Overview of Gut Immunology -- The Commensal Microbiology of the Gastrointestinal Tract -- Overview of the Gastrointestinal Microbiota -- Effects of Microbiota on GI Health: Gnotobiotic Research -- Positive Interactions with the Microbiota: Probiotics -- Negative Interactions with the Microbiota: IBD -- Diet, Immunity and Functional Foods -- Host-Microbe Communication within the GI Tract -- Host-Microbe Symbiosis: The Squid-Vibrio Association-A Naturally Occurring, Experimental Model of Animal/Bacterial Partnerships -- The "Microflora Hypothesis" of Allergic Disease -- The Damage-Response Framework of Microbial Pathogenesis and Infectious Diseases. The idea that the microbial communities within the GI tract have a profound influence on general human health actually originated with Russian scientist Elie Metchnikov at the turn ofthe last century. Also known as the "fatherofimmunology", Metchnikovbelievedthat putrefactivebacteriain the gut were responsible for enhancing the aging process. He theorized that ingestion ofhealthy bacteria found in fermented foods could counteract toxic bacteria and was the key to good health. His theories concerning good bacteria and health can be found in his treatise "The ProlongationofLife: Optimistic Studies".Thesewritings promptedJapanesescientist Minoru Shirotatobegin investigationofhow fermentative bacteriaimprove health. He succeededin isolating astrainofLactobacillusthat could survive passage through the intestine, while promoting a healthy balance ofmicrobes. The "Shirota strain" is still used today in the fermented beverage Yakult.It is clear from a commercial standpoint that these ideas have inspired the development of a probiotic industry, which has expanded greatly in the U.S. over the past 5-10 years.