Why is someone "asymptomatic" after being infected with COVID-19? The latest 30000 person study reveals the cause COVID-19 | cells | symptoms
Since the outbreak of COVID-19, scientists have been puzzled by a problem, that is, why some people remain asymptomatic after infection with New Corona, while others' symptoms persist for a long time, which is considered to be suffering from "New Corona".
The latest study published in the journal Nature on July 19th uncovered the "tip of the iceberg" of asymptomatic infections. The study found that if the gene of some immune system molecules on the surface of a cell called HLA mutates, it is more likely to cause no symptoms after infection with COVID-19.
The study found that about 20% of COVID-19 infected people had no symptoms after detecting COVID-19 positive.
This study included nearly 30000 participants. The researchers tested the association between five HLA genotypes and the course of COVID-19 disease, and found that a HLA-B * 15:01 genotype was most closely associated with asymptomatic infection. People carrying these genetic mutations are eight times more likely to remain asymptomatic after infection than those who do not carry these mutations.
"This genetic association is due to pre-existing T cell immunity. We found that T cells from individual samples carrying HLA-B * 15:01 had an immune response to peptides derived from other respiratory coronavirus with immune dominance before the COVID-19 epidemic, so that they could also have cross immunity to COVID-19," the researchers said.
T cells are immune cells that help the body recognize and remember proteins. They establish memories for the immune system so that they can react and produce antibodies when pathogens are seen again.
HLA can be classified into type 1 and type 2. Type 1 is further divided into HLA-A, HLA-B, and HLA-C; Type 2 is further divided into HLA-DP, HLA-DQ, and HLA-DR, among which there are tens of thousands of variants. "There are over 50000 subtypes of HLA in the population, and HLA is the most polymorphic gene in the population," a viral immunology expert told a reporter from First Financial News.
According to the data cited by the aforementioned experts from their institution, HLA-B * 15:01 accounts for approximately 2% of the Chinese population. "In fact, HLA is related to many autoimmune diseases, and similar reports have been published, but this time it is related to COVID-19, so it has its value," he told China Business News.
HLA molecules extend from the surface of certain human white blood cells and many other tissues in the body, delivering protein fragments to the immune system, so that when the immune system encounters the virus again, it can recognize them.
Gil Horenbach, the author of the study and professor of neuroscience at the Weill Institute of Neuroscience at the University of California, San Francisco, said that after the cells were infected with COVID-19, the viral proteins were translated in the cells, and some protein fragments would be delivered to the cell surface, and HLA molecules would seize them and retain them, so that T cells could see them.
Although there is a strong association between the HLA-B * 15:01 genotype and asymptomatic infections, researchers indicate that this still accounts for only 20% of asymptomatic infections, so it is not the only explanation for people experiencing asymptomatic infections.
"Undoubtedly, there must be other important genetic and non genetic factors that can prevent certain individuals from developing symptoms after infection, but we still don't know what these factors are," said Holenbach.
Similarly, genetic changes may also be part of the risk of long-term infection with COVID-19. Another recently published preprint study that has not yet been peer reviewed shows that individuals are more likely to suffer from long-term COVID-19 when the gene of FOXP4, an active protein in the lung and immune system, has some changes.
The study found that people with FOXP4 gene mutation are about 60% more likely to have new crowns than those without the gene mutation. This discovery provides research clues for the potential mechanism of the new crown.
