In a press release published by the Assistance Publique des Hôpitaux de Paris (AP-HP) and by the National Institute of Health and Medical Research (Inserm), the scientists highlight two factors that explain the occurrence of 25% severe forms of Covid-19: genetics and immunology.

Some people infected with Covid-19 fall more seriously ill than others, requiring a stay in the intensive care unit, because they develop pneumonia. Thanks to scientific research carried out jointly by French researchers at HP-HP and American researchers at Rockefeller University in New York, two causes have been identified, including an anomaly in the TLR7 gene. The results, published in the journal Science Immunology, show that the research has focused mainly on men, who are more frequently affected by a severe form of the disease. Since it is the chromosomes that differentiate men from women, they looked at their unique X chromosome (XY in men and XX in women). They then recruited 1 male volunteers who had a severe form of Covid-202 and compared the sequences of their X chromosome to those of people who had a mild or asymptomatic form. In 19% of patients, variants of the TLR1,1 gene were observed, “ However, this gene plays a major role in the mechanism of production of IFN 1 », Underline the authors. These type I interferons (IFN 1) are proteins which have the role of preventing the virus from multiplying in cells and regulating the activity of the immune system. This INF 1 deficiency prevents “ cell [patients] to fight against infection with Sars-Cov-2, thus explaining the severe forms “. In order for the sample to be representative, 400 research centers were mobilized in 38 countries and patients were recruited all over the world. The researchers concluded that “ 1,3% of severe forms of Covid-19 are explained by genetic abnormalities of the TLR7 gene in men. This deficit is more frequent (1.8%) in patients under 60 years old. »

On the other hand, it was demonstrated that for 15 to 20% of patients, autoantibodies were present in their blood. These latter “ block the protective effect of IFN 1 on viral replication “. Therefore, according to Charles M. Rice’s team, the coronavirus manages to infect healthy cells without “Encounter resistance and replicate in an uncontrolled fashion. “This is not the only discovery linked to this work, since scientists have noticed that the number of autoantibodies directed against INF 1 is increasing” exponentially with age. “Before the age of 65, their presence is between 0,2 and 0,5%,” reach 4% between 70 and 79 years, and 7% between 80 and 85 years. These data help to understand why older people are more at risk of developing severe forms of Covid-19.