Systemic small vessel vasculitis is associated with antineutrophil cytoplasm antibodies (ANCAs). While there is mounting in vitro evidence to suggest that ANCAs are capable of enhancing leukocyte-endothelial interactions, no in vivo evidence for this has been provided. In this study a novel rat model of ANCA-associated experimental autoimmune vasculitis (EAV), induced by immunization with human myeloperoxidase (MPO), was used to analyze directly the potential effect of ANCAs on leukocyte-venular wall interactions in vivo as observed by intravital microscopy. These rats developed anti-MPO antibodies directed against rat leukocytes, showed pathologic evidence of small vessel vasculitis, and had enhanced leukocyte adhesion and transmigration in response to the chemokine Gro␣ ( IntroductionSystemic small vessel vasculitis (SVV) results in rapidly progressive glomerulonephritis and lung hemorrhage in humans and is usually fatal if untreated. 1 It is characterized by microvascular inflammation and necrosis in a variety of organs. The 2 organs that are most extensively injured in this manner are the kidney, through the development of pauci-immune crescentic glomerulonephritis, and the lung, with consequent alveolar hemorrhage. The association between antineutrophil cytoplasm antibodies (ANCAs) and SVV, initially described in the 1980s, 2 has attracted considerable interest over the past decade. These autoantibodies are principally directed against myeloperoxidase (MPO) and proteinase-3. 3,4 At first, ANCAs were regarded only as clinical markers of disease activity, but it is now apparent that they have direct biologic effects on neutrophils 5,6 and monocytes. 7 The binding of ANCAs to antigen expressed on the leukocyte cell surface following cytokine priming is followed by the activation of an array of intracellular signaling pathways, 8 with resultant degranulation and dysregulated apoptosis. 9 Granulocyte infiltration and fibrinoid necrosis of the vessel wall are the pathologic hallmarks of SVV. For this reason, investigative efforts have focused on the influence that ANCAs have on the interaction between leukocytes and the vascular endothelium, specifically with reference to the inflammatory cascade of leukocyte rolling, adhesion, and transmigration. In this context, in vitro studies using flow chamber models have shown that ANCAs can cause rolling neutrophils to arrest on platelet monolayers 10 and to promote firm adhesion and migration of rolling neutrophils on endothelial cells. 11,12 Despite growing in vitro evidence implicating ANCAs as an inducer of leukocyte-endothelial cell interactions, there has been no evidence to date demonstrating such an effect of these antibodies in vivo. The ability of ANCAs to induce systemic small vessel vasculitis and crescentic glomerulonephritis, however, has been demonstrated by transfer of anti-MPO antibodies in a mouse model of vasculitis. 13 Crescent formation in these animals occurred secondary to fibrinoid necrosis of the glomerular tuft, which was induced by necrosis and...

We report for the first time that primary human neutrophils can undergo persistent, directionally biased movement away from a chemokine in vitro and in vivo, termed chemorepulsion or fugetaxis. Robust neutrophil chemorepulsion in microfluidic gradients of interleukin-8 (IL-8; CXC chemokine ligand 8) was dependent on the absolute concentration of chemokine, CXC chemokine receptor 2 (CXCR2), and was associated with polarization of cytoskeletal elements and signaling molecules involved in chemotaxis and leading edge formation. Like chemoattraction, chemorepulsion was pertussis toxin-sensitive and dependent on phosphoinositide-3 kinase, RhoGTPases, and associated proteins. Perturbation of neutrophil intracytoplasmic cyclic adenosine monophosphate concentrations and the activity of protein kinase C isoforms modulated directional bias and persistence of motility and could convert a chemorepellent to a chemoattractant response. Neutrophil chemorepulsion to an IL-8 ortholog was also demonstrated and quantified in a rat model of inflammation. The finding that neutrophils undergo chemorepulsion in response to continuous chemokine gradients expands the paradigm by which neutrophil migration is understood and may reveal a novel approach to our understanding of the homeostatic regulation of inflammation.

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