Case of 54-year-old woman with prominent reactive follicular hyperplasia. On closer inspection, numerous intrafollicular plasma cells are present all of which express IgG4 subtype on IHC for IgG4.

Normal lymphoid follicles do not contain any plasma cells and most plasma cells should be restricted to the medullary cords. In autoimmune condition, intrafollicular plasma cells frequently accumulate and in IgG4-related systemic processes, numerous intrafollicular plasma cells expressing IgG4 subclass are characteristically noted. They may occasionally be associated with perifollicular granulomas.