Tumors, cell contact

The body s cells are normally subject to strict social control. They only divide until they come into contact with neighboring cells cell division then ceases due to contact inhibition. Exceptions to this rule include embryonic cells, cells of the intestinal epithelium (where the cells are constantly being replaced), cells in the bone marrow (where formation of blood cells takes place), and tumor cells. Uncontrolled cell proliferation is an important indicator of the presence of a tumor. While normal cells in cell culture only divide 20-60 times, tumor cells are potentially immortal and are not subject to contact inhibition. 

Once in contact with the tumor cells, LCM are internalized bringing their content into the cell cytoplasm. Most 9L and C6 tumor cells examined appear to have LCM in their cytoplasm 2 min after LCM i.v. injection. This uptake was observed by confocal... 

Even though sometimes malignant cells arrested in the microcirculation do not migrate further into the organ parenchyma, and grow locally in an expansive fashion until they rupture the vessel wall (Kawaguchi et al., 1983 Crissman et al., 1985 Lapis et al., 1988), in most eases the contact between tumor cells and the endothelium results in EC retraction, with exposure of the underlying BM, followed by invasion of tumor cells in the tissue. Electron microscopy observation on the formation of pulmonary metastasis has shown in-... 

During intravasation and extravasation, tumor cells must traverse not only the BM barrier but also the continuous layer of endothelial cells which lie on the BM. Adhesion to, separation of and intrusion into endothelial (or epithelial) cells are as crucial to tumor spread as degradation of the extracellular matrix. Crissman et al. (1985) estimate that the endothelial cell layer may delay tumor cells from contacting the BM in vivo for up to 2 days. 

Alternatively, co-culture of tumor and host cells can be made so that the two cell types are either in the same, or in separate compartments, with or without direct cell contact. Effects on tumor cell growth in the absence of direct cellular contact suggests the presence of soluble, secreted factor(s), whereas when the growth effects require direct cell contact it is a hint that the responsible growth factor(s) are insolubilized either on the cell surface, or in the BM. 

Co-culture without direct cell-to-cell contact. This type of coculture can be achieved in two different ways. In the first way, host cells are plated onto the bottom well of a transwell plate system, while tumor cells are plated in the transwell, on a tissue culture-treated membrane, with pores smaller than 3 /zm, so to prevent migration of the cells across the membrane. The two cell types can... 

During the metastatic process malignant tumor cells come in contact with many components of the immune system, and only if able... 

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