Receptors and recognition mechanisms in intestinal infection

Commensal and pathogenic micro-organisms of the alimentary tract exhibit outstanding specificity with respect to host species, phenotype and age, and often to the type and location of epithelial cells within the gut. Specificity in attachment to the gut is achieved most commonly by ligand-receptor interactions at the pathogen-epithelial interface, commonly a bacterial lectin interacting with specific saccharides of the intestinal microvillus membrane. These bacterial lectins are usually associated with specialized attachment organelles known as pili or fimbriae. A variety of different bacterial pili have now been characterized with respect to their sugar specificities. Similar molecular events are important in the production of diarrhoea, notably the interaction of enterotoxins (cholera toxin, Escherichia coli toxins) with glycolipid receptors on the intestinal cell surface. In most instances, toxin-gut interactions exhibit less impressive specificity than is evident for attachment of micro-organisms to the intestinal epithelium. Identification and characterization of these processes has, and will continue to have, important implications for the biological control of enteric infection, particularly with respect to vaccine development.