title: RNA of Enterococcus faecalis Strain EC-12 Is a Major Component Inducing Interleukin-12 Production from Human Monocytic Cells.
abstract: Interleukin-12 (IL-12) is an important cytokine for the immunomodulatory effects of lactic acid bacteria (LAB). Using murine immune cells, we previously reported that the RNA of Enterococcus faecalis EC-12, a LAB strain exerting probiotic-like beneficial effects, is the major IL-12-inducing immunogenic component. However, it was recently revealed that bacterial RNA can be a ligand for Toll-like receptor (TLR) 13, which is only expressed in mice. Because TLR13 is not expressed in humans, the immuno-stimulatory and -modulatory effects of LAB RNA in human cells should be augmented excluding TLR13 contribution. In experiment 1 of this study, the role of LAB RNA in IL-12 induction in human immune cells was studied using three LAB strains, E.faecalis EC-12, Lactobacillus gasseri JCM5344, and Bifidobacterium breve JCM1192. RNase A treatment of heat-killed LAB significantly decreased the IL-12 production of human peripheral blood mononuclear cells on stimulation, while RNase III treatment revealed virtually no effects. Further, IL-12 production against heat-killed E. faecalis EC-12 was abolished by depleting monocytes. These results demonstrated that single stranded RNA (ssRNA) of LAB is a strong inducer of IL-12 production from human monocytes. In experiment 2, major receptor for ssRNA of E. faecalis EC-12 was identified using THP-1 cells, a human monocytic cell line. The type of RNA molecules of E. faecalis EC-12 responsible for IL-12 induction was also identified. IL-12 production induced by the total RNA of E. faecalis EC-12 was significantly reduced by the treatment of siRNA for TLR8 but not for TLR7. Furthermore, both 23S and 16S rRNA, but not mRNA, of E. faecalis EC-12 markedly induced IL-12 production from THP-1 cells. These results suggested that the recognition of ssRNA of E. faecalis EC-12 was mediated by TLR8 and that rRNA was the RNA molecule that exhibited IL-12-inducing ability in human cells.
authors.affiliation: Laboratory of Animal Science, Kyoto Prefectural University, Kyoto, Kyoto, Japan.
authors.forename: Ryoichiro
authors.initials: R
authors.lastname: Nishibayashi
authors.affiliation: Laboratory of Animal Science, Kyoto Prefectural University, Kyoto, Kyoto, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Inoue
authors.affiliation: Laboratory of Animal Science, Kyoto Prefectural University, Kyoto, Kyoto, Japan.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Harada
authors.affiliation: Department of Functional Foods, Combi Corporation, Saitama, Saitama, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: Department of Functional Foods, Combi Corporation, Saitama, Saitama, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Makioka
authors.affiliation: Laboratory of Animal Science, Kyoto Prefectural University, Kyoto, Kyoto, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Ushida
mesh_terms: D002478:Cells, Cultured; D013293:Enterococcus faecalis / Q000276:immunology*; D016908:Gram-Positive Bacterial Infections / Q000276:immunology* / Q000382:microbiology; D006801:Humans; D018664:Interleukin-12 / Q000276:immunology*; D007963:Leukocytes, Mononuclear / Q000276:immunology / Q000382:microbiology; D009000:Monocytes / Q000276:immunology / Q000382:microbiology*; D012329:RNA, Bacterial / Q000276:immunology*
chemical_list: D012329:RNA, Bacterial; D018664:Interleukin-12