Study examines child immune response in COVID-19

Children and adults exhibit distinct immune system responses to infection by the virus that causes the novel coronavirus (COVID-19), which may explain why outcomes tend to be much worse in adults, according to new research by Yale University and Albert Einstein College of Medicine published in the journal Science Translational Medicine.

A widespread and dangerous immune response to the virus has been linked to acute respiratory distress syndrome, the need for ventilation, and increased mortality in adults with COVID-19. These outcomes are less common in children, which has led to speculation that immune system response to the virus is somehow suppressed.

The study examined serum and cell samples obtained from pediatric and adult patients diagnosed with COVID-19. The researchers looked for variations in the types of immune system responses in patients who experienced different health outcomes from the novel coronavirus. The subjects also included children and adolescents diagnosed with multi-system inflammatory syndrome (MIS-C), a rare complication of COVID-19 infection in young people that is associated with a variety of severe health complications.

The researchers found that children expressed higher levels of two specific immune system molecules. The researchers said they believe this may contribute to the better outcomes. The analysis also showed that certain types of antibody responses thought to be protective were higher in adults, including those with severe cases, than in children, the study said.  

Specifically, the researchers found that levels of two immune system molecules, interleukin 17A (IL-17A), which helps mobilize immune system response during early infection, and interferon gamma (INF- γ), which combats viral replication -- were strongly linked to the age of the patients. The younger the patient, the higher the levels of IL-17A and INF- γ, according to the study.

The two molecules are part of the innate immune system, a more primitive, non-specific type of response activated early after infection, the researchers. Conversely, the adults showed a more vigorous adaptive immune system response including higher neutralizing antibody levels, which record signatures of pathogens and target them for elimination.

Additionally, the researchers found that children with rare cases of MIS-C also have high levels of IL-17A and INF- γ, but seldom exhibit severe damage to lung tissue that characterizes severe adult cases. These children, however, share other immune response signatures linked to more severe adult cases. The source of the IL-17A and INF- γ molecules remain unknown, but its identification may shed light on cells that can be targeted to prevent severe effects from COVID-19.

Boosting certain types of immune responses, they said, may be beneficial to patients.

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