PSMB9 and COVID-19: When we instead investigated the relationships between these genes and the M2 macrophage marker CD163, which was overexpressed in bronchoalveolar cells from patients with severe COVID-19 (Fig. 3B and Additional file 1: Figure S2A), we found correlations that were still positive but notably weaker (between CD163 and PSMB8, coefficient r = 0.45; CD163 and PSMB9, coefficient r = 0.46; CD163 and PSMB10, coefficient r = 0.47; CD163 and CALR, coefficient r = 0.58) (Additional file 1: Figure S2B).