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 bil e duct epithelium and hepatocytes and their possible reappearance as o val cells in the regenerating liver have generated much interest in th eir pluripotential capacities, We have examined the distribution of th ree 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 mar kers until 22 weeks. Thereafter, the expression of these markers decre ased while positivity for CK 7 increased. Bile duct cells showed a dis tribution of hematopoietic and cytokeratin markers resembling that of ductal plate cells. Both ductal plate cells and bile duct cells expres sed 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 duc tal plate cells may imply fewer transitional stages between ductal pla te cells and bile duct epithelium than between the putative stem cells and hepatocytes.