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STAT2 mediates innate immunity to Dengue virus in the absence of STAT1 via the type I interferon receptor.

Perry ST, Buck MD, Lada SM, Schindler C, Shresta S - PLoS Pathog. (2011)

Bottom Line: High viral loads correlate with disease severity, and both type I & II interferons (IFNs) are crucial for controlling viral replication.Further studies demonstrated that this STAT2-dependent STAT1-independent mechanism requires the type I IFN receptor, and contributes to the autocrine amplification of type I IFN expression.Examination of gene expression in the spleen and bone marrow-derived macrophages following DENV infection revealed STAT2-dependent pathways can induce the transcription of a subset of interferon stimulated genes even in the absence of STAT1.

View Article: PubMed Central - PubMed

Affiliation: Division of Vaccine Discovery, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.

ABSTRACT
Dengue virus (DENV) is a mosquito-borne flavivirus, and symptoms of infection range from asymptomatic to the severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). High viral loads correlate with disease severity, and both type I & II interferons (IFNs) are crucial for controlling viral replication. We have previously reported that signal transducer and activator of transcription (STAT) 1-deficient mice are resistant to DENV-induced disease, but little is known about this STAT1-independent mechanism of protection. To determine the molecular basis of the STAT1-independent pathway, mice lacking STAT1, STAT2, or both STAT1 and STAT2 were infected with a virulent mouse-adapted strain of DENV2. In the first 72 hours of infection, the single-deficient mice lacking STAT1 or STAT2 possessed 50-100 fold higher levels of viral RNA than wild type mice in the serum, spleen, and other visceral tissues, but remained resistant to DENV-induced death. In contrast, the double-deficient mice exhibited the early death phenotype previously observed in type I and II IFN receptor knockout mice (AG129), indicating that STAT2 is the mediator of the STAT1-independent host defense mechanism. Further studies demonstrated that this STAT2-dependent STAT1-independent mechanism requires the type I IFN receptor, and contributes to the autocrine amplification of type I IFN expression. Examination of gene expression in the spleen and bone marrow-derived macrophages following DENV infection revealed STAT2-dependent pathways can induce the transcription of a subset of interferon stimulated genes even in the absence of STAT1. Collectively, these results help elucidate the nature of the poorly understood STAT1-independent host defense mechanism against viruses by identifying a functional type I IFN/STAT2 signaling pathway following DENV infection in vivo.

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Viral RNA levels in DENV-infected mice.Mice were infected i.v. with 1010 GE of S221. (A–C) Quantification of DENV RNA in the (A) serum and (B) spleen at 6, 12, 18, 24 and 72 hours post-infection, and (C) liver, kidney, and small intestine at 72 hours post-infection as determined by quantitative RT-PCR (6h n = 4; 12h n = 8; 18h n = 8; 24h n = 12; 72h n = 4). Data are shown as GE per mL of serum or GE per copy of 18S RNA for tissues. The dotted line represents the limit of detection of the assay for each tissue. (D) Levels of TNF in the serum of DENV-infected mice at 72 hours post-infection (n = 7 per group). Error bars represent the SEM and asterisks denote statistically significant differences (*, p<0.05; **, p<0.005; ***, p<0.0005; ns = not significant). Results are representative of two independent experiments.
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ppat-1001297-g002: Viral RNA levels in DENV-infected mice.Mice were infected i.v. with 1010 GE of S221. (A–C) Quantification of DENV RNA in the (A) serum and (B) spleen at 6, 12, 18, 24 and 72 hours post-infection, and (C) liver, kidney, and small intestine at 72 hours post-infection as determined by quantitative RT-PCR (6h n = 4; 12h n = 8; 18h n = 8; 24h n = 12; 72h n = 4). Data are shown as GE per mL of serum or GE per copy of 18S RNA for tissues. The dotted line represents the limit of detection of the assay for each tissue. (D) Levels of TNF in the serum of DENV-infected mice at 72 hours post-infection (n = 7 per group). Error bars represent the SEM and asterisks denote statistically significant differences (*, p<0.05; **, p<0.005; ***, p<0.0005; ns = not significant). Results are representative of two independent experiments.

Mentions: To evaluate how STAT1 and STAT2 deficiency impacts the control of DENV infection, wild type, STAT1−/−, STAT2−/−, STAT1−/−/2−/−, and STAT1−/−/AR−/− mice were infected intravenously with 1010 GE of S221, and viral RNA levels in various tissues were measured via qRT-PCR at 6, 12, 18, 24, and 72 hours after infection. Although minimal viral RNA was detected in each strain at 6 hours post-infection, increasing viremia was observed in all strains except wild type by 12 hours post-infection. At 12, 18, and 24 hours post-infection, the high viremia observed in the single- and double-deficient strains (all p<0.0005) demonstrates that the combined function of both STAT1 and STAT2 is required for effective control of viral replication (Figure 2A). Previous studies have shown that the spleen is an initial site of DENV replication in mice [28], [34], and at 18 and 24 hours post-infection, levels of DENV RNA in the spleen of each knockout mouse strain were significantly higher than wild type (14- to 27-fold increase; all p<0.0005) (Figure 2B). Although each single-deficient mouse strain possessed similar levels of viral RNA as STAT1−/−/2−/− mice at 12 and 18 hours post-infection, the levels of virus in the serum and spleen were 6–7 fold higher in STAT1−/− mice than STAT2−/− mice by 24 hours. This suggests that early control of DENV replication requires the combined function of STAT1 and STAT2, but STAT2-independent mechanism(s) begin to restrict replication by 24 hours post-infection. At 72 hours post-infection, viremia in both STAT1−/− and STAT2−/− mice was reduced relative to the 24-hour time point (STAT1−/− 30-fold, p<0.0001; STAT2−/− 33-fold, p = 0.0019), and the levels of viremia were similar between these two strains. In contrast to the single-deficient mice, viremia in STAT1−/−/2−/− mice increased 25-fold between 24 and 72 hours after infection. By 72 hours, viral RNA levels in the spleen had decreased significantly in all mouse strains, but remained at least 40-fold higher in STAT1−/−/2−/− mice as compared to the single-deficient strains.


STAT2 mediates innate immunity to Dengue virus in the absence of STAT1 via the type I interferon receptor.

Perry ST, Buck MD, Lada SM, Schindler C, Shresta S - PLoS Pathog. (2011)

Viral RNA levels in DENV-infected mice.Mice were infected i.v. with 1010 GE of S221. (A–C) Quantification of DENV RNA in the (A) serum and (B) spleen at 6, 12, 18, 24 and 72 hours post-infection, and (C) liver, kidney, and small intestine at 72 hours post-infection as determined by quantitative RT-PCR (6h n = 4; 12h n = 8; 18h n = 8; 24h n = 12; 72h n = 4). Data are shown as GE per mL of serum or GE per copy of 18S RNA for tissues. The dotted line represents the limit of detection of the assay for each tissue. (D) Levels of TNF in the serum of DENV-infected mice at 72 hours post-infection (n = 7 per group). Error bars represent the SEM and asterisks denote statistically significant differences (*, p<0.05; **, p<0.005; ***, p<0.0005; ns = not significant). Results are representative of two independent experiments.
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getmorefigures.php?uid=PMC3040673&req=5

ppat-1001297-g002: Viral RNA levels in DENV-infected mice.Mice were infected i.v. with 1010 GE of S221. (A–C) Quantification of DENV RNA in the (A) serum and (B) spleen at 6, 12, 18, 24 and 72 hours post-infection, and (C) liver, kidney, and small intestine at 72 hours post-infection as determined by quantitative RT-PCR (6h n = 4; 12h n = 8; 18h n = 8; 24h n = 12; 72h n = 4). Data are shown as GE per mL of serum or GE per copy of 18S RNA for tissues. The dotted line represents the limit of detection of the assay for each tissue. (D) Levels of TNF in the serum of DENV-infected mice at 72 hours post-infection (n = 7 per group). Error bars represent the SEM and asterisks denote statistically significant differences (*, p<0.05; **, p<0.005; ***, p<0.0005; ns = not significant). Results are representative of two independent experiments.
Mentions: To evaluate how STAT1 and STAT2 deficiency impacts the control of DENV infection, wild type, STAT1−/−, STAT2−/−, STAT1−/−/2−/−, and STAT1−/−/AR−/− mice were infected intravenously with 1010 GE of S221, and viral RNA levels in various tissues were measured via qRT-PCR at 6, 12, 18, 24, and 72 hours after infection. Although minimal viral RNA was detected in each strain at 6 hours post-infection, increasing viremia was observed in all strains except wild type by 12 hours post-infection. At 12, 18, and 24 hours post-infection, the high viremia observed in the single- and double-deficient strains (all p<0.0005) demonstrates that the combined function of both STAT1 and STAT2 is required for effective control of viral replication (Figure 2A). Previous studies have shown that the spleen is an initial site of DENV replication in mice [28], [34], and at 18 and 24 hours post-infection, levels of DENV RNA in the spleen of each knockout mouse strain were significantly higher than wild type (14- to 27-fold increase; all p<0.0005) (Figure 2B). Although each single-deficient mouse strain possessed similar levels of viral RNA as STAT1−/−/2−/− mice at 12 and 18 hours post-infection, the levels of virus in the serum and spleen were 6–7 fold higher in STAT1−/− mice than STAT2−/− mice by 24 hours. This suggests that early control of DENV replication requires the combined function of STAT1 and STAT2, but STAT2-independent mechanism(s) begin to restrict replication by 24 hours post-infection. At 72 hours post-infection, viremia in both STAT1−/− and STAT2−/− mice was reduced relative to the 24-hour time point (STAT1−/− 30-fold, p<0.0001; STAT2−/− 33-fold, p = 0.0019), and the levels of viremia were similar between these two strains. In contrast to the single-deficient mice, viremia in STAT1−/−/2−/− mice increased 25-fold between 24 and 72 hours after infection. By 72 hours, viral RNA levels in the spleen had decreased significantly in all mouse strains, but remained at least 40-fold higher in STAT1−/−/2−/− mice as compared to the single-deficient strains.

Bottom Line: High viral loads correlate with disease severity, and both type I & II interferons (IFNs) are crucial for controlling viral replication.Further studies demonstrated that this STAT2-dependent STAT1-independent mechanism requires the type I IFN receptor, and contributes to the autocrine amplification of type I IFN expression.Examination of gene expression in the spleen and bone marrow-derived macrophages following DENV infection revealed STAT2-dependent pathways can induce the transcription of a subset of interferon stimulated genes even in the absence of STAT1.

View Article: PubMed Central - PubMed

Affiliation: Division of Vaccine Discovery, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.

ABSTRACT
Dengue virus (DENV) is a mosquito-borne flavivirus, and symptoms of infection range from asymptomatic to the severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). High viral loads correlate with disease severity, and both type I & II interferons (IFNs) are crucial for controlling viral replication. We have previously reported that signal transducer and activator of transcription (STAT) 1-deficient mice are resistant to DENV-induced disease, but little is known about this STAT1-independent mechanism of protection. To determine the molecular basis of the STAT1-independent pathway, mice lacking STAT1, STAT2, or both STAT1 and STAT2 were infected with a virulent mouse-adapted strain of DENV2. In the first 72 hours of infection, the single-deficient mice lacking STAT1 or STAT2 possessed 50-100 fold higher levels of viral RNA than wild type mice in the serum, spleen, and other visceral tissues, but remained resistant to DENV-induced death. In contrast, the double-deficient mice exhibited the early death phenotype previously observed in type I and II IFN receptor knockout mice (AG129), indicating that STAT2 is the mediator of the STAT1-independent host defense mechanism. Further studies demonstrated that this STAT2-dependent STAT1-independent mechanism requires the type I IFN receptor, and contributes to the autocrine amplification of type I IFN expression. Examination of gene expression in the spleen and bone marrow-derived macrophages following DENV infection revealed STAT2-dependent pathways can induce the transcription of a subset of interferon stimulated genes even in the absence of STAT1. Collectively, these results help elucidate the nature of the poorly understood STAT1-independent host defense mechanism against viruses by identifying a functional type I IFN/STAT2 signaling pathway following DENV infection in vivo.

Show MeSH
Related in: MedlinePlus