MPO and granulomatosis with polyangiitis: These studies have shown that the autoantigen specificities PR3 and MPO correlate better with different HLA risk genes (PR3-ANCA with HLA-DP, MPO-ANCA with HLA-DQ) than with the clinical and pathological phenotypes of GPA and MPA.15 Moreover, the association with the genes encoding PR3 (PTN3) and its inhibitor α-1-antitrypsin (SERPINA1) with PR3-ANCA disease and/or GPA additionally supports a central pathogenetic role of these autoantigens and their neutralizing counterparts.15