RNA of Enterococcus faecalis Strain EC-12 Is a Major Component Inducing Interleukin-12 Production from Human Monocytic Cells.

Ryoichiro Nishibayashi,Ryo Inoue,Yuri Harada,Kazunari Ushida,Takumi Watanabe,Yuko Makioka,Dipshikha Chakravortty

doi:10.1371/journal.pone.0129806

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.

Highlights

Various effects of lactic acid bacteria (LAB) that are beneficial to health, such as antitumor [1, 2], anti-allergy [3, 4], and anti-infectious effects [5, 6], have been demonstrated in both human and animal models
In experiment 1, we evaluated the role of the cell wall, DNA, and RNA of three LAB strains, E.faecalis EC-12, Lactobacillus gasseri JCM5344, and Bifidobacterium breve JCM1192, in inducing IL-12 production from human immune cells
This study clearly demonstrated that single stranded RNA (ssRNA) of EC-12 and at least two other LAB strains evaluated was an important immunogenic component for IL-12 production from human immune cells

Summary

Introduction

Various effects of lactic acid bacteria (LAB) that are beneficial to health, such as antitumor [1, 2], anti-allergy [3, 4], and anti-infectious effects [5, 6], have been demonstrated in both human and animal models. Recent evidence from in vivo studies has suggested that live and heat-killed LAB exert many of the above-mentioned beneficial effects [8,9,10,11,12]. It is suggested that the effects of heat-killed LAB are derived from immunomodulation rather than alteration of the intestinal microbiota. Many studies have focused on the immunogenic components of LAB using both mouse and human immune cells [13,14,15,16]

Objectives

Results

Conclusion