ANCA-associated vasculitis (AAV) is a rare, serious and often life-threatening disease. There are three sub-types of AAV: Wegener's granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome). AAV is triggered by anti-neutrophil cytoplasmic auto-antibodies and mediated by overactivated neutrophils through the terminal C5a complement damage pathway and C5a receptor. C5a and C5aR play a central role in the pathogenesis of AAV that results in the attack and destruction of the blood vessels, typically in the kidneys, lungs and other organs. AAV often occurs as a relapsing-remitting state characterized by recurring flares and accumulating irreversible organ damage that can lead to renal failure and death. The current standard of care for AAV is associated with significant safety issues. First year mortality is approximately 11 to 18 percent. The single major cause of premature mortality is not disease related adverse events, but rather infection that is thought largely to be a consequence of steroid administration. The multiple adverse effects of courses of steroid treatment (both initial courses and those that are repeated as a consequence of relapse) are major causes of both short-term and long-term disease and death.