HEMATOPOIETIC STEM-CELL MARKERS ARE EXPRESSED BY DUCTAL PLATE AND BILE-DUCT CELLS IN DEVELOPING HUMAN LIVER

The identification of ductal plate cells as likely progenitors for bile duct epithelium and hepatocytes and their possible reappearance as oval cells in the regenerating liver have generated much interest in their pluripotential capacities, We have examined the distribution of three hematopoietic stem cell markers, c-kit, CD34, and CD33 in addition to laminin, the standard cytokeratin markers CAM 5.2, CK 18, and CK 7 and the oval cell marker OV-6 in fetal liver during various stages of development. Hematopoietic stem cell markers were expressed in ductal plate cells in a pattern similar to the early cytokeratin markers CAM 5.2 and CK 18, Cells stained strongly for these early cytokeratin markers until 22 weeks. Thereafter, the expression of these markers decreased while positivity for CK 7 increased. Bile duct cells showed a distribution of hematopoietic and cytokeratin markers resembling that of ductal plate cells. Both ductal plate cells and bile duct cells expressed OV-6 strongly throughout development. This study showed similarity between hepatic and bile duct precursors and bone marrow stem cells. The comparable distribution of markers in bile duct epithelium and ductal plate cells may imply fewer transitional stages between ductal plate cells and bile duct epithelium than between the putative stem cells and hepatocytes.