Why Children May Experience Mild COVID-19

Compared to adults, children with COVID-19 have a lower T cell response, possibly leading to mild or asymptomatic infections.

AsianScientist (Sep. 8, 2021) – Among the plethora of defense mechanisms activated against COVID-19, immune cells called T cells may underlie the milder symptoms that children experience compared to adults. Researchers from Hong Kong found a dampened T cell response in children, publishing in Nature Communications.

When SARS-CoV-2, the virus that causes COVID-19, infiltrates the body, our immune defenses kick into action, recruiting an army of immune cells. The type and amount of immune cells recruited influence the severity of disease and build up protective mechanisms against future reinfections.

While most COVID-19 patients show little to no symptoms, children especially tend to have less severe clinical reactions than adults do. Struck by these differences, scientists investigated various molecules like the amount of viral particles in the blood and the virus-neutralizing antibodies, produced by another class of immune cells known as B cells.

However, these past efforts could not pinpoint the immune mechanisms behind the varying levels of severity. As it turned out, the difference-makers were the lower CD4+ and CD8+ T cells in children, discovered researchers led by Dr. Sophie Valkenburg from the University of Hong Kong.

To evaluate the immune response, the team stained and quantified the diversity of cells present in patient samples taken from adults and children who had mild or asymptomatic infections. Their analysis revealed that CD4+ T cells act quickly and the response strengthens with age, while CD8+ T cell response takes time to build up after infection and may compensate for inadequate antibody responses.

While B cells use antibodies to do the attacking, some T cells like CD8+ take on a more direct strategy, spurring cell death by targeting specific proteins carried by virus-infected cells. Others like CD4+ aid B cells’ transformation into antibody-producing cells and help the body remember the viral targets.

Given their critical role in long-term protection, children’s lower CD4+ levels might suggest a weaker long-term response and may affect disease severity if reinfected, the researchers noted.

Moreover, the reduced T cell activation may be driven by the inherently lower immunity of children at the baseline. Since their bodies have likely been less exposed to other coronaviruses such as those causing the seasonal flu, children’s immune systems have not yet learned to respond to these infective agents, leading to mild effects.

With the pandemic raging on, such findings continue to uncover new insights into children and adults’ differing protective strategies against SARS-CoV-2, and more studies will only help paint a fuller picture of immune cells’ roles in fighting COVID-19.

“A coordinated cellular immune response has been key to the clinical resolution of SARS-CoV-2 infection,” the authors wrote. “Children have reduced SARS-CoV-2 T cell responses due to lower baseline immune activation, and further research is still needed to discern the protective role of T cells in COVID-19.”

The article can be found at: Cohen et al. (2021) SARS-CoV-2 Specific T Cell Responses Are Lower in Children and Increase With Age and Time After Infection.


Source: The University of Hong Kong; Photo: Shutterstock.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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