Neutrophil depletion reduces edema formation and tissue loss following traumatic brain injury in mice

Background: Brain edema as a result of secondary injury following traumatic brain injury (TBI) is a major clinical concern. Neutrophils are known to cause increased vascular permeability leading to edema formation in peripheral tissue, but their role in the pathology following TBI remains unclear. Methods: In this study we used controlled cortical impact (CCI) as a model for TBI and investigated the role of neutrophils in the response to injury. The outcome of mice that were depleted of neutrophils using an anti-Gr-1 antibody was compared to that in mice with intact neutrophil count. The effect of neutrophil depletion on blood-brain barrier function was assessed by Evan's blue dye extravasation, and analysis of brain water content was used as a measurement of brain edema formation (24 and 48 hours after CCI). Lesion volume was measured 7 and 14 days after CCI. Immunohistochemistry was used to assess cell death, using a marker for cleaved caspase-3 at 24 hours after injury, and microglial/macrophage activation 7 days after CCI. Data were analyzed using Mann-Whitney test for non-parametric data. Results: Neutrophil depletion did not significantly affect Evan's blue extravasation at any time-point after CCI. However, neutrophil-depleted mice exhibited a decreased water content both at 24 and 48 hours after CCI indicating reduced edema formation. Furthermore, brain tissue loss was attenuated in neutropenic mice at 7 and 14 days after injury. Additionally, these mice had a significantly reduced number of activated microglia/macrophages 7 days after CCI, and of cleaved caspase-3 positive cells 24 h after injury. Conclusion: Our results suggest that neutrophils are involved in the edema formation, but not the extravasation of large proteins, as well as contributing to cell death and tissue loss following TBI in mice

Myelomonocytic cell recruitment causes fatal CNS vascular injury during acute viral meningitis.

Lymphocytic choriomeningitis virus infection of the mouse central nervous system (CNS) elicits fatal immunopathology through blood-brain barrier breakdown and convulsive seizures. Although lymphocytic-choriomeningitis-virus-specific cytotoxic T lymphocytes (CTLs) are essential for disease, their mechanism of action is not known. To gain insights into disease pathogenesis, we observed the dynamics of immune cells in the meninges by two-photon microscopy. Here we report visualization of motile CTLs and massive secondary recruitment of pathogenic monocytes and neutrophils that were required for vascular leakage and acute lethality. CTLs expressed multiple chemoattractants capable of recruiting myelomonocytic cells. We conclude that a CD8(+) T-cell-dependent disorder can proceed in the absence of direct T-cell effector mechanisms and rely instead on CTL-recruited myelomonocytic cells

Heparin-binding protein (HBP/CAP37): A missing link in neutrophil-evoked alteration of vascular permeability

Polymorphonuclear leukocyte infiltration into tissues in host defense and inflammatory diseasecauses increased vascular permeability and edema formation through unknown mechanisms.Here, we report the involvement of a paracrine mechanism in neutrophil-evoked alteration inendothelial barrier function. We show that upon neutrophil adhesion to the endothelial lining,leukocytic 2 integrin signaling triggers the release of neutrophil-borne heparin-binding protein(HBP), also known as CAP37/azurocidin, a member of the serprocidin family of neutrophilcationic proteins. HBP induced Ca++-dependent cytoskeletal rearrangement and intercellular gapformation in endothelial-cell monolayers in vitro, and increased macromolecular efflux in microvesselsin vivo. Moreover, selective inactivation of HBP prevented the neutrophils from inducingendothelial hyperpermeability. Our data suggest a fundamental role of neutrophil-derivedHBP in the vascular response to neutrophil trafficking in inflammation. Targeting this moleculein inflammatory disease conditions offers a new strategy for prevention of endothelial barrierdysfunction caused by misdirected leukocyte activation