Since the start of the COVID-19 pandemic, some people have been infected but without symptoms. A new study published in the journal Nature suggests that a common genetic variation may be responsible for asymptomatic infection with the SARS-CoV-2 coronavirus.

The study, coordinated in the US by the University of North Carolina, focused on a group of genes called human leukocyte antigens (HLA), a fundamental group for the immune response that varies greatly from one person to another, EFE and Agerpres agencies reported on Wednesday.

These genes code for proteins that are used by the immune system to identify healthy cells and differentiate them from those infected by bacteria and viruses.

People with the HLA-B*15:01 genetic variant, which exists in about 10% of the population, had a higher chance of remaining asymptomatic after infection with the SARS-CoV-2 coronavirus.

The research team’s hypothesis is that the immune system of these people may respond “so quickly and strongly that the virus is destroyed before it causes any symptoms.”

The study analyzed cells from people with HLA-B*15:01 who donated blood years before the pandemic, and the results showed that they had memory T lymphocytes (which play a role in finding and destroying an infected cell) against a specific particle of the coronavirus SARS – CoV-2. This immune memory would cause a much faster response and explain why these people remained asymptomatic.

How is it possible to develop such an immune memory?

But the question they sought to answer is how it was possible to develop this immune memory against SARS-CoV-2 without being previously exposed to the virus. Thus, the authors of the study reported that there are other types of coronaviruses that have been causing seasonal colds for decades, so infection with them has already occurred. Thus, people who have the genetic variant HLA-B*15:01 seem to be able to kill SARS-CoV-2-infected cells more quickly, thanks to a cross-reactive immune response.

After analyzing the genomic sequence of all coronaviruses, the study showed that the corresponding particle of SARS-CoV-2, recognized by HLA-B*15:01, is very similar to viral particles of previous coronaviruses. Thus, these asymptomatic individuals had developed immune memory to previous coronaviruses, and due to the high similarity of this viral particle, their memory T cells were also able to recognize and kill SARS-CoV-2 more quickly.