Abstract
Endogenous peroxidase is the cytochemical marker used to identify Kupffer cells in the adult liver. In this study, we show by ultrastructural cytochemistry that Kupffer cells of the fetal rat liver are endogenous peroxidase positive. The reaction product is localized in the endoplasmic reticulum including the perinuclear cisternae and in a few lysosome-like dense bodies. Serial sections of Golgi regions suggest that GERL and not the Golgi stacks, is peroxidase positive. As in the adult liver, peroxidase is not localized in endothelial cells. Kupffer cells do not appear to transform from endothelial or extravascular developing monocytic cells and are present prior to bone marrow formation. The relevance of these observations with respect to the possible origin of the Kupffer cell is discussed.