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In vitro effect of levan-activated macrophages on Lewis lung carcinoma cells
Abstract:
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 cytocidal 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.
Insights
The polysaccharide levan directly kills Lewis lung carcinoma cells. Levan-activated macrophages mediate this tumor cell killing through direct cell-to-cell contact in vitro.
Area of Science:
- Immunology
- Oncology
- Biochemistry
Background:
- The polysaccharide levan (polyfructose) inhibits murine tumor growth.
- Levan's anti-tumor activity involves host immune responses, particularly macrophages.
- The mechanism of levan-induced macrophage anti-tumor activity (direct cytotoxicity vs. immune activation) was unclear.
Purpose of the Study:
- To investigate the direct cytotoxic effect of levan-activated macrophages on Lewis lung carcinoma cells in vitro.
- To determine if macrophages activated by levan can directly kill tumor cells.
Main Methods:
- Coculture of levan-induced macrophages with Lewis lung carcinoma cells in vitro.
- Microscopic observation of macrophage-tumor cell interactions.
Main Results:
- Levan-induced macrophages exhibit direct cytotoxicity against Lewis lung carcinoma cells.
- Tumor cell killing is mediated by cell-to-cell contact, with observed cytoplasmic bridges.
- Remaining tumor cells showed signs of lysis, appearing slender, shrunken, and non-dividing.
Conclusions:
- Levan-activated macrophages possess direct cytotoxic capabilities against Lewis lung carcinoma.
- Direct cell-to-cell contact is the mechanism by which these macrophages kill tumor cells.
- This study clarifies a key aspect of levan's anti-tumor immune response.