Eculizumab (Soliris®), a humanized anti-C5 monoclonal antibody, prevents C5 from being cleaved into C5a and C5b by C5 convertase, and is currently in trials for paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), with plans to extend its use to age-related macular degeneration, myasthenia gravis, optic neuritis, early septic organ dysfunction, and prevention of rejection of kidney transplants (Melis et al., 2015; Risitano, 2015; Horiuchi and Tsukamoto, 2016). Here, C5 is linked to optic neuritis.