Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a prototypic autoimmune disease, with a subset of AAV patients manifesting anti-myeloperoxidase (MPO) IgG. Patients with AAV respond positively to B cell-targeting and complement-targeting therapies, but disease flares are not uncommon. Here, by comparing samples from healthy individuals and MPO