Polyinosinic Acid Is a Ligand for Toll-like Receptor 3

Stuart Marshall-Clarke,Joan E Downes,Ismar R Haga,Andrew G Bowie,Persephone Borrow,Joanne L Pennock,Richard K Grencis,Paul Rothwell

doi:10.1074/jbc.m700188200

Abstract

Innate immune responses are critical in controlling viral infections. Viral proteins and nucleic acids have been shown to be recognized by pattern recognition receptors of the Toll-like receptor (TLR) family, triggering downstream signaling cascades that lead to cellular activation and cytokine production. Viral DNA is sensed by TLR9, and TLRs 3, 7, and 8 have been implicated in innate responses to RNA viruses by virtue of their ability to sense double-stranded (ds) RNA (TLR3) or single-stranded RNA (murine TLR7 and human TLR8). Viral and synthetic dsRNAs have also been shown to be a potent adjuvant, promoting enhanced adaptive immune responses, and this property is also dependent on their recognition by TLR3. It has recently been shown that mRNA that is largely single-stranded is a ligand for TLR3. Here we have investigated the ability of single-stranded homopolymeric nucleic acids to induce innate responses by murine immune cells. We show for the first time that polyinosinic acid (poly(I)) activates B lymphocytes, dendritic cells, and macrophages and that these responses are dependent on the expression of both TLR3 and the adaptor molecule, Toll/IL-1 receptor domain-containing adaptor inducing IFN-beta (TRIF). We therefore conclude that TLR3 is able to sense both single-stranded RNA and dsRNA.

Highlights

Double-stranded RNA can be detected by TLR3 [9] and by intracellular pattern recognition receptors belonging to the retinoic acid-inducible protein (RIG)-like helicase family, and these molecules have been found to be important for effective viral immunity [6, 10, 11]
Purified influenza genomic RNA and the synthetic homopolymer polyuridylic acid (poly(U)) (but not poly(A), poly(C), poly(G), or poly(I)) were shown to elicit IFN-␣ when transfected into plasmacytoid dendritic cells (DCs) from wild type but not TLR7-deficient mice [12], and GU-rich oligonucleotides derived from an human immunodeficiency virus RNA sequence elicited TLR8-dependent innate responses when transfected into human DC [13]
The data show that responses to both poly(I:C) and Recognition of microbial nucleic acids is an important funcpoly(I) were exclusively dependent on the Toll/IL-1 receptor domain-containing adaptor inducing IFN-␤ (TRIF) adaptor and tion of the innate immune system, playing a critical role in prothose induced by the TLR9 ligand were exclusively dependent tection against viral infection

Summary

Introduction

We assessed the effects of homopolymeric nucleic acids on B cells by culturing them with poly(I), poly (U), or known ligands for TLRs 3 and 4 and analyzing the expression of co-stimulatory molecules. The data show cells (BMDC) and macrophages to poly(I), poly(U), and TLR that induction of up-regulation of co-stimulatory molecules ligands. Double-stranded poly(I:C) The responses of BMDC from MyD88- and TLR4-deficient is a classical inducer of the production of type 1 interferons.

Results

Conclusion