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, 6 (1), e1000734

Melanoma Differentiation-Associated Gene 5 (MDA5) Is Involved in the Innate Immune Response to Paramyxoviridae Infection in Vivo

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Melanoma Differentiation-Associated Gene 5 (MDA5) Is Involved in the Innate Immune Response to Paramyxoviridae Infection in Vivo

Leonid Gitlin et al. PLoS Pathog.

Abstract

The early host response to pathogens is mediated by several distinct pattern recognition receptors. Cytoplasmic RNA helicases including RIG-I and MDA5 have been shown to respond to viral RNA by inducing interferon (IFN) production. Previous in vitro studies have demonstrated a direct role for MDA5 in the response to members of the Picornaviridae, Flaviviridae and Caliciviridae virus families ((+) ssRNA viruses) but not to Paramyxoviridae or Orthomyxoviridae ((-) ssRNA viruses). Contrary to these findings, we now show that MDA5 responds critically to infections caused by Paramyxoviridae in vivo. Using an established model of natural Sendai virus (SeV) infection, we demonstrate that MDA5(-/-) mice exhibit increased morbidity and mortality as well as severe histopathological changes in the lower airways in response to SeV. Moreover, analysis of viral propagation in the lungs of MDA5(-/-) mice reveals enhanced replication and a distinct distribution involving the interstitium. Though the levels of antiviral cytokines were comparable early during SeV infection, type I, II, and III IFN mRNA expression profiles were significantly decreased in MDA5(-/-) mice by day 5 post infection. Taken together, these findings indicate that MDA5 is indispensable for sustained expression of IFN in response to paramyxovirus infection and provide the first evidence of MDA5-dependent containment of in vivo infections caused by (-) sense RNA viruses.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Infection with SeV causes increased morbidity and mortality in MDA5−/− mice.
WT and MDA5−/− mice were infected with 200K pfu SeV and assessed for A) loss of body weight over the PI period and B) mucus production (PAS reactivity). C) WT and MDA5−/− mice were infected with 200K, 400K and 600K pfu SeV and assessed for viability. N = 4–16 mice, error bars refer to SEM, * P≤0.05.
Figure 2
Figure 2. Increased histopathology in MDA5−/− mice.
A) H&E micrographs of lung sections obtained from WT and MDA5−/− mice infected with 400K pfu SeV on d5, d9, d12 PI. B) FACS analysis of lymphocytes derived from the lungs of WT and MDA5−/− mice, uninfected (top panels) and d5 post infected (bottom panels) stained with anti-CD8 and H-2Kb: FAPGNYPAL pentamer.
Figure 3
Figure 3. SeV replication is enhanced in MDA5−/− mice.
WT and MDA5−/− mice infected with 200K pfu SeV were assessed for A) SeV replication by IF detection of SeV antigens and by real time PCR analysis of B) SeV genome and C) SeV N gene expression. N = 4, error bars refer to SEM, * P<0.05; ** P<0.005.
Figure 4
Figure 4. MDA5 is required for sustained expression of cytokines in response to SeV infection.
Real time PCR analysis of whole lung homogenates obtained from WT and MDA5−/− mice infected with 200K pfu SeV for expression levels of A) Ifn-α2, B) Ifn-β, C) Ifn-γ, D) Il-28b, E) Tnf-α, F) Il-1β, G) Il-6 and H) Il-10 mRNA. N = 4, error bars refer to SEM, * P<0.05, ** P<0.00001.
Figure 5
Figure 5. Infection with SeV results in induction of antiviral sensor expression.
A) Analysis of Mda5 and Rig-I mRNA expression in WT mice during the acute SeV infection period as determined by real-time PCR analysis. B) Micrographs taken of lung sections obtained from WT and MDA5−/− mice infected with 200K pfu SeV and stained for MDA5 expression. N = 4, error bars refer to SEM, * P<0.05.

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