Identification, localization, and purification of CD8⁺CD25⁺ human thymocytes. (A) Freshly isolated human thymocytes were assessed for expression of CD3, CD4, CD8, and CD25 by flow cytometry. Gated CD4⁺ (R1) or CD8⁺ (R2) SP thymocytes were assessed for CD3 and CD25. (B) Staining of a thymic section with anti-CD8 (bluish gray) plus anti-CD25 (red) mAbs. Arrows indicate cells showing double staining in the fibrous septa. (C) A consecutive section stained with anti-CD8 (bluish gray) plus isotype control (red) mAbs. (D) Staining of a thymic section with anti-CD8 (bluish gray) plus anti-CD25 (red) mAbs. Arrows indicate cells showing double staining in the medulla. (E) A consecutive section stained with anti-CD8 (bluish gray) plus isotype control (red) mAbs. Original magnification, ×400 for panels B-E.