GPA is a member of the anti-neutrophil cytoplasmic antibody (ANCA) vasculitides. Given the strong association of GPA with ANCA production, much focus has been placed on understanding the mechanisms of ANCA production and pathogenesis. The factors by which ANCAs are initially generated are poorly understood. The majority of in vitro and animal model research implicating neutrophils and T cells as the principal inflammatory cells in GPA is surprising given the known impressive clinical treatment response to B cell depletion with rituximab. This discordance reinforces that the knowledge gap between pathogenesis and therapy is GPA is wide.