A: Immunohistochemical stain for p21WAF1/Cip1 (brown nuclei) in a liver allograft biopsy with early CR. Note the BEC cytological alterations, including multinucleation (arrow), uneven nuclear spacing, and cellular enlargement, along with the increased p21WAF1/Cip1 nuclear labeling. B: Immunohistochemical stain for p21WAF1/Cip1 in primary cultures of mBEC (brown nuclei). Note the similarity between the damaged BEC in the bile duct with early CR (A and C) and the enlarged senescent mBECs in the primary cultures. Both cell populations show multinucleation and cytoplasmic enlargement and occasional cells show nuclear pyknosis. Note also that both the enlarged cells in the primary BEC cultures and the BECs in damaged bile duct express nuclear p21WAF1/Cip1, but smaller cells do not. C and D: Staining of serial sections from a biopsy with early CR for p21WAF1/Cip1 (C) and Ki-67(Mib-1) (D) shows that the BEC up-regulation of p21WAF1/Cip1 is not associated with mitotic activity.