CCL2 and acute respiratory distress syndrome: The construction of the PPI network to identify 12 hub genes associated with ARDS suggested that CXCL8 (IL-8), APOE, SPP1, JUN, and CCL2 were significantly up-regulated, and GZMA, MPO, PRF1, ELANE, GZMB, SELL, and CD247 were significantly down-regulated.