CMV-seropositive donor PBMCs exposed to CMV antigen results in endothelial damage in cocultures that is mediated predominantly by the fractalkine-CX₃CR1 interaction. Each micrograph panel shows the resulting effects of specific neutralizing antibody blocks and controls on CMV-induced endothelial damage in PBMC-AEC cocultures at day 6. Negative control was transmigrated PBMC populations using negative control media lacking chemokines; positive control was transmigrated PBMCs using untreated coculture supernatants; isotype control was PBMCs treated with isotype control antibodies for CX₃CR1-specific and RANTES-specific neutralizing antibodies, followed by transmigration into coculture supernatants; anti-CX₃CR1 block was PBMCs treated with neutralizing antibody specific for CX₃CR1, followed by transmigration into coculture supernatants; anti-RANTES block was PBMCs treated with neutralizing antibody specific for RANTES, followed by transmigration into coculture supernatants; dual block was PBMCs treated with both neutralizing antibody specific for CX₃CR1 and neutralizing antibody specific for RANTES, followed by transmigration into coculture supernatants. Extensive endothelial damage and loss are seen in positive control, isotype control, and anti-RANTES block. In contrast, protection against endothelial damage is observed in the presence of the anti–CX₃CR1-blocked samples.