Proliferation and growth arrest in AID⁺ DZ and OZ GC cells. (A) A single GC was imaged with 4 sets of triple staining for AID, CDKN1B (p27), Ki-67, BCL6, TP53, and CCNB1. Each stain is shown as single color at low power. Original magnification ×10. Note at the right, TP53⁺ basal epithelial layer (arrow). The DZ and OZ areas enlarged below (original magnification ×40) are shown as white rectangles. (B) The DZ is homogeneously CDKN1B^–; circled in the OZ is a cytAID⁺, BCL6⁺dim, CDKN1B⁺dim cell. A diamond highlights a nAID⁺, BCL6⁺dim, CDKN1B^– cell. (C) DZ AID⁺ cells are Ki-67⁺ and CDKN1B^–. In the OZ, a cytAID⁺, Ki-67⁺, CDKN1B⁺dim cell is circled. A diamond shows a nAID⁺, Ki67⁺, CDKN1B^– cell. (D) At the outer border of the DZ and OZ, cytAID⁺ BCL6^– cells (circles) shows TP53. A nAID⁺, BCL6⁺, TP53^– cell is indicated by a diamond. (E) A portion of the DZ shows a CCNB1^–nAID⁺ small centroblast (diamond), a rare CCNB1⁺ nAID⁺ centroblast (square), and a mitotic cell (circle) in which AID and CCNB1 are cytoplasmic. Scale bar: 1 μm at ×40 and 4 μmat ×10.