CCL2 and acute respiratory distress syndrome: As a main ligand for CCR2, CCL2 has been detected in BALF of ARDS patients and verified as a pivotal chemokine involved in regulating neutrophil migration (Williams et al., 2017).This suggests a possible involvement of CCL2/CCR2 axis in macrophage activation and accumulation, which was supported by an inhibitory effect of CCR2 down-regulation on LPS-induced macrophage chemotaxis toward CCL2.