CXCR4 and COVID-19: In mild COVID-19 disease course, studies have reported an increase in HLA-DRhiCD11chi inflammatory monocytes with an interferon-stimulated gene signature, indicative of terminally differentiated monocytes, whereas severe COVID-19 was characterized by a lack of type I IFNs, high levels of HLA-DRlow classical monocytes and CD10lowCD101-CXCR4+/- neutrophils with an immunosuppressive profile in blood and lungs of severe cases, suggestive of emergency myelopoiesis (7, 47–50).