Histological image of chronic stage AIP. (A), (C), (D) Characteristics of ordinary CP. Mild inflammatory cell invasion, acinar atrophy, and slight IgG4-positive plasma cell infiltration are present in intralobular areas. Thick fibrosis is observed in interlobular areas. (B), (E), (F) Characteristics of AIP. Dense plasma cell and lymphocyte invasion, storiform fibrosis, obliterative phlebitis, and abundant IgG4-positive plasma cell infiltration exist in intralobular areas. Opaque fibrosis is present in interlobular areas. Hematoxylin and eosin staining, low-power field (×40) (A, B), hematoxylin and eosin staining, high-power field (×400) (C, E), and IgG4 immunostaining, high-power field (×400) (D, F) images.