Different immune responses of dendritic cells induced by Lactobacillus paracasei strains.

Many studies provided evidence that intestinal microbiota, including probiotic bacteria, can modulate the gut immune system(1). It is also recognized that different strains of the same bacterial species may differentially polarize the immune response. Considering the importance of the species Lactobacillus paracasei, also frequently isolated from different foods, we evaluated the ability of five genetically characterized L. paracasei strains to modulate the activity of mouse dendritic cells (DCs), which are potent antigen-presenting cells and can effectively induce primary immune responses. The results indicated that all the strains stimulated the phenotypic maturation of DCs, but cytokine profiles revealed a different secretion of interleukin IL-2, IL-12 and IL-10 by DCs. Specifically two strains, IMPC 4.1 and ATCC 334, stimulated the highest levels of IL-2 and IL-10. In this regard, IMPC 4.1 can be considered particularly efficient as an anti-inflammatory/regulatory strain. Other two strains, IMPC 2.1 and LMG P-17806, previously identified as probiotic strains, were characterized by an intermediate ability to induce cytokine secretion. While strain LMG 23554, characterized by a potential pathogenic behavior, was differentiated from the others by a very low ability to induce IL-10 and IL-12 secretions. In conclusions, our results indicate that the evaluation of types and/or levels of secreted cytokines by DCs could be relevant to define pro- or anti-inflammatory properties of a bacterial strain and its more appropriate clinical use. Moreover, a very low ability of a strain to induce cytokines secretion could suggest that further investigations are required to evaluate its possible use as a probiotic.