Figure 1. Immunohistochemical staining of p16^INK4a, p21^WAF1/CIP1, p27^KIP1, and p53. Representative fresh-frozen sections of human corneas from donors at various ages (A: p16, 18 years; B: p21, 33 years; C: p27, 54 years; D: p53, 18 years; E: control, 68 years) are shown. Positive staining for all four senescence-related genes are clearly visible in the endothelial nuclei. Magnification; 400×.