Shigella: rupture, invasion and destruction of the colonic epithelium

Crossing the epithelial barrier: Shigella acts on the immune system in orde r to cross the intestinal epithelial barrier which is normally impermeable to intestinal flora. Among the effectors of the immune system of the coloni c mucosa are translocation sites corresponding to lymphatic follicles carry ing a follicular epithelium in the presence of M cells. These cells capture molecules, particles and microorganisms from the intestinal barrier that t hey translocate to immune competent cells present in the follicles (antigen presenting cells including resident macrophages and then B and T lymphocyt es). Macrophage aptotosis and its consequences: The first cell infected by Shige lla appears to be the macrophage once the translocation has been made via t he M cells. This infection rapidly leads to apoptotic death of the macropha ge allowing the Shigella to infect the laterobasal epithelial cells and the development of an inflammatory/response. This response in rum facilitates the invasion, rupture and permeability of the intestinal epithelium and the initiation, by Shigella, of a cell-to-cell invasion pathway. (C) 2000, Mas son, Paris.