Expression of SDF-1α in the human thymus.

Frozen sections of human thymus were double stained with anti–SDF-1α alone (red fluorescence; A) or in combination with anti–TE-4 (green fluorescence; B,C), anti–TE-3 (green fluorescence; D,E), or anti–type I collagen (green fluorescence; F,G). SDF-1α expression is detected in TE-4⁺ epithelial cells (yellow cells, arrows) appearing in the thymic subcapsular (C) and medullary areas (B). Note the absence of SDF-1α expression in TE-3⁺ cortical epithelial cells (D,E), and type I collagen-positive fibroblasts (F,G). SC indicates subcapsullary area; C, cortex; M, medulla; HC, Hassal corpuscle; V, blood vessel. Original magnifications: panel A, × 50; panels B, E, and G, × 250; panel C, × 150; and panels D and F, × 75.