SPP1 and COVID-19: Analysis of SPP1 and S100A12 expression in other cell types present in lung tissue (Figure 1I and Supplemental Figure 2) demonstrated that BALF macrophage populations are the main cells expressing SPP1 and S100A12 in severe COVID-19, and due to their high numbers in BALF of severe COVID-19(Supplemental Figure 1), FCN+ and FCN+SPP1+ macrophage clusters are likely the main contributors to the S100A12 and SPP1 pool in the COVID lung.