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