Emerging role of high mobility group box 1 in ANCA-associated vasculitis.

High mobility group box 1 (HMGB1) has been suggested to be involved in the pathogenesis of many autoimmune diseases. In addition to its nuclear functions, extracellular HMGB1 released from activated, injured or dying cells becomes a proinflammatory mediator via binding to various receptors on the surface of responding cells. HMGB1 interacts with various systems involved in inflammation, such as the complement system and the coagulation system. Thus, HMGB1 could amplify inflammation and enhance immune responses in pathophysiology of certain diseases. In the past years, HMGB1 has been studied in several vasculitides including antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, Kawasaki disease, Henoch-Schönlein purpura, Takayasu arteritis and giant cell arteritis. Several studies showed that circulating HMGB1 levels are higher in patients with active disease compared with healthy controls, and levels are associated with disease severity. Further studies on pathogenetic mechanisms revealed pathogenic roles of HMGB1 in some vasculitides. Here we review clinical and experimental studies dealing with the role of HMGB1 in vascular inflammation, and its relation to the manifestations and prognosis of specific vasculitides, in particular ANCA-associated vasculitis.