Previous infection with another virus, cytomegalovirus, but also the genetic diversity of human populations play a role in variable immune responses to Covid-19, according to a study recently published in the journal Nature and taken over by Agerpres.
French scientists (Institut Pasteur, CNRS, Collège de France), supported by international researchers, studied variations in immune responses to SARS-CoV-2 depending on origin.
They exposed to the virus immune blood cells obtained from 222 healthy donors from Central Africa, Western Europe and East Asia, writes AFP.
By sequencing RNA from individual cells, they analyzed the SARS-CoV-2 responses of 22 blood cell types and combined these results with serological and genetic information on the same individuals.
As a result, scientists have identified about 900 genes that behave differently in different populations. According to them, these variations are mainly due to the cellular composition of the blood.
One of the factors influencing these cellular differences is exposure to cytomegalovirus (a generally harmless infection in the herpes family). 99% of the Central African population is cytomegalovirus seropositive, compared with 50% of the East Asian population and 32% of Europeans.
Therefore, latent cytomegalovirus infection could increase the risk of severe Covid.
Genetic uniqueness also plays a role: it controls the expression of about 1,200 genes in response to Covid, according to the study.
Thus, “natural selection has influenced the current immune responses to SARS-CoV-2, especially in people of East Asian origin, where coronaviruses caused a selection about 25,000 years ago”, according to Maxime Rotival (Pasteur), co-lead author with Lluis Quintana-Murci.
The study also establishes a link between an element of prehistoric heritage and immune disparities. Between 1.5 and 2% of the genes of Europeans and Asians come from Neanderthals.
By comparing some of their results with the Neanderthal genome, the scientists discovered dozens of genes that affect antiviral mechanisms and are the result of ancient interbreeding between Neanderthals and Homo sapiens.
This work is a new illustration of the contribution that genetics can make to understanding the pandemic. Also, in mid-July, a study published in Nature showed that people who carry a certain genetic variant are twice as likely not to get sick when they contract Covid-19.
Paleogenetics also confirms its interest. In 2020, two years before receiving the Nobel Prize for Medicine, the Swede Svante Pääbo, together with other researchers, identified the presence of a certain portion of DNA, inherited from Neanderthal man, in the most seriously ill patients with Covid.
This stretch of DNA is more common in South Asian populations.
2023-08-13 21:09:40
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