Serum C3a, C5a, soluble C5b-9, and Bb fraction correlate with disease activity in MPO-ANCA positive renal vasculitis (14). Avacopan (C5aR antagonist) is being explored as a potential therapeutic target, but specific data on EGPA are lacking (15). Here, C3 is linked to eosinophilic granulomatosis with polyangiitis.