In vitro effect of levan-activated macrophages on Lewis lung carcinoma cells

The polysaccharide levan (polyfructose) has previously been shown to exert an inhibitory effect on the growth of several murine tumors. This activity is mediated by a host reaction, involving mainly macrophages but also other elements of the immune system. It was not clear, however, whether levan-activated macrophages act by a direct cytocydal effect on the tumor cells or via the activation of a specific immune response to the tumor. In the present study, the possibility of a direct cytotoxicity of levan-activated macrophages against Lewis lung carcinoma cells was tested by coculture in vitro. It was found that levan-induced (as well as paraffin oil induced) macrophages actually exert a direct cytotoxic effect on Lewis lung carcinoma cells. The tumor cell killing is mediated by cell to cell contact. A cytoplasmic bridge was often seen between the macrophage and the tumor cell. The remaining tumor cells in the lysed area appear slender, shrunken and non-dividing.