Lactobacillus acidophilus induces virus immune defense genes in murine dendritic cells by a TLR-2 dependent mechanism

Lactobacilli are probiotics that, among other health promoting effects, have been ascribed immunostimulating and virus preventive properties. Certain lactobacilli species have been shown to possess strong IL-12 inducing properties. As IL-12 production depends on the up-regulation of type I interferons, we hypothesized that the strong IL-12 inducing capacity of L. acidophilus NCFM in murine bone marrow derived DC is caused by an up-regulation of IFN-β, which subsequently stimulates the induction of IL-12 and the dsRNA binding toll like receptor (TLR)-3. The expression of the genes encoding IFN-β, IL-12, IL-10 and TLR-3 in DC upon stimulation with L. acidophilus NCFM was measured. L. acidophilus NCFM induced a much stronger expression of ifn-β, il-12 and il-10 compared to the synthetic dsRNA ligand Poly I:C, whereas the levels of expressed tlr-3 were similar. By the use of whole genome microarray gene expression, we investigated whether other genes related to the viral defence were up-regulated in DC upon stimulation with L. acidophilus NCFM and found that various virus defence related genes, both early and late, were among the strongest up-regulated genes. The IFN-β stimulating capability was also detected in another L. acidophilus strain, but was not a property of other probiotic bacteria tested (B. bifidum and E. coli nissle).The IFN-β inducing capacity was markedly reduced in TLR-2 -/- DCs, dependent on endocytosis and the major cause of the induction of il-12 and tlr-3 in L. acidophilus NCFM stimulated cells. Collectively, our results reveal that certain lactobacilli trigger the expression of viral defence genes in DC in a TLR-2 manner through induction of IFN- β. In the experiment Lactobacillus NCFM were added to murine dendritic cells and stimulated for 4, 10 or 18 hours. These were compared to control experiment at the same timepoints. Experiments were run in triplicates except for control 10h and control 18h which were only in duplicate, giving a total of 16 arrays.