S100A9 and COVID-19: At 200 ng/mL, SPP1 strongly increased the expression of alarmins (S100A12, S100A9), IL-1β, and chemokines (CXCL8, CCL2-4) with a commensurate reduction of MHCII and antiinflammatory ENTPD1 (encoding CD39; Figure 6G), which resembles the proinflammatory changes in the blood CD14+ monocyte subset in severe COVID-19 (22, 23).