Distribution of Notch-1, Stro-1, VCAM-1, and Sox9 in normal human adult articular cartilage. (a) Percentage positive signal for the superficial zone (SZ), middle zone (MZ), and deep zone (DZ). *P < 0.05. (b) Representative images (10×) for Notch-1, Stro-1, VCAM-1, and Sox9 showing greater staining frequency in the SZ and upper MZ. (c) Images depicting SZ and upper MZ (40×). Solid inset (bottom right) indicates negative controls. Dotted line box outlines SZ images presented in (d) showing a mix of cells that are positive (black arrow) or negative (white arrow) for each immunostain. (e) Stro-1 (brown) and Sox9 (red) double staining with some cells single Stro-1 positive (white arrow) or Stro-1/Sox9 double positive (black arrow) (40×).