S100A8 and COVID-19: We also measured the epithelial cell–derived biomarkers S100A8, regenerating islet-derived protein 3 alpha (REG3A), and IL-1α (Supplemental Figure 13 and Supplemental Table 3) and found both S100A8 and REG3A levels to be modestly increased in COVID-19 patients relative to HVs across all severity categories.