Abstract
- Background
Interleukin-12 is an important cytokine for the immunomodulatory effects of lactic acid bacteria. Previous research demonstrated that the RNA of Enterococcus faecalis EC-12 acts as a major interleukin-12-inducing immunogenic component in murine immune cells. However, because Toll-like receptor 13—a known ligand for bacterial RNA—is expressed exclusively in mice and absent in humans, the immunostimulatory and immunomodulatory mechanisms of bacterial RNA in human cells require evaluation independent of Toll-like receptor 13 contribution.
- Methods
This study investigated the role of lactic acid bacteria RNA in inducing interleukin-12 production across human immune cells using three strains: Enterococcus faecalis EC-12, Lactobacillus gasseri JCM5344, and Bifidobacterium breve JCM1192. Heat-killed bacteria treated with ribonuclease A or ribonuclease III were used to stimulate human peripheral blood mononuclear cells and monocyte-depleted cultures. Furthermore, using THP-1 human monocytic cells, the specific receptors mediating single-stranded RNA recognition were identified via small interfering RNA knockdown of Toll-like receptors 7 and 8, and fractionated ribosomal and messenger ribonucleic acid components were evaluated.
- Results
Ribonuclease A treatment of heat-killed lactic acid bacteria significantly decreased interleukin-12 production from human peripheral blood mononuclear cells, whereas ribonuclease III treatment had virtually no effect, and monocyte depletion abolished the response to Enterococcus faecalis EC-12. In human monocytic cells, interleukin-12 production induced by total bacterial RNA was significantly reduced by small interfering RNA targeting Toll-like receptor 8, but not Toll-like receptor 7. Additionally, both 23S and 16S ribosomal ribonucleic acid molecules of Enterococcus faecalis EC-12 markedly induced interleukin-12 production, whereas messenger ribonucleic acid did not.
- Conclusions
Single-stranded ribonucleic acid of lactic acid bacteria is a strong inducer of interleukin-12 production from human monocytes. Specifically, the recognition of Enterococcus faecalis EC-12 single-stranded ribonucleic acid is mediated by Toll-like receptor 8, with ribosomal ribonucleic acid identified as the primary active macromolecule responsible for interleukin-12-inducing activity in human cells.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4470910/