Children tend to have mild forms of COVID-19, what is
known about the specificity and affinity of their SARS-CoV-2 antibody
response?
It is not clear which molecular mechanisms underlie the milder symptoms
of COVID-19 in children as compared to adults. Children may mount a
SARS-CoV-2 antibody response characterized by more efficient production
of the so-called natural antibodies, which arise from activated IgM+
memory B cells.38 These cells, which are more
prevalent in children than in adults, presumably produce broadly
neutralizing antibodies early during the infection. Young children also
frequently carry other respiratory viruses, which potentially limit
SARS-CoV-2 infection, as reported for other viral
infections.39 Differences between children and adults
in the regulation of ACE2 expression may also play a
role.38 ACE2 mRNA expression was high in type I and II
alveolar epithelial cells, in nasal and oral mucosa and nasopharynx, in
smooth muscle cells and endothelium of vessels from the stomach, small
intestine, colon, and in the kidney of human adults (mean age
52±22).40 Interestingly, a recent study demonstrated
age-dependent ACE2 gene expression in the nasal epithelium, which was
lowest in younger children and increased with age.41In addition, CD147, CD26 and their molecular interaction proteins seem
to be differently expressed in peripheral blood mononuclear cells and T
cells in children in comparison with adults.14