People who have had the new coronavirus would like to know if they have built up resistance to Covid-19. The RIVM website states that it is not certain whether people can get the disease a second time. How great is that uncertainty? And how can we reduce it?
It is unclear what proportion of people become immune. “There is no figure to that,” said Debbie van Baarle, professor of immunology at UMC Utrecht and affiliated with RIVM. “If someone has not been so ill, it seems unlikely that they can become ill again, but we cannot rule it out.”
The only way you can get absolute certainty is by exposing people to the virus again, says Marjolein van Egmond, professor of immunology at Amsterdam UMC. “But ethically, it’s unacceptable to infect healthy people with a potentially deadly virus that doesn’t have a cure.”
Incidentally, there are already people who want to be voluntarily infected with the virus for vaccine research, but ethicists currently see this as a no-go.
For now, the answers must therefore come from other types of research. Until now, much attention has been paid to the antibodies that neutralize virus particles. Less attention was paid to the rest of the immune system, in which all kinds of cells perform indispensable functions.
“Antibodies and immune cells need each other for a good immune response,” says Van Baarle. “We now need to gain more insight into the role that the different parts of the immune system play in combating this new coronavirus. That is quite a puzzle.”
More recently became clear about one puzzle piece. In the blood of people who experienced a mild variant of covid-19, American scientists found specific immune cells called T cells that recognize the virus.
That makes for hope. “This fits what you expect when the body builds immunity,” says Van Egmond. “The caveat is that we do not yet know whether those cells actually contributed to the recovery. Compare it to finding a bicycle with someone in the shed. Such a find does not prove that someone can cycle. It is plausible, but you know it unsure.”
To better understand whether those cells have helped, Van Baarle wants to know whether there are differences in the cells that you find in people with mild complaints, such as in the American study, and people who were in IC, for example. “That way you gain insight into the type of immune response that ensures that an infection is cleared up properly.”
A puzzle piece that we know little about, according to Van Baarle, is the innate immune system. “It consists of cells that are always ready. They signal the virus very shortly after the infection and they produce signal substances that activate the specific, learned defense system. That learned defense system also produces the antibodies. How the innate immune system acts in an infection with the new coronavirus, we don’t know yet. “
There is also much to learn about the antibodies themselves. “As we age, the number of immune cells plummets,” says Jacques van Dongen, professor of medical immunology at LUMC. “As a result, many elderly people also have fewer cells that gradually make better antibodies after the virus has been recognized and that can specialize as an antibody factory.”
“If you start with fewer of these so-called naive B cells, you have a smaller chance of a cell quickly developing into a ‘factory’ that produces perfectly fitting antibodies. So some people need more time to make good antibodies or succeed there not so good at all. “
Van Dongen wants to be able to predict how much defense systems will have to clear the infection. For this, he is looking for links between the population of naive B cells, the course of the disease, the newly created immune cells and the quality of the antibodies.
Cells with memory
Finally, immunologists want to know which memory cells are produced in which quantities. These are the cells that ensure that new antibodies and specific immune cells are produced in a new infection and that the virus is cleared up quickly.
The puzzle is not just laid out. “This is not a matter of months, but of years,” says Van Baarle. “Every puzzle piece now helps vaccine development. If you know what needs to be done in the body to clear the virus, you can control it with your vaccine.”