2023-08-06 04:44:03
Just luck or genetics? Researchers from the USA and Australia have found new clues as to why some people had no corona symptoms.
By Leila Boucheligua, Nina Kunze and Lena Schmidt, SWR
While some people became very ill with Corona, others had no symptoms or only a mild course. But why is that? In a new study, which has now been published in the journal “Nature”, a genetic cause is examined in more detail. The research team from the USA and Australia examined over 1,400 people with a proven corona infection, regarding one in ten of whom had no symptoms. And here they found something in common: an HLA gene variant that not all humans have.
HLA – this stands for Human Leukocyte Antigen. HLA proteins sit on the surface of our white blood cells and perform important functions in the immune system. For example, they help the immune cells to distinguish our own body cells from foreign ones and to recognize pathogens. In the course of evolution, a great genetic diversity has developed in HLA proteins. Some variants are common, while others are very rare. They appear in different combinations.
Protection once morest disease by HLA variants is not new
It has long been known that some HLA variants protect their carriers from certain pathogens. The HLA-B*27 variant, for example, is said to protect once morest influenza viruses and delay the onset of AIDS.
In the study, every fifth person infected without symptoms had the HLA variant called HLA-B*15:01. Some people even carry this variant twice in their genome – once inherited from the mother, once from the father. The variant did not guarantee the participants an asymptomatic course. However, it made a symptom-free corona infection eight times more likely than respondents with other HLA variants.
Other factors also determine the severity of the disease
For their study, the researchers used registered bone marrow donors and asked them to take part in a mobile phone survey regarding their corona symptoms. Particularly practical: Their HLA data has already been recorded as a result of their willingness to donate. Because which variants a person has is particularly important in the case of organ and stem cell transplants. The more similar the HLA variants of the donor and recipient are, the less likely it is that a rejection reaction will occur.
“A very good idea,” says Julian Schulze zur Wiesch, senior physician in the infectiology section at the University Hospital Hamburg-Eppendorf and head of a clinical laboratory that deals with acute and chronic human viral diseases. The weakness of the study, however, is that it was not possible to check all the information once more using the mobile phone survey, according to Schulze zur Wiesch.
He emphasizes that other factors such as age, use of immunosuppressive drugs, previous illnesses and especially vaccinations play a more important role in protection once morest infections and that one should not rely on genetic predisposition.
Evidence of cross immunity
And the study from the USA and Australia provides evidence of another reason why some people had no corona symptoms. The key word: cross-immunity. This term was used once more and once more at the beginning of the pandemic. Because in addition to SARS-CoV-2, there are also the so-called cold corona viruses.
About a third of typical colds are caused by these viruses. The assumption is that anyone who is immune to them is also better protected once morest Covid-19. The research team examined the immune cells of people with the conspicuous HLA variant who stated that they had never been infected with Corona. And indeed: the immune cells reacted to part of the SARS-CoV-2 virus, which is also found in a similar form in common cold coronaviruses.
There are still many unanswered questions regarding Corona
“Even if we thought in 2020 that we had no immune responses, it seems that there was already partial immunity as cross-immunity with other corona viruses,” says Professor Schulze zur Wiesch. Together with other researchers from the University Hospital Hamburg-Eppendorf, the senior physician has also found evidence that an infection with common cold coronaviruses can trigger broad cross-immunity once morest SARS-CoV-2.
However, it is still unclear, explains Schulze zur Wiesch, how long this immunity will last, and even that is no guarantee for a symptom-free course. “It is becoming increasingly clear that there are many interconnections and that an immune system also has a memory, which is very different for all of us,” says the doctor.
And to understand this better, more research is needed – also on Corona, although the pandemic is over. This is important, for example, for people with Long Covid or for many older people and people with previous illnesses who will ask themselves once more in a few months whether they should be vaccinated once morest Corona once more in the fall. In any case, the authors of the “Nature” study hope that their research will provide new insights for therapy and vaccine development.
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