About 20% of people who contract the coronavirus do not experience symptoms of COVID-19. A team of scientists from the US and Australia found that the absence of symptoms of COVID-19 is associated with a mutation in one of the genes responsible for the immune system. This mutation allows immune cells to recognize SARS-CoV-2 and trigger an antiviral response more quickly.
The scientists invited 30,000 bone marrow donors to participate in the study – they already knew their genetic parameters since you need to pass an HLA test to become a donor. Participants reported positive coronavirus tests and any symptoms. Of the 30,000 participants, over 1,400 reported a positive test, of which 136 were asymptomatic.
After analyzing genetic parameters, the scientists found that 10% of asymptomatic participants had a human tissue compatibility system (HLA) gene mutation. The HLA genes encode molecules that capture and bring to the cell surface peptides that characterize the contents of cells. These peptides (protein fragments) are needed for immune cells to distinguish between healthy and foreign body cells. When foreign proteins are detected, T-killers destroy infected cells.
A mutation in the HLA system gene has been associated with asymptomatic COVID-19. The HLA-B*15:01 gene doubled the likelihood that a person would remain asymptomatic after being infected with the coronavirus. Moreover, two copies of this gene increased the possibility of asymptomatic COVID-19 by 8 times. Another gene, HLA-DRB1*04:01, enhanced the effect.
The scientists investigated how the coronavirus interacts with killer T-cells from healthy HLA-B*15:01-bearing donors who have never been infected with SARS-CoV-2 and have no immunological memory of the coronavirus. T-killers reacted to a fragment of the SARS-CoV-2 spike protein as if they had encountered the coronavirus before.
This behavior of killer T cells may explain why the SARS-CoV-2 spike protein fragment is structurally similar to the spike protein fragments of seasonal coronaviruses. It helps killer T cells recognize and destroy SARS-CoV-2-infected cells faster. The HLA-B*15:01 gene allows the HLA molecule to capture viral peptides more quickly, and the similarity of the SARS-CoV-2 spike protein peptide to seasonal coronavirus peptides provides a more robust response against SARS-CoV-2.
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Reference
A common allele of HLA is associated with asymptomatic SARS-CoV-2 infection
