Specific Lactobacillus species differentially activate Toll-like receptors and downstream signals in dendritic cells

Background: Dendritic cells (DCs) regulate mucosal T-cell immunity and encounter several distinct bacteria of the gut flora, including lactobacilli. Gram-positive lactobacilli have been suggested to play an important role in exerting adjuvanticity effects on innate immune cells at mucosal sites. Aims & methods: In the present report, we studied the effects of specific Lactobacillus species on human monocyte derived DCs. Results: We show that lactobacilli activate DCs by differentially inducing the expression of Toll-like receptors and bioactive IL-12 in Lactobacillus-treated DCs. Further, these specific Lactobacillus spp. did not activate the phosphorylation of p38 MAK, which might be a downstream effect of the remarkable capacity of lactobacilli to induce IL-12 in DCs that skew T cells significantly toward an IFN-gamma-secreting Th1 response. Conclusion: These results highlight an important role of specific Lactobacillus spp. as adjuvants in triggering DC function, which in turn may determine the immunological outcome in an environment wherein innate cells reside.