Figure 2. Immunohistochemical characteristics of the plasma cell infiltrate. (A) A CD138 marker highlights the prominent plasma cell component of the inflammatory infiltrate (original magnification 100×). (B) Most of the plasma cells show expression of immunoglobulin G (IgG) (original magnification 200×). (C) An IgG4 marker shows that more than 70% of the IgG-positive plasma cells express IgG4 (original magnification 200×). (D) In a high-power view, the number of plasma cells expressing IgG4 is in excess of 50 cells per high-power field (original magnification 400×). The findings in C and D reflect an increased number of IgG4-positive plasma cells beyond the cut-off value for the diagnosis of IgG4-related disease.