Barbara J. Clement

　　Department of Food Science and Technology, University of Nebraska-Lincoln, A

　　The Food and Agricultural Organization of the United Nations and the World Health Organization defines probiotics as living microorganisms, which, when consumed in adequate amounts, confer a health benefit on the host. Since the early 1900s, when Ilya MetcUShnikoff was attempting to extend human longevity by introducing fermentative bacteria involved in yogurt product, the idea of being able to modify the gut microflora for health improvement has taken hold in both scientific and not-so-scientific groups. Despite contradictory findings, the overall impression of the efficacy of probiotics seems to lean toward a benefit, or at least no harm. It was accepted at one time that the introduced organisms would most likely have to maintain a presence in the gut microflora, where it was assumed that they would presumably apply their effect through interaction with, or replacement of, some of the normal microflora. The actual mechanism for any beneficial effect has been difficult to discern in practice. However, it seems that probiotic organisms may effect a positive response through the modulation of signaling within the gut flora and/or the mucosa and related structures. Signaling may take the form of cell-to-cell communication or modulation of the immune response through interference with pathogen receptors, cytokine production, or allergen response. It has been demonstrated in cell culture that immunomodulation, such as inhibition of cytokine signaling and interference with receptor-mediated signal transduction, accounts for at least part of the positive effect of these organisms on the gut mucosa. Demonstrated signaling mechanisms will be reviewed with an eye to gaps in knowledge and future applications.