MMP9 and infection: Neutrophil-derived proteins such as myeloperoxidase (Mpo), neutrophil elastase (ELANE), matrix metallopeptidase 9 (Mmp9), and neutrophil gelatinase-associated lipocalin (Lcn2) were among the most accentuated proteins in our data sets (Fig. 1A), suggesting that neutrophil influx and NET formation start early during infection and precede organ damage.