IgG4-related lymphadenopathy (type IV). (a) The lymph node shows marked follicular hyperplasia with PTGC. (b) The PTGCs appear as round to oval structures 2-3 times the diameter of the other reactive follicles. (c) Numerous eosinophils infiltrate the interfollicular zone. (d) The majority of IgG4+ plasma cells reside in the germinal centers, with a small number present in the interfollicular zone. (e), (f): The IgG4+/IgG+ plasma cell ratio is >40% (e: IgG4-immunostain, f: IgG-immunostain).
