CD4 and COVID-19: In addition, concerning cell populations, elevated levels of immature monocytes, megakaryocytes, and B cells, and decreased levels of dendritic cells (mainly CD1+ conventional dendritic cells) and T cells (especially CD3+, CD4+ and CD8+ T cells) are mainly observed in severe COVID-19 patients and as a result could be considered as markers of severe disease [7,39,40,49,50,53,54,56,67,69].