DUCTULAR REACTION AFTER SUBMASSIVE NECROSIS IN HUMANS - SPECIAL EMPHASIS ON ANALYSIS OF DUCTULAR HEPATOCYTES

The ductular reaction to acute submassive necrosis was studied in huma n livers removed at the time of orthotopic liver transplantation Singl e, double, and triple immunohistochemical labeling itt combination wit h morphometry was used to analyze the phenotype and proliferative and apoptotic rates of various epithelial cell compartments. These were di vided on the basis of immunohistochemistry and morphology into three s ubtypes: 1) CK19(+)/AE1(+) mature bile duct epithelium, 2) HEP-PAR(+) mature hepatocytes (HEPs), and 3) CR19(+)/AE1(+) ductular hepatocyte C DH) cells lying at the interface between the portal tract connective t issue and the hepatic lobules. Cycling cells were defined as those sho wing Ki-67(+) (MIB-1) nuclear labeling Apoptotic cells were identified with in situ labeling using the terminal deoxynucleotidyl transferase -mediated dUTP-digoxigenin nick, end labeling assay. Special emphasis was placed on DHs that appeared at the interface between the portal tr acts and hepatic lobules. During the recovery phase from submassive he patic necrosis, subtraction of the rate of cell death from the prolife rative index shows that all of the epithelial compartments experience a net increase in the number of cells. The highest proliferation rate occurs in the DHs, which is significantly (P < 0.0001) higher than the proliferation race seen in either the HEP or bile duct epithelium com partments. Immunohistochemical analysis of the highly proliferative DH compartment shows it to be a heterogeneous population with unique phe notypic features. Like epithelial cells in the ductal plate of fetal l iver and cholangiocarcinomas, DHs are positioned on a laminin-rich mat rix and focally express vimentin and Lewis(X) and show up-regulation o f bcl-2 and type IV collagenase However, unlike ductal plate cells, DH s are CD34 and alpha-fetoprotein negative Although a subpopulation of DHs share phenotypic features with mature bile duct epithelium (AE1/cy tokeratin 19 and type IV collagenase positive) or HEP (HEP-PAR, albumi n, and alpha-1-antitrypsin positive), they are also clearly separate f rom both populations; DHs are negative or only weakly stain for glutat hione-S-transferase-pi and are type IV collagenase positive. Moreover, occasional DHs also co-expressed HEP-PAR or alpha-1-antitrypsin and A E1, indicative of both hepatocyte and ductular differentiation. These findings suggest that DHs seen in human livers after submassive necros is may represent a transient amplifying population arising from a prog enitor population located in or near the canals of Herring. In additio n, injured hepatocytes cart express cytokeratin 19 and AE1, which norm ally are biliary intermediate filaments.