MMP12 and COVID-19: In 39 critically ill patients with COVID-19, the median AAT level was modestly increased (by 1.5-fold the upper limits of normal), but there was a disproportionately increase in blood matrix metalloproteinase-12 (MMP-12, produced mainly by macrophages) and neutrophil elastase by ≥10-fold and four- to seven-fold, respectively [124].