Interfollicular large B cells stained with various markers. (A) Left panel: Nuclear expression (brown) of the mismatch repair enzyme MSH2 is seen in CD20⁺ (blue) interfollicular large B cells (seen at higher magnification in the inset). Right panel: Interfollicular large B cells express caspase-3 (brown); inset shows a caspase-3⁺ interfollicular large B cell at higher magnification. (B) The germinal center–associated markers CD10 (brown) and BCL-6 (brown) are absent from CD20⁺ (blue) interfollicular large B cells. Insets show the staining pattern of the interfollicular large B cells at higher magnification. Note expression of these markers in cells within lymphoid follicles (Foll). (C) Interfollicular large B cells do not express IgD or CD5 (double immunofluorescence labeling, with CD20 in red and the other markers in green, as also shown at higher magnification in the insets). Magnification is × 20 for all main images and × 40 for the insets.