MMP9 and acute respiratory distress syndrome: Notably, Neutrophils_FGL2 was significantly less abundant in ARDS patients, Neutrophils_RPL23A, Neutrophils_MMP9, and Neutrophils_NAIP were more abundant in sep-ARDS patients, while Neutrophils_MS4A3 and Neutrophils_LTF were more abundant in the PNE-ARDS patient (Figure 3C), thus tentatively demonstrating the heterogeneity of neutrophil subpopulations among patients.