An increased plasma concentration of von Willebrand factor (vWF) is detected in individuals with many infectious
diseases and is accepted as a marker of endothelium activation and prothrombotic condition. To determine
whether ExoU, a Pseudomonas aeruginosa
cytotoxin with proinflammatory activity, enhances the release of vWF,
microvascular endothelial cells were infected with the ExoU-producing PA103 P. aeruginosa
strain or an exoU-deficient
mutant. Significantly increased vWF concentrations were detected in conditioned medium and subendothelial
extracellular matrix from cultures infected with the wild-type bacteria, as determined by enzyme-linked immunoassays.
PA103-infected cells also released higher concentrations of procoagulant microparticles containing increased
amounts of membrane-associated vWF, as determined by flow cytometric analyses of cell culture supernatants. Both
flow cytometry and confocal microscopy showed that increased amounts of vWF were associated with cytoplasmic
membranes from cells infected with the ExoU-producing bacteria. PA103-infected cultures exposed to platelet suspensions
exhibited increased percentages of cells with platelet adhesion. Because no modulation of the vWF mRNA
levels was detected by reverse transcription-polymerase chain reaction assays in PA103-infected cells, ExoU is
likely to have induced the release of vWF from cytoplasmic stores rather than vWF gene transcription. Such release
is likely to modify the thromboresistance of microvascular endothelial cells.