Is macrophages heterogeneity important in determining COVID-19 lethality?

COVID-19 (coronavirus disease 2019) pandemic due to infection with SARS-CoV-2 has led to the death of thousands of adults worldwide. It is now clear that the hyper-inflammatory response triggered by SARS-CoV-2 plays a major role in disease severity and lethality of the infection. Macrophages are innate immune cells that sense and respond to infections by producing a plethora of inflammatory molecules and by interacting with other inflammatory cells. Therefore, macrophages may be diriment on eliminating pathogens and promoting organ repair. However, macrophages can be a major player of the so called cytokine storm and may be damaging to the tissues. It is believed that macrophage activation syndrome is induced by SARS-CoV to be lethal. Surprisingly and fortunately few children die from COVID-19. For instance, in Italy, out of more than 30.000 deaths for COVID-19, three are children. Therefore, we must wonder why? Are macrophages different in children compared to adults? In my opinion they are different. It has been demonstrated that macrophages populate the lung in three “developmental waves”, and it has been suggested that similar waves may be observed in other important organs, such as the heart and kidney. It is most likely that macrophages heterogeneity is involved in determining the severity. There are no doubts that macrophages are important in determining life or death in these patients. Comparing macrophages of children with those of adults with different degrees of disease severity is, therefore, mandatory.