Page 208 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

184 Constantina Yiannakis, Lorna Ward and Matthew David Morgan

added. The importance of cytokines in the pathogenic process was shown by the fact that
these effects could be ameliorated by the addition of anti-TNF-? antibodies [81].

Prominent macrophage and neutrophil invasion was found at sites of glomerular injury
which, along with the fact that crescentic glomerulonephritis did not develop in neutrophil
depleted mice, supports the pivotal role of neutrophils in the pathogenesis of AAV [82].

Leukocyte adhesion and transmigration were shown by intravital microscopy to be
enhanced by anti-MPO IgG in wild-type mice pre-treated with cytokines. ?2-integrins
(CD18) and Fc? receptors were shown to be necessary as recruitment was not seen following
the co-administration of anti-CD18 antibodies or in Fc receptor ? chain-/- mice [83].

Kuligowki and co-workers [84] found that high-dose anti-MPO induced ß-integrin
dependent adhesion in the absence of LPS, while LPS was necessary to induce adhesion at
low doses of anti-MPO.

In Vitro Activation of Neutrophils by ANCA

In vitro experiments on the effect of patient derived IgG containing ANCA demonstrated
ANCA-activation of cytokine primed neutrophils. During the priming process, MPO and PR3
were translocated to the plasma membrane of neutrophils where they can interact with ANCA
[85-87]. In addition to increasing surface expression of ANCA, interleukin (IL)-18, TNF? and
granulocyte macrophage colony stimulating factor lead to mobilization of nicotinamide
adenine dinucleotide phosphate (NADPH) oxidase complex components necessary for
superoxide generation [87-90]. Subsequent crosslinking between ANCA and Fc? receptors
and ANCA antigens results in degranulation, production of proinflammatory cytokines,
adhesion to endothelium and generation of superoxide with multiple signaling pathways
implicated [91-96] (figure 1). Neutrophil gene expression is also induced by binding of both
intact ANCA and F (ab?) 2 portions [97].

Effect of ANCA on Neutrophil-Endothelium Adhesion

Endothelial necrosis with exposure of the basement membrane leading to platelet
aggregation, thrombosis and occlusion is a histological feature of small vessel disease in
AAV [98]. Swelling, necrosis and dehiscence of endothelial cells is seen as an early
histological feature and thought to be the mediated by ANCA activation of cytokine primed
circulating neutrophils resulting in neutrophil adhesion to and transmigration through
endothelium associated with neutrophil degranulation and release of intracellular contents and
production of superoxide. Adhesion and transmigration of leukocytes is promoted by the
release of chemoattractant proteins by endothelial cells and upregulation of adhesion
molecules. The serum concentrations of soluble factors associated with this process include
vascular endothelial growth factor (VEGF), inter-cellular adhesion molecule (ICAM)-3, P-
selectin, thrombomodulin, angiopoietin-2, matrix metalloproteases 1, 3, and 9; endothelial
microparticles and stem cells [99-105].

In vitro studies showed that ANCA stabilized adhesion and promoted transmigration of
neutrophils flowing over endothelial cells [106]. This interaction depended on the interaction
between neutrophil-expressed CXCR1 and CXCR2, and CD18/CD11b and their ligands on

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