home > Research > Host Bacteria Interaction
Host-Bacteria Interaction
Endogenous bacteria resident in our gut constantly interact with our immune system, starting from our birth, when our gastro-intestinal tract is rapidly colonised by bacteria coming from the maternal uro-genital tract and the enviroment. Intestinal microbes, infact, contribute to the maturation of the gut-associated lymphoid tissue (GALT) having a very important role in a precious event called "acquired immunity". Pioneer bacteria modulate gene expression in intestinal epithelial cells of the newborn, predisposing the environment to the subsequent bacterial colonisation.
Even if progress has recently been made in analyzing possible mechanisms involved in this exchange of information, a lot of work remains to be done.
Acquired or induced tolerance refers to the immune system's adaptation to external antigens. One of the most important natural kinds of acquired tolerance occurs during pregnancy, where the fetus and the placenta must be tolerated by the maternal immune system. Moreover, the establishment of a resident microbiota in our gastro-intestinal tract since birth contributes significantly to this mechanism, in order to create a balance between the ability of our immune system to recognise exogenous pathogens and, at the same time, to tolerate the presence and activity of endogenous beneficial and potentially harmful bacteria.
The interpretation of the constant dialogue between bacteria and our body, mediated by the immune system, requires deep investigations. A scheme of this complex dialogue is reported below.
(From: Blaise Corthesy, Rex Gaskins, Annick Mercenier (2007) Cross-Talk between Probiotic Bacteria and the Host Immune System. Journal of Nutrition 137, 781S-790S).
Ingested probiotics participate in this cascade of events by modulating mucosal receptors triggering signaling cascades that ultimately activate underlying immune cells in the lamina propria. Alternatively, probiotics may also release soluble factors that themselves stimulate signaling cascades
at the level of the epithelium or associated immune system.
Dialogue between probiotic bacteria and host involves diverse types of interaction, described below:
- adhesion to intestinal mucus and epithelium
- coaggregation with pathogens
- production of antimicrobials (organic acids, hydrogen peroxide, carbon dioxide, bacteriocins)
AAT can contribute to the elucidation of some of these mechanisms by studying, with in-vitro and ex-vivo assays, the behaviour of probiotics when a contact is established with host cells and/or pathogens. The evaluation of the ability of probiotics to trigger immunological responses in murine models and in humans represents one of the service that AAT can perform, together with its scientific partners.
The opportunity to pre-screen potential probiotic strains on the basis of the immunological profile they can induce in the host, is a very useful tool to orientate further applications of probiotics.
For more info please address to the following publications:
- Ignazio Castagliuolo, Francesca Galeazzi, Susanna Ferrari, Marina Elli, Deborah Tormen, Paola Brun, Giacomo C. Sturniolo, Andrea Cavaggioni, Lorenzo Morelli, Giorgio Palù (2005). Beneficial effect of Lactobacillus crispatus on experimentally induced colitis in mice: effect of different phenotypes. FEMS Immunol and Med Microbiol 43 (2): 197-204.
- Sandra Voltan, Ignazio Castagliuolo, Marina Elli, Stefano Longo, Paola Brun, Renata D'Incà, Andrea Porzionato, Veronica Macchi, Giorgio Palù, Giacomo C. Sturniolo, Lorenzo Morelli, Diego Martines (2007) Aggregating phenotype in Lactobacillus crispatus determines intestinal colonization and TLR2 and TLR4 modulation in murine colonic mucosa. Clin Vacc Immunol 14(9):1138-1148.
- Sandra Voltan, Diego Martines, Marina Elli, Paola Brun, Stefano Longo, Andrea Porzionato, Raffaele DeCaro, Giorgio Palù, Giacomo C. Sturniolo, Lorenzo Morelli, Ignazio Castagliuolo (2008) H2O2 as a signal transducing molecule in Lactobacillus crispatus M247 induced PPAR? activation in the intestinal mucosa. Gastroenterology 135(4):1216-27.
- Siciliano RA, Cacace G, Mazzeo MF, Morelli L, Elli M, Rossi M, Malorni A. Proteomic investigation of the aggregation phenomenon in Lactobacillus crispatus. Biochim Biophys Acta. 2008 Feb;1784(2):335-42. Epub 2007 Nov 22.