Modulation of mouse dendritic cells in vitro by Lactobacillus gasseri postbiotic proteins

Different lactobacilli are probiotics for their beneficial effects that confer to the host. Recently, some of these effects were associated to released metabolic products/constituents (postbiotics). In the present study, the potential immunomodulatory capacity of the probiotic Lactobacillus gasseri OLL2809 cell-free supernatant (sup) was investigated in murine bone marrow-derived dendritic cells (DCs). Bacteria induced significantly higher expression of all examined cytokines than those induced by the stimulatory lipolysaccharide (LPS) itself. On the contrary, sup only induced the anti-inflammatory IL-10 similarly to LPS, whereas IL-12 and IL-6 secretions were stimulated at a lower level. Moreover, sup reduced the surface expression of the analysed co-stimulatory markers CD40, CD80 and CD86. Treatments of sup with different digestive enzymes indicated the proteinaceus nature of these immunomodulatory metabolites. Western blot and immunoadsorption analyses revealed cross-reactivity of sup with the surface layers proteins (SLPs) isolated from OLL2809. Therefore, we directly tested the ability of OLL2809 SLPs to stimulate specifically cytokine expression in iDCs. Interestingly, we found that all tested cytokines were induced by SLPs and in a dose-dependent manner. In conclusion, our results highlighted distinct immune properties between L. gasseri OLL2809 and its metabolites, supporting the concept that bacterial viability is not an essential prerequisite to exert immunomodulatory effects.