Neutrophil recruitment and plasma exudation are key elements in the immune response to injury or
infection. Activated neutrophils stimulate opening of the endothelial barrier; however, the underlying mechanisms have remained largely unknown. In this study, we identified a pivotal role of the proinflammatory kallikrein-kinin system and consequent formation of
bradykinin in neutrophil-evoked vascular leak. In mouse and hamster models of acute
inflammation, inhibitors of
bradykinin generation, and signaling markedly reduced plasma exudation in response to
chemoattractant activation of neutrophils. The neutrophil-driven leak was likewise suppressed in mice deficient in either the
bradykinin B2 receptor or
factor XII (initiator of the kallikrein-kinin system). In human endothelial cell monolayers, material secreted from activated neutrophils induced cytoskeletal rearrangement, leading to paracellular gap formation in a
bradykinin-dependent manner. As a mechanistic basis, we found that a neutrophil-derived
heparin-binding protein (HBP/
azurocidin) displaced the
bradykinin precursor
high-molecular-weight kininogen from endothelial cells, thereby enabling proteolytic processing of
kininogen into
bradykinin by neutrophil and plasma
proteases. These data provide novel insight into the signaling pathway by which neutrophils open up the endothelial barrier and identify the kallikrein-kinin system as a target for therapeutic interventions in acute inflammatory reactions.-Kenne, E., Rasmuson, J., Renné, T., Vieira, M. L., Müller-Esterl, W., Herwald, H., Lindbom, L. Neutrophils engage the kallikrein-kinin system to open up the endothelial barrier in acute
inflammation.