immunity is neither black nor white”

“I think our study shows pretty well that immunity to a virus is not black or white. It’s not just about antibodies, there are many components of the immune system that can protect us against a virus. like Sars-CoV-2.”

The more frequently we come into contact with the coronavirus itself or a vaccine against it, the more robust our immune response becomes. Therefore, the following still applies: the more people are vaccinated against Sars-CoV-2, the better.

“So far, this has at least been confirmed in that people who have been vaccinated have a significantly reduced risk, and those who have been boosted have an even lower risk,” explains Leif Erik Sander.

“It may still look like a real flu – but that would be the hope: that Omikron will now put us in a state where a Sars-CoV-2 infection is no longer too dangerous. That it will be something that can happen from time to time, but that we don’t constantly have to deal with an overload of the health care system and that we don’t have as many people seriously ill from this infection.

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