MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: Tao Su et al reported a case of typical IgG4-TIN concurrent with IgG4 MPO-ANCA-positive necrotizing crescentic GN.[21] Raissian et al reported that moderate to marked IgG4-positive plasma cell infiltration is observed in 31.7% of patients with pauci-immune vasculitis,[9] especially in MPO-ANCA-associated EGPA or Churg–Strauss syndrome.[7] Moreover, ANCA is sometimes absent in AAV cases.