Mulder et al.51 assembled a comprehensive atlas of tissue and circulating mononuclear phagocytes that revealed six monocyte populations, including one with low or negative HLA-DRB1 mRNA expression (cluster #8; CD14+/S100A8/S100A9/S100A12hi) that was mapped to subjects with severe COVID-19 in a reanalysis of the Silvin et al. data50. The gene discussed is S100A9; the disease is COVID-19.