Probiotics--industry myth or a practical reality?

Probiotics are "bacteria that are good for you' evolving out of the food industry, without quality data or a framework in which to function. This review asks three questions, the answers to which dictate the level of success that probiotics have had in moving into the medical model. How do they work? Evidence is summarised to show that (at least) certain bacteria activate Peyer's patch T cells to drive the common mucosal system via toll-like receptors on antigen presenting cells. They influence distant mucosal sites, promoting Th1 cytokine responses while downregulating Th2 responses. New data is included. Are all probiotics the same? They clearly are not - variation occurs between different isolates and importantly within isolates due to variable production/storage and poor quality control. These latter issues, together with poor clinical trials lacking surrogate markers of activation, have made clinical assessment very difficult. Do they have a role in man? Yes they do, but whether that is now or in the future largely depends on the quality of studies done. There is clear evidence in man that mucosal INF-gamma secretion is stimulated, indicating promotion of immune protection, downregulation of hypersensitivity disease and (yet to be demonstrated) enhanced apoptosis to reduce cancer risk. Preliminary evidence suggests that certain probiotics may regulate cytokine secretion around a mean, ensuring optimal protection without non-specific damage. Thus probiotics appear to restore defective immunity rather than stimulate, an observation relevant to restoration of Th1 immunity in infants.