Beneficial effect of probiotics in IBD

Abstract

Although the beneficial capacities of probiotics are more and more sub- stantiated, their effects clearly depend on the strains used and their mechanisms of action remain poorly understood. Recent evidences have highlighted the poten- tial role of cell-wall components in the anti-inflammatory capacity of selected lactobacilli. In this addendum, we sum- marize our recent results concerning the role of peptidoglycan (PGN) and NOD2 signaling in the regulation of intestinal inflammation. We showed that the pro- tective effect of Lactobacillus PGN is strain-specific and linked to the induc- tion of diverse immune regulatory path- ways. Moreover the beneficial effect of Lactobacillus PGN correlated with the release of a specific muropeptide sensed by NOD2. These findings allow for a better understanding of how probiotic lactobacilli exert their beneficial effect and will help guide for more successful strain selection. Introduction The interaction between the host and its gut microbiota is now well recognized to play a crucial role in the establishment of mucosal immunity and the maintenance of intestinal homeostasis. To maintain a symbiotic crosstalk, our immune system has to discriminate between commensal/ beneficial bacteria and pathogenic micro- organisms. Breakdown of this equilib- rium, leading to microbial dysbioses and deregulated mucosal immune responses, has been associated with chronic dis- ease such as inflammatory bowel disease (IBD).1 Probiotics, live microorganisms which exert beneficial health effects, have been used more or less successfully in IBD patients and their protective effects clearly depend on the strains used. Even if the understanding of their mechanisms of action recently improved consider- ably, many questions remain unanswered and useful biomarkers allowing to select potent strains are still lacking.2 How can probiotics impact on mucosal immunity? How can they modulate host signaling pathways? What are the bioactive com- ponents involved? What can explain their strain-specific capacities? Here we aim to present some of our recent advances try- ing to answer these types of questions. We thereby focus on the mechanisms by which lactobacilli can induce regulatory responses to dampen inflammation and highlight the crucial role of cell wall com- ponents in this process.