The phenotype of IRTA1⁺ tonsil cells. (A) Double immunofluorescence staining of tonsil sections. IRTA1 is green. Negative control is red. No double-positive cells are identified (yellow-green). (B) IRTA1⁺ cells are CD20⁺ B cells; (inset) higher power of the same. (C) CD79a is weakly coexpressed on IRTA1⁺ B cells. (D) BCL2 is weak or negative on IRTA1⁺ extrafollicular B cells. The epithelium surface is at the top edge of the image. (E) CD3 and IRTA1 do not costain. (F) CD68 labels macrophages but not IRTA1⁺ B cells. (G) IRTA1⁺ cells and CD138 are mutually exclusive. (H) Rare interfollicular large cells (arrowheads) are IRTA1⁺ (green)/CD30⁺ (red) (green + red = yellow). All immunostaining for IRTA1 was performed with the specific polyclonal antibody. Original magnifications: × 400 (A-H); × 1000 (B inset).