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Micrometastasis are defined by the existence of cells or groups of cells in target organs. In the particular cas of colon cancers, although lymph node involvement is frequent, metastatic medullary involvement (while rarely at the origin of identified metastasis) can also be observed. Furthermore, micrometastatics cells can be identified in the circulating blood. This research relies on recent technics of immunocytochemistry with image analysis or molecular biology technics (generally PCR or RT-PCR). It is essential to have a specific reliable marker of metastatic cells. The prognostic value of identifying micrometastasis in organs also remains to be defined.

Bacterial enterotoxin receptors. Enteric bacterial toxins display a great diversity in their structure, molecular weight and mechanism of action. The interaction of enterotoxins with the intestinal mucosa either leads to a direct effect on the cell membrane or an effect on signal transduction within eukaryotic cells. However, before a toxin can affect a cell, it must after its secretion by a microorganism, recognise and bind to a specific surface molecule, its receptor. Membrane receptors of bacterial enterotoxins have been identified as protein, glycoprotein or glycolipid in nature. The chemical nature of the molecules acting as receptors is crucial and during evolution they have been carefully selected. Some toxins, after their interaction with a receptor molecule, will transduce a signal across the cell membrane while remaining at the cell surface. Other toxins, after this initial binding step with a receptor, will be internalised. Others can form pores leading to leakage of cellular components and cell lysis. Receptors that have been identified often comprise a saccharidic chain that is directly involved in the recognition and binding of the toxin. Today, models explaining toxin-receptor interactions are more complex, including multistep events. This review summarises the knowledge of the interactions between bacterial toxins and membrane receptors present on intestinal mucosa.

Bacterial enterotoxins, produced by some pathogenic bacteria, induce diarrhoea during human or animal digestive infections; most of them act via membrane receptors and are specifically recognized on the enterocyte brush border. These receptors differ in number (which probably determines the degree of enterotoxin toxicity, nature, structure, and specificity. The receptors, ie glycolipids (GM1) or glycoproteins, are well represented on the surface of the enterocyte, and/or in various vertebrate cell types. The enterotoxins bind to the receptor glucoside chains, in which sequences have sometimes been determined. In most cases irreversible binding occurs due to enterotoxin internalization.