Plasticity of the gastrointestinal epithelium: The M cell paradigm and opportunism of pathogenic microorganisms

The maintenance during adult life of a large spectrum of pluripotency by stem cells originating from the endoderm seems to be the grounds for the striking plasticity of the digestive epithelium, which is able to drastically modify its differentiation pattern depending on the microenvironment. As a paradigm, Peyer's patch M cell development appears to be induced by crosstalk between lymphoid cells and/or microorganisms. Examples of pathological transdifferentia- tion of epithelia, also described as `metaplasia' and affect- ing various organs, support the concept of intestinal plastic- ity. Though, the molecular processes involved in epithelial transdifferentiation have not been identified, histological analyses of these metaplastic tissues and experimental induc- tion of transdifferentiation of normal epithelia provide lines of evidence suggesting that a modification of the local environment, such as occurs during contact of the epithe- lium with lymphoid cells or microorganisms, plays a key role in this process.