Anti-neutrophil cytoplasm antibodies directed against myeloperoxidase augment leukocyte-microvascular interactions in vivo Running head: ANCA enhance microvascular responses in vivo

Systemic small vessel vasculitis is associated with anti-neutrophil cytoplasm antibodies (ANCA). Whilst there is mounting in vitro evidence to suggest that ANCA 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 immunisation with human MPO, was used to analyse directly the potential effect of ANCA on leukocyte-venular wall interactions in vivo as observed by intravital microscopy. These rats developed anti-MPO antibodies directed against rat leukocytes, showed pathological evidence of small vessel vasculitis, and had enhanced leukocyte adhesion and transmigration in response to the chemokine Groα (CXCL1). Passive transfer of immunoglobulin from rats with EAV to naïve rats conferred enhanced adhesion and transmigration responses in the recipients. Furthermore, rats with EAV and recipients of ANCA-positive immunoglobulin developed extensive microvascular injury, as manifested by mesenteric haemorrhage, in response to CXCL1. This study provides the first direct in vivo evidence for the ability of ANCA to enhance leukocyte-endothelial interactions and cause microvascular haemorrhage, thereby providing a mechanism by which ANCA could exert pathogenic effects in systemic vasculitis. For personal use only. on October 3, 2017. by guest www.bloodjournal.org From