Children seem to be protected from this happening because of the stronger basic activation of MDA5 and similar receptors. In fact, Binder’s experiments showed that, in children, SARS-CoV-2 is simply too slow to prevent the cells from producing interferons. In cell cultures of lung epithelial cells, Binder tested whether the larger numbers of MDA5s, as observed in children, might preserve the interferon reaction. Adults have very few of these receptors-the molecules have to be produced from scratch in the event of an infection. This costs time, which SARS-CoV-2 uses to stifle the entire immune signaling system. “SARS-CoV-2 multiplies very quickly in cells, and this means that the virus proteins are also formed very quickly,” says Binder, who researches interferons. “And they suppress the interferon system so dramatically that we see only minimal or no interferon production in cell cultures when there is an infection.” Interferon’s Dual Roles “The interferons are extremely effective against virus infections,” explains Marco Binder of the German Cancer Research Center in Heidelberg, a co-author of the Nature Biotechnology study. As an effective countermeasure, however, the novel coronavirus has its own proteins that prevent interferons from being produced. It also directs the production of type I interferons, which are crucial to the innate, or rapid-response, immune system’s ability to fight viruses. They activate immune cells and put them in a special state of vigilance that makes it difficult for viruses to multiply. One such receeptor molecule, MDA5, is a sensor for foreign RNA found in many viruses, including SARS-CoV-2. The samples also show that the children’s cells produce larger quantities of immune receptors that recognize viruses and trigger the immune response. “The defense against viruses works on two levels. First, you get the antiviral response within the cells through receptors that, for example, induce the production of interferon,” Lehmann explains. “The second level the immune cells in the tissue, such as activated killer cells and neutrophils.” The study carried out by her group shows that these two levels of viral control are on high alert in children. The team analyzed almost 270,000 cells from swab samples taken from the nasal mucosae of people aged between four weeks and 77 years. About half of them were infected with SARS-CoV-2, the virus that causes COVID. As the team reports in Nature Biotechnology, children do not only have many more immune cells in their mucous membranes they also more quickly produce type I interferons, which are crucial for fighting viruses. As a result, these key molecules may also provide protection from the dysregulation of the immune system that occurs in many severe cases of COVID-19. The researchers examined differences in the cell types of the mucous membranes of children and adolescents. In children, this system reacts much faster to viruses that it has never encountered, such as pandemic pathogens. At least, that is what a recent study by Irina Lehmann of the Berlin Institute of Health at Charité and her colleagues suggests. In the mucous membranes of their airways, it is much more active than that of adults. The immune system uses a special mechanism to protect children from novel viruses-and it typically saves them from a severe course of COVID-19 in two different ways.
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