Microbes in Gastrointestinal Health and Disease Andrew S. Neish  Gastroenterology  Volume 136, Issue 1, Pages 65-80 (January 2009) DOI: 10.1053/j.gastro.2008.10.080 Copyright © 2009 AGA Institute Terms and Conditions

Figure 1 Mechanisms of microbiota and gut crosstalk. Both parties in the symbiotic dyad possess means to alter and shape each other, resulting in a “negotiated settlement” at equilibrium. A breakdown on this crosstalk may result in a “dysbiotic” microbiota and clinical consequences. Gastroenterology 2009 136, 65-80DOI: (10.1053/j.gastro.2008.10.080) Copyright © 2009 AGA Institute Terms and Conditions

Figure 2 Cellular consequences to bacterial stimuli. Bacterial MAMPs may stimulate pattern recognition receptors (including extracellular TLRs and formylated peptide receptors, or intracellular Nods). Intensity, duration, and spatial origin of the subsequent signaling responses are integrated by an intricate and interrelated network of transduction pathways that determine if MAMP perception warrants a “low gain” cytoprotective response, a “medium gain” inflammatory reaction, or “high gain” programmed cell death result. Gastroenterology 2009 136, 65-80DOI: (10.1053/j.gastro.2008.10.080) Copyright © 2009 AGA Institute Terms and Conditions

Figure 3 Preferred sites of commensal/probiotic interaction with the gut. Cecum/ascending colon is a “bioreactor” with the greatest amounts of bacteria, metabolic activity, and SCFA fermentation. Concentration of SCFA diminishes along the colon. The distal ileum is enriched in GALT (Peyer's patches) and is the dominant site of luminal sampling and mucosal adaptive immune activity. Gastroenterology 2009 136, 65-80DOI: (10.1053/j.gastro.2008.10.080) Copyright © 2009 AGA Institute Terms and Conditions