Immune Responses of Children vs. Adults

Children and Adults: COVID-19 Immune Response

    The coronavirus has spread rapidly around the globe and has infected millions of childrens and adults around the world. Unlike other viral infections such as the flu, multiple studies have found that COVID-19 has more serious effects on adults than on children. Adults and children react differently to the virus, the main difference being that children are at a lower risk of infection compared to adults (see Who's at Risk). Additionally, children are more likely to be asymptomatic or have less severe symptoms (see Are Schools Ready to Reopen) yet are found to carry a higher viral load than adults (see Children Carry More Coronavirus than Adults). A new study published on September 21 in Science Translational Medicine looks into the reason why children and adults react differently to the coronavirus through studying the COVID-19 immune responses of each group. 

The Study

    The authors of the study took clinical data from 65 children under the age of 24 and 60 adults over the age of 24. All these patients were hospitalized for COVID-19 at the Montefiore Medical Center in New York City. The hospital stay for adults averaged at 2 weeks while the average hospital stay for children was around 6 days. 

    Surprisingly, patients from the adult group showed a stronger immune response than children. The results found that adults had a more vigorous T-cell response, which kills infected cells and helps activate the immune system. Neutralizing antibody levels were also higher in adults compared to children. Neutralizing antibodies are a form of immunity that bind to viral proteins to prevent infection. Additionally, antibody-dependent cellular phagocytosis (ADCP), which is an important mechanism used to remove disease, had significantly increased activity levels in the adult group compared to the pediatric. So why are adults more likely to experience severe COVID-19 cases and longer hospital stays compared to children despite robust immune responses including higher levels of antibodies, T-cells, and ADCP?

    While children had lower levels of antibodies and T-cells compared to adults, the authors found that children had higher amounts of IL-17A, an immune signaling receptor typically associated with T-cells. However, adults had an abundance of T-cells but fewer IL-17A receptors compared to children. This led the authors to come to the conclusion that there is another unknown cell type that produces IL-17A which is prevalent in children and may contribute to immune protection.  However, further research needs to be conducted to determine the cell that produces IL-17A and its specific function. The authors do not believe that immune response is a key reason for the difference of COVID-19 effects in children and adults.

As age increases, IL-17A levels decrease

Conclusion

    To summarize, the adult group was found to have higher levels of immunity building cells and proteins compared to the pediatric group despite longer hospitalization and more severe cases of COVID-19 in adults. On the other hand, children had increased levels of an immune signaling receptor called IL-17A. The authors believe there is an unknown cell that produces this receptor in children. According to the study, "the findings demonstrate that the poor outcome in hospitalized adults with COVID-19 compared to children may not be attributable to a failure to generate adaptive immune responses."

Sources

1. Pierce, Carl A., et al. “Immune Responses to SARS-CoV-2 Infection in Hospitalized Pediatric and Adult Patients.” Science Translational Medicine, American Association for the Advancement of Science, 21 Sept. 2020, stm.sciencemag.org/content/early/2020/09/21/scitranslmed.abd5487.