Fig. 2.

The difference in immune responses in the lungs of children and adults to SARS-CoV-2 is the reason for the different clinical manifestations.

In children, SARS−COV-2 infection may be quickly eradicated due to having less mature ACE2 receptors and rapid activation of immunocompetent immune cells (right side). In adults, the negative regulation of the immune response in the respiratory tract, late changes in the nature of the immune responses, decrease in population of immunocompetent cells, increase of ACE2 expression, ACE2 shedding and sACE2 production, all can lead to an uncontrolled immune response, widespread ineffective inflammation, immune dysregulation, cytokine storm and ARDS (left side). ACE2: Angiotensin−COnverting enzyme 2; SARS−COV2: severe acute respiratory syndrome coronavirus 2; ARDS: Acute respiratory distress syndrome.