Enhancement of lipid phagocytosis by cloned cells derived from rat malignant fibrous histiocytoma under hyperlipemic conditions.

The histogenesis of malignant fibrous histiocytoma (MFH) was studied by observing the influence of hyperlipemic (HL) conditions on the behavior of cloned MT-8 cells with an undifferentiated mesenchymal character and MT-9 cells with histiocytic and fibroblastic features, both derived from a spontaneous rat MFH. The cells were grown in medium containing 10% normal rat serum (CSM) or 10% HL rat serum (HSM) for 1, 3, 8 and 24 h. The cells grown in HSM showed a time-dependent, significant increase in numbers of cytoplasmic lipid droplets per cell and cells positive for acid phosphatase (ACP) and non-specific esterase (NSE) compared with cells grown in CSM. The number of cells positive for two different anti-rat monocyte/macrophage monoclonal antibodies (ED-1 and ED-2) also increased significantly in HSM. This histiocytic nature was confirmed by electron microscopy. Tumors were induced by inoculating MT-8 and MT-9 cells into rats on a standard diet and rats on a HL diet. MT-8 and MT-9 tumor cells in HL rats phagocytized lipid droplets and showed stronger positive reactions for ACP and NSE compared with tumors in control rats. These results imply that xanthomatous cells in MFH may be a phenotype of MFH cells expressing an enhanced histiocytic nature. MFH cells seem to alter their behavior depending on cultural or microenvironmental conditions.