CXCR4 and acute respiratory distress syndrome: SDF-1 and CXCR4 are both members of the CXC subfamily and are natural ligands and receptors of one another, forming the SDF-1/CXCR4 signaling axis, which plays an important role in various biological processes related to cell migration.[12] In CPB-associated ALI, inflammatory cell infiltration into the lung mainly comprising neutrophils is a basic pathophysiological change.