Since the start of the health crisis, the vast majority of children have been spared from serious forms of Covid-19. We just figured out why.
- Innate immunity is the immediate response that occurs locally, at the point of entry of a pathogenic microorganism, in any individual, even in the absence of previous contact with this microorganism.
- Adaptive immunity is a response which will take 5 to 7 days before being protective, when the pathogen is encountered for the first time (primo-infection) but will be effective more quickly when the pathogen has already been encountered (we speak of a response memory).
Why are children less prone to critical forms of Covid-19 than adults? French researchers have just identified some answers. Their workspublished in the journal Frontiers in Immunology, demonstrated in particular that the innate immune response is not the same depending on the age of the patients.
No preselection
To do this, they analyzed the nasopharyngeal samples from 226 people who came to carry out a PCR test in a “drive” screening center at the Angers University Hospital, from March 2020 to March 2021. Among these individuals, 147 were infected with SARS- CoV-2. “The originality of our work is not to have pre-selected the participants, so as not to bias the results, but also to be interested in innate immunity, and more specifically in the interferon response”, emphasizes Yves Delneste, an Inserm researcher who participated in this study.
When cells are infected with any virus, they rapidly produce type I (IFN-α/β) and type III (IFN-l) interferons (IFN), which are potent natural antiviral molecules. They are called interferons because they “interfere” with the replication of the virus and protect neighboring cells from infection. These interferons all have antiviral activity, but their modes of action are not redundant. Indeed, each induces an antiviral response of different intensity and duration and acts in a distinct but complementary on the immune response.
Analysis of the samples studied by the research team reveals that, in subjects infected with SARS-CoV-2, the expression profiles of type I interferons (IFN-α/β) and type III (IFN -l) differ with age. Thus, children under the age of 15 have an increased expression of type III interferons, molecules that are not very inflammatory and of local action, which control the virus at the level of its point of entry (in the nasopharyngeal mucosa). Conversely, adults, and in particular the elderly, preferentially express type I interferons, which are inflammatory and have a more systemic action (throughout the body).
“Controlling Infection at the Point of Entry”
“These results help to explain why children would be less prone to critical forms of Covid-19 than adults. Type III interferons, which act mainly by locally protecting the epithelium, could control the infection at the point of entry, without inducing generalized excessive inflammation, and thus avoiding a slide towards the inflammatory storm with massive cell destruction that is seen in severe forms”, emphasize Pascale Jeannin (university professor and hospital practitioner) and Dominique Couez (university professor), who directed this work.
Based on these results, the scientists will now conduct a prospective study to assess whether, in children who present with clinical signs of the disease, the characteristics of the interferon response associated with the severe forms in adults are present and whether they can help predict the course of the infection.
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