An electron microscopy study of Kupffer cells in livers of mice having Friend erythroleukemia hepatic metastases.

Kupffer cells, which are part of the reticuloendothelial system, play an important role in clearing pathogenic substances, including tumor cells, from the liver. The role of Kupffer cells in tumor development is very important as Kupffer cells can be manipulated to a tumoricidal state with biological response modifiers to kill tumor cells and thus to decrease tumor burden and extend survival time. To gain additional information on the role of Kupffer cells and their interaction with tumor cells in hepatic metastases, we studied an established experimental hematogenous metastatic model (Friend erythroleukemia) in mouse livers by light and electron microscopy. Highly activated Kupffer cells were observed in close contact with tumor cells in sinusoids and also in tumor forming foci within the hepatic parenchyma. The Kupffer cells were activated by the presence of the hematogenous tumor cells and were able to lyse and phagocytose them. However, some tumor cells evaded the Kupffer cells as metastases still occurred. Kupffer cells and other macrophages were found to leave the sinusoids and migrate to sites of potential tumor development where they interacted with tumor cells and intimately wrapped their processes around fat storing cells. It is possible that these macrophages which cross biological barriers could be used to deliver drug-loaded microparticles (liposomes and microcapsules) to tumors.