Intestinal non pathogen-bacteria. Influence on mucosal immune system

A. DE MORENO DE LEBLANC

Mar del Plata, Buenos Aires, Argentina

Congreso; LIV Reunión Cientifica de la Sociedad Argentina de Investigacion Clinica. LVII Reunion Cientifica de la Sociedad Argentina de Inmunologia; 2009

Sociedad Argentina de Investigacion Clinica y Sociedad Argentina de Inmunologia

The gastrointestinal tract is a complex ecosystem where the host cells, intestinal microbiota and nutrients are in permanent contact with each other. The intestinal microbiota have many functions such as the participation in digestion and absorption of nutrients, the transformation of biliary salts, the production of different metabolites, the synthesis of vitamins and the production of enzymes. They play an important role on modulation of the immune system. The intestinal microbiota is involved in the development and maturation of the immune system maintaining the associated immune cells and oral tolerance. Probiotic microorganisms can exert an influence on the intestinal microbiota and through this effect can indirectly affect the mucosal immune system. In this sense, the down regulation induced by a probiotic fermented milk, administrated in early periods of the life, was demonstrated. Lactic acid bacteria (LAB) are the microorganisms most commonly used as probiotics. Immune system stimulation is one of the many beneficial effects reported for these bacteria when are administered orally. The viability of LAB is important factor to consider when evaluating their immune modulation properties; furthermore, this characteristic is dependent of the bacterial strain. The study of cytokines and cell receptors in lamina propria of the intestine and epithelial cells allows us to suggest the possible mechanisms involved in the modulation of intestinal immunity: LAB or bacterial particles come into contact with epithelial and immune cells thought receptors such as TLR and mannose receptor (CD206). This stimulus activates different immune cells (principally cells from the innate response) that produce an important cytokine profile. This effect was different for each bacterial strain and when the probiotic bacteria where administered into a fermented product suggesting that in the latter case, other non-microbial components can also exert a beneficial effect. However, all the assayed probiotic microorganisms and fermented products maintained the balance between pro-inflammatory and regulatory cytokines. Considering that inflammatory bowel diseases may result from exaggerated stimulation of the mucosal immune system by luminal bacterial biota and that probiotic bacteria can exert a beneficial influence on this microbiota, probiotic bacteria and fermented products could be useful to regulate this immune response. In this sense, yoghurt feeding was able to reduce the acute intestinal inflammation and also attenuated the symptoms of recurrent intestinal inflammation in mice models. This effect could be mediated by desirable changes observed in the intestinal microbiota with increases of bifidoabacteria population which was related with a regulatory intestinal immune response (high production of IL-10 and decrease of IL-17). We demonstrated using mouse models that the prolonged consumption of fermented milks can modulate the mucosal immune system and maintain it in a state of surveillance to confront different pathologies such as cancer, inflammation or infections. We can also conclude that the innate immune response would be the principal response induced by non pathogenic probiotic microorganisms at the mucosal level.