Figure 3. Histopathological and Immunohistochemical Analysis of Pancreatic Tissue. (A–C) H&E: (A) Pancreatic parenchyma with destruction of normal architecture, extended storiform fibrosis (black indication) and presence of lymphoplasmacytic infiltrate (yellow indication). (B) Pancreatic parenchyma with acinar atrophy and degeneration (black indication). Dense lymphoplasmacytic infiltrate is visible (yellow indication), (C) On the right side of the image obliteration of the vein with the presence of recanalization (black indication) is seen. (D) CD20: CD20+ lymphocytes form a secondary lymphoid follicle, (E) CD3: CD3+ lymphocytes are abundant, forming clusters and are mostly arranged around blood vessels. (F, G) KAPPA&LAMBDA: The increased number of polyclonal plasmacytes are highlighted by the Kappa and Lambda immunohistochemical stains. (F) KAPPA, (G) LAMBDA. (H) IgG: Clusters of IgG positive plasmacytes, seen in pancreatic parenchyma and surrounding pancreatic acini. (I) IgG4: The majority of IgG positive plasmacytes surrounding atrophic pancreatic acini are IgG4. Darkly stained cells are considered positive. Arrows and annotations in the images point to regions of fibrosis, lymphoplasmacytic infiltrate, acinar atrophy, vein obliteration, secondary lymphoid follicles, clusters of lymphocytes, and plasmacytes. H&E – hematoxylin and eosin staining. CD20 and CD3 – immunohistochemical markers for lymphocytes. Kappa and Lambda – immunohistochemical markers for polyclonal plasmacytes. IgG and IgG4 – immunohistochemical markers for IgG- and IgG4-positive plasmacytes; Staining method – hematoxylin and eosin; CD20, CD3, Kappa, Lambda, IgG, and IgG4 immunohistochemical stains.