[Pathophysiology of ANCA-associated vasculitides]

ANCA-associated vasculitides comprise granulomatosis with polyangiitis (GPA) (formerly names Wegener's granulomatosis), Churg-Strauss syndrome (SCS) (which will be renamed GPA and eosinophilia) and microscopic polyangiitis (MPA). Immune cells (dendritic and non dendritic cells) and inflammatory cells (neutrophils, monocytes, macrophages) and resident cells (endothelial cells, fibroblasts) are implicated in the pathophysiology of ANCA-associated vasculitides. One of the targets of ANCA, myeloperoxydase, is only present in the azurophil granules of neutrophils, whereas the other target of these antibodies, proteinase 3, is also present at the internal face of cytoplasmic membrane of neutrophils, as well as at their surface. Anti-myeloperoxydase ANCA are pathogenicin vitroandin vivo, whereas the pathogenicity of anti-proteinase 3 ANCA has only been demonstrated in vitro and recent studies suggest a pathogenic role of ANCA anti-PR3 in mouse model. Two phenotypes of GPA can be distinguished: a granulomatous form, localized to the respiratory tract with Th1 immune response features, and a vasculitic form with Th2 immune response features. Recently, an increase in TH17 lymphocytes at the acute phase and a defect in T regulatory cells at the chronic phase have been identified in GPA. The role of B-lymphocytes in the pathogenesis of ANCA-associated vasculitides is now well documented by the effectiveness of rituximab in the treatment of this condition.