Intestinal bacteria play a pivotal role in shaping gut immunity. Epidemiologic evidence also suggests that Lactobacilli and Bifidobacteria are key players inthis context. Furthermore, literature data reported that the immune modulatory activity of generally recognized as safe (GRAS) bacteria could be associated with the secretion of specific molecules, like enzymes or other unidentified substances. Based on these findings, the general objective of this Doctoral Thesis was to evaluate the modulation of the immune response by using different bacterial populations, isolated from the human intestine, or already availableas GRAS stains, according with the American FDA designation. Both in vitro(Caco-2cell line and mouse dendritic cells) and in vivo (HLA-DQ8 transgenic mice) models were adopted to address this issue. In the first study, the immunomodulatory effects of various probiotic strains of L. paracaseion dendritic cells were determined. We found that bacterial metabolites from only some of tested strains showed an anti-inflammatory activity.
In a second study,another GRAS bacterial strain, Streptomyces mobaraensis, was assessed. In particular, newculture conditions were developed to optimize the secretion of microbial transglutaminase (mTG), previously found to be able to block the inflammatory response induced by gluten in Coeliac disease (CD) patients. Importantly, we found that wheat flour treated with sterile-filtered supernatant of S.mobaraensis culture, resulted also effective in modulatingthe immune response to gluten. Furthermore, bread manufactured with treated flour had only minor changes in the baking parameters.
In other two studies, we specifically focused on the relationship between the dietary habit and immunomodulatory abilities exerted in vitro by intestinal Bifidobacteria and Lactobacilli, isolated from individuals following omnivorous, vegetarian and vegan diets. Interestingly, both lactobacilli and Bifidobacteria showed a genus-specific ability of modulating in vitro innate immunity associated with a specific dietary habit.
In conclusion, these data highlighted different applications of GRAS bacteria and their metabolites with possible implications for the management of inflammatory diseases like CD
