Duck MDA5 functions in innate immunity against H5N1 highly pathogenic avian influenza virus infections.

Liangmeng Wei,Peirong Jiao,Ming Liao,Yafen Song,Jin Cui,Shuo Zhang,Fei Han,Runyu Yuan,Lang Gong

doi:10.1186/1297-9716-45-66

Abstract

Melanoma differentiation-associated gene 5 (MDA5) is an important intracellular receptor that recognizes long molecules of viral double-stranded RNA in innate immunity. To understand the mechanism of duck MDA5-mediated innate immunity, we cloned the MDA5 cDNA from the Muscovy duck (Cairina moschata). Quantitative real-time PCR analysis indicates that duck MDA5 mRNA was constitutively expressed in all sampled tissues. A significant increase of MDA5 mRNA was detected in the brain, spleen and lungs of ducks after infection with an H5N1 highly pathogenic avian influenza virus (HPAIV). We investigated the role of the predicted functional domains of MDA5. The results indicate the caspase activation and recruitment domain (CARD) of duck MDA5 had a signal transmission function through IRF-7-dependent signaling pathway. Overexpression of the CARD strongly activated the chicken IFN-β promoter and upregulated the mRNA expression of antiviral molecules (such as OAS, PKR and Mx), proinflammatory cytokines (such as IL-2, IL-6, IFN-α and IFN-γ, but not IL-1β and IL-8) and retinoic acid-inducible gene I (RIG-I)-like receptors (RLR) (RIG-I and LGP2) without exogenous stimulation. We also demonstrate the NS1 of the H5N1 HPAIV inhibited the duck MDA5-mediated signaling pathway in vitro. These results suggest that duck MDA5 is an important receptor for inducing antiviral activity in the host immune response of ducks.

Highlights

The innate immune system is an evolutionarily conserved system that protects the host from invading microbial pathogens and other potential threats through germline-encoded pattern recognition receptors [1]
Overexpression of the caspase activation and recruitment domains (CARD) of duck melanoma differentiation-associated gene 5 (MDA5) significantly induced the chicken IFN-β (chIFN-β) promoter, which is consistent with the function of MDA5 in mammalian systems [33,34]
Overexpression of the Muscovy duck MDA5 lacking the CARD failed to induce the chIFN-β promoter (Figure 3). These results demonstrate the CARD of Muscovy duck MDA5 has a similar function as its counterpart in mammals, which is involved in immune signaling [4,5,30]

Summary

Introduction

The innate immune system ( known as the non-specific immune system) is an evolutionarily conserved system that protects the host from invading microbial pathogens and other potential threats through germline-encoded pattern recognition receptors [1]. Pattern recognition receptors are located on multiple types of innate immune cells and are capable of responding to specific pathogen associated molecular patterns exclusively present on microbes, such as viruses, bacteria, parasites and fungi. Some pattern recognition receptors such as toll-like receptors (TLRs; e.g., TLR-3, -7, -8 and -9), retinoic acid-inducible gene I (RIG-I)-like receptors (RLR) and nucleotide oligomerization domain-like receptors are activated, which recognize various types of viral nucleotides [1,2]. The RLR family contains three members: RIG-I, melanoma differentiation-associated gene 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2), which are located in the cytoplasm [3]. MDA5 senses longer dsRNA (>1 kb) and synthetic dsRNA, such as polyinosinicpolycytidylic acid (poly [I:C]) [8]

Methods

Results

Conclusion