Since the SARS-CoV-2 pandemic began, it has been observed that children rarely experienced severe symptoms of COVID-19, and this continued as the coronavirus developed different mutations, including worrying ones such as delta or omicron. Now, a new study has found key differences in the immune response of adults and children that may help explain why children are at less risk of severe COVID-19.
In the research, which has been carried out by scientists from the Wellcome Sanger Institute, University College London and their collaborators and has been published in Nature, SARS-CoV-2 infection in adults and children in different organs has been compared. The results show that a more powerful ‘innate’ immune response, characterized by rapid deployment of interferons, was produced in the children’s airways and helped to reduce viral replication in the first place. The slower immune response in adults, however, allowed the virus to more easily invade other parts of the body where the infection was more difficult to control.
Differences in the immune system of children and adults
Children’s ‘innate’ immune systems have a greater ability to automatically recognize dangerous viruses or bacteria, activating B and T cells that can adapt to the threat. Adults, meanwhile, have a more “adaptive” immune system that includes a large repertoire of “memory” B and T cell types, which have been previously trained by exposure to pathogens to respond to a particular threat . Although this adult immune system also has an innate response, it is more active in children.
“Children’s innate immune system is more flexible and better able to respond to new threats”
In both cases, there is a group of proteins with potent antiviral activity called interferons that are released in the presence of viruses or bacteria and signal nearby cells to strengthen their defenses. The production of these proteins contributes to the activation of B and T cells, which are responsible for eliminating infected cells and preventing the pathogen from spreading further.
To carry out the research, its authors obtained and processed blood and respiratory tract samples from 19 pediatric and 18 adult patients with COVID-19, who ranged from asymptomatic individuals to others with severe symptoms, and also included in the study analyzes samples from a control group made up of 41 healthy patients (children and adults).
Single-cell sequencing of the samples revealed that interferons were more strongly expressed in healthy children compared to adults, with a more rapid immune response to respiratory tract infections in children. This would help limit the replication of the virus from the start and give minors an advantage in preventing the coronavirus from infecting the blood and other organs.
The researchers also verified how the immune system of adults, due to its high number of “killer” immune cells such as B and T cells, can act against the patient’s body once SARS-CoV-2 has spread throughout the body. other areas of your body.
Identify patients at higher risk of severe COVID
“Because SARS-CoV-2 is a new virus, it is not something that the adaptive immune system of adults has learned to respond to. Children’s innate immune systems are more flexible and better able to respond to new threats. What we saw at the molecular level is high levels of interferons and a very rapid immune response in children that helps explain why they are less affected by COVID-19 than adults,” said Masahiro Yoshida, MD, from University College. London.
“Some of the differences we see between children and adults can help us think about how we assess personal risk for adults as a way to mitigate serious illness and death.”
“Compared to children, adult blood has a greater number and variety of cytotoxic immune cells, which are designed to kill infected cells to prevent the spread of an infection. But there is a fine line between helping and hindering. Once the virus has spread to various areas of the body, organ damage can be caused by the immune system trying and failing to control the infection. Our study shows that not only do children respond better initially, but if the virus enters the blood, the cytotoxic response is less forceful”, says Dr. Marko Nikolić, also from University College London.
“Simply put, the innate immune response is better at fighting COVID-19 and children have stronger innate immunity, but immunity is also a complex ballet involving many cell types. The timing and types of cells that are activated will influence how an infection develops, and this will vary between people for all sorts of reasons besides age. Some of the differences we see between children and adults may help us think about how we assess personal risk for adults as a way of mitigating serious illness and death,” concludes Dr Kerstin Meyer, from the Wellcome Sanger Institute.
The findings will help predict the risk of severe disease in those infected with SARS-CoV-2, as a nasal swab could be used to measure the immune response in newly infected adults and thus identify those most at risk and those at risk. preventive treatment with monoclonal antibodies or inhalation of interferons could be given to them, which, as recent studies have suggested, could be an appropriate therapy in these cases.
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