Previous studies suggested that monocytes upregulate major histocompatibility complex (MHC) II cell surface receptor human leukocyte antigen receptor (HLA-DR) molecules in granulomatosis with polyangiitis (GPA) patients with proteinase 3 (PR3-) and myeloperoxidase (MPO-) ANCA seropositivity [14]. Here, MPO is linked to granulomatosis with polyangiitis.