C3 and anti-neutrophil cytoplasmic antibody-associated vasculitis: C3 was also reported to play a bridging role in autoimmune-associated vasculitides (AAV) such as ANCA-associated vasculitis and systemic lupus erythematosus (SLE): it links initiating factors (autoantibodies and immune complexes) to effector mechanisms (inflammatory cell activation and tissue injury) [136,137,205].