Eculizumab, a humanized monoclonal antibody that blocks the activation of terminal complement at C5 and prevents the formation of C5a and MAC, was effective in patients with paroxysmal nocturnal hemoglobinuria.[28] An orally active small molecule that blocks C5a receptor 1 was also successful in sparing concomitant corticosteroids in Phase II studies of AAV patients.[29] Various other complement-based therapies including C3-, factor B-, and factor D-targeted agents have been developed for many types of diseases. Here, C5 is linked to paroxysmal nocturnal hemoglobinuria.