Probiotic microorganisms, especially lactic acid bacteria, are effective in the treatment of infectious diarrhoeal diseases and experimental colitis. Although the mechanisms by which these organisms exert their anti-inflammatory effects are largely unknown, immunomodulating effects are suggested. The objective of this study was to examine the effect of a 5-week oral administration of Lactobacillus rhamnosus subspecies GG (Lb. GG) on the cellular immune response to intestinal microorganisms in ten healthy volunteers. Peripheral blood cells (PB) were stimulated with either ‘self’ or ‘non-self’ preparations of faecal samples and isolated Bacteroides fragilis group-organisms (Bfg) or Escherichia coli (Esch. coli), and pro- and anti-inflammatory cytokines (IL-10, IL-4, IL-6, IFN-γ, TNF-α) were measured in the culture supernatant. CD4+ T-lymphocyte activation was determined by measurement of intracellular ATP following lysis of the cells. The activational response of CD4+ T-lymphocytes towards isolated and heat-inactivated intestinal organisms was increased after the probiotic treatment. Additionally, TNF-α, IL-6 and in part IFN-γ cytokine secretion by PB cells following stimulation with whole stool preparations and single members of the flora was significantly decreased, whereas the IL-10 and in part IL-4 cytokine secretion was increased at the end of the study. In contrast, the activational response of CD4+ T-lymphocytes following stimulation with whole ‘non-self’ intestinal flora was higher than by ‘self’ intestinal flora, but both responses showed a trend towards a reduction at the end of the study. This study documents a direct effect by Lb. GG on the cellular immune system of healthy volunteers and offers a promising tool to investigate systemic immunomodulation due to oral administration of probiotic microorganisms.

This paper reviews the evidence for the claims of health benefits derived from the use of probiotics. A brief history of probiotics and the types of probiotics currently used and the criteria for the selection of probiotics is discussed. The ability of probiotics to enhance the nutritional content and bioavailability of nutrients and the scientific evidence for the usefulness of probiotics in alleviating the symptoms of lactose intolerance and in enhancing growth development is examined. The remainder of the review focuses on studies of a specific probiotic, Lactobacillus GG which has been extensively investigated for its health benefits in humans and animals. These studies serve as a model for the potential benefits of probiotics. The ability of Lactobacillus GG to treat or prevent diarrhoeal disease, to serve as an adjuvant for vaccines, to prevent rotavirus-induced diarrhoea, to prevent milk-based allergic reactions, alcohol-induced liver disease and colon cancer are presented. The review concludes with a discussion of the data supporting the safety of probiotics.