ACE2 and COVID-19: As anticipated, surface expression of ACE2 was barely detected (0.8% ± 0.1%; means ± SEM) in any of the untreated myeloid cells; however, R848 treatment dramatically enhanced surface expression of ACE2 in myeloid subsets from COVID-19 patients and healthy controls, especially in CD14+ classic monocytes (11.0% ± 2.7%) and CD68+ macrophages (19.3% ± 1.8%) (Fig. 6a, b), which was consistent with our flow cytometry data that showed increased surface ACE2 upon TLR7/8 activation in CD14+ monocytes from healthy controls (Fig. 1c, d).