CD38 and COVID-19: Indicative of in vivo activation, increased proportions of CD4+ and CD8+ T cells expressing CD69, CD38, CD44, or HLA-DR have been reported in COVID-19 patients (5, 116, 155–158) as has the presence of pathogenic GM-CSF+/IL-6+ and GM-CSF+/IFN+ CD4+ T cells, with those experiencing severe disease presenting with significantly increased frequencies when compared to those with mild COVID-19 (116).