Cell-specific IRF-3 responses protect against West Nile virus infection by interferon-dependent and -independent mechanisms - PubMed (original) (raw)
Cell-specific IRF-3 responses protect against West Nile virus infection by interferon-dependent and -independent mechanisms
Stephane Daffis et al. PLoS Pathog. 2007.
Abstract
Interferon regulatory factor (IRF)-3 is a master transcription factor that activates host antiviral defense programs. Although cell culture studies suggest that IRF-3 promotes antiviral control by inducing interferon (IFN)-beta, near normal levels of IFN-alpha and IFN-beta were observed in IRF-3(-/-) mice after infection by several RNA and DNA viruses. Thus, the specific mechanisms by which IRF-3 modulates viral infection remain controversial. Some of this disparity could reflect direct IRF-3-dependent antiviral responses in specific cell types to control infection. To address this and determine how IRF-3 coordinates an antiviral response, we infected IRF-3(-/-) mice and two primary cells relevant for West Nile virus (WNV) pathogenesis, macrophages and cortical neurons. IRF-3(-/-) mice were uniformly vulnerable to infection and developed elevated WNV burdens in peripheral and central nervous system tissues, though peripheral IFN responses were largely normal. Whereas wild-type macrophages basally expressed key host defense molecules, including RIG-I, MDA5, ISG54, and ISG56, and restricted WNV infection, IRF-3(-/-) macrophages lacked basal expression of these host defense genes and supported increased WNV infection and IFN-alpha and IFN-beta production. In contrast, wild-type cortical neurons were highly permissive to WNV and did not basally express RIG-I, MDA5, ISG54, and ISG56. IRF-3(-/-) neurons lacked induction of host defense genes and had blunted IFN-alpha and IFN-beta production, yet exhibited only modestly increased viral titers. Collectively, our data suggest that cell-specific IRF-3 responses protect against WNV infection through both IFN-dependent and -independent programs.
Conflict of interest statement
Competing interests. The authors have declared that no competing interests exist.
Figures
Figure 1. Survival and Virologic Analysis for Wild-Type and IRF-3−/− C57BL/6 Mice
(A) Eight- to twelve-week-old mice were inoculated with 102 PFU of WNV by footpad injection and followed for mortality for 21 d. Survival differences were statistically significant (n = 20, IRF-3−/−; and n = 20, wild-type mice; p < 0.0001). (B–G) Viral burden in peripheral and CNS tissues after WNV infection. WNV RNA in (B) serum and (C) draining lymph node, and infectious virus in the (D) spleen, (E) kidney, (F) brain, and (G) spinal cord were determined from samples harvested on days 1, 2, 4, 6, 8, and 10 using qRT-PCR (B, C) or viral plaque assay (D–G). Data is shown as viral RNA equivalents or PFU per gram of tissue for ten to 12 mice per time point. For all viral load data, the solid line represents the median PFU per gram at the indicated time point, and the dotted line represents the limit of sensitivity of the assay. Error bars indicate the standard deviations (SD). Asterisks indicate values that are statistically significant (*, p < 0.05; **, p < 0.005; ***, p < 0.0001) compared to wild-type mice.
Figure 2. IFN Induction in Draining Lymph Nodes and Serum of Mice Infected with WNV
(A, B) Mice were inoculated with 102 PFU of WNV by footpad injection and euthanized at the indicated times. Total RNA from draining lymph was analyzed for (A) IFN-α and (B) IFN-β mRNA expression by qRT-PCR. Data are normalized to 18S rRNA and are expressed as the relative fold increase over normalized RNA from uninfected controls. Average values are from five to 12 mice per time point, and error bars indicate the SD. Asterisks indicate differences that are statistically significant (*, p < 0.05). (C) IFN activity was determined from serum collected on days 1 to 4 after infection by an EMCV bioassay in L929 cells. Data reflect the average of serum samples harvested from five to ten mice per time point and are shown as the percentage of cells protected from lysis by EMCV (see Materials and Methods). Asterisks indicate differences that are statistically significant (*, p < 0.05; ***, p < 0.0001).
Figure 3. IRF-3 Modulates WNV Infection in Primary Macrophages
(A) Macrophages generated from wild-type or IRF-3−/− mice were infected at an MOI of 0.01, and virus production was evaluated at the indicated times post infection by plaque assay. Values are an average of quadruplicate samples generated from at least three independent experiments. Error bars represent the SD, and asterisks indicate differences that are statistically significant relative to wild-type mice (*, p < 0.05; **, p < 0.005; ***, p < 0.0001). (B) The induction of IFN-α and IFN-β mRNA in WNV-infected macrophages was analyzed by qRT-PCR as described in Figure 2. (C, D) Accumulation of IFN-α (C) and IFN-β (D) protein in supernatants of WNV-infected macrophages was determined by ELISA. The data is the average of at least five independent experiments performed in triplicate. *, p < 0.05. (E) The induction of IRF-7 mRNA in WNV-infected macrophages was analyzed by qRT-PCR as described in Figure 2. *, p < 0.05.
Figure 4. The Effect of IRF-3 on ISG54, ISG56, RIG-I, and MDA5 Expression in Macrophages
(A) Whole cell lysates were generated at the indicated times from wild-type or IRF-3−/− macrophages that were uninfected (U), infected with WNV (W), or pretreated with 100 IU/ml of IFN-β (Pre). Protein levels of ISG54 and GAPDH were examined by immunoblot analysis. (B) Total RNA was harvested from WNV-infected macrophages and mRNA levels of ISG56 were quantified by qRT-PCR as described in Figure 2. Data are expressed as relative fold induction over uninfected IRF-3−/− cells. Asterisks indicate differences that are statistically significant (**, p < 0.005). (C) Whole cell lysates were generated at the indicated times from wild-type or IRF-3−/− macrophages that were uninfected (U) or infected with WNV (W) for 12 or 24 h. Protein levels of RIG-I, MDA5, and GAPDH were examined by immunoblot analysis
Figure 5. WNV Infection and IFN Production in Primary Cortical Neurons
(A) Primary cortical neurons generated from wild-type or IRF-3−/− mice were infected at an MOI of 0.001, and virus production was evaluated at the indicated times by plaque assay. Values are an average of triplicate samples generated from three independent experiments, error bars represent the SD, and asterisks indicate values that are statistically significant (**, p < 0.005). (B–D) The induction of IFN-α and IFN-β mRNA in WNV-infected primary cortical neurons. IFN mRNA was analyzed by qRT-PCR as described in Figure 2. (C) IFN-α and (D) IFN-β protein accumulation in supernatants of WNV-infected cortical neurons from wild-type and IRF-3−/− mice was measured by ELISA. (E) The induction of IRF-7 mRNA in WNV-infected primary cortical neurons was analyzed by qRT-PCR as described in Figure 2. (B–E) Data are the average of three independent experiments performed in duplicate, and the asterisks indicate statistically significant differences (*, p < 0.05; **, p < 0.005, ***, p < 0.0001).
Figure 6. The Effect of IRF-3 on ISG54, ISG56, RIG-I, and MDA5 Expression in WNV-Infected Cortical Neurons
(A, B) Whole cell lysates were generated at the indicated times from wild-type or IRF-3−/− primary cortical neurons. These neurons were uninfected (U), infected with WNV (W), pretreated with 100 IU/ml of IFN-β (Pre), or treated with IFN after infection (P/W). (A) ISG54 immunoblot analysis and figure labeling is as described in Figure 4. (B) Protein levels of IRF-3, RIG-I, MDA5, ISG56, WNV, and GAPDH were examined by immunoblot analysis as described in Materials and Methods.
References
- Byrne SN, Halliday GM, Johnston LJ, King NJ. Interleukin-1beta but not tumor necrosis factor is involved in West Nile virus-induced Langerhans cell migration from the skin in C57BL/6 mice. J Invest Dermatol. 2001;117:702–709. - PubMed
- Johnston LJ, Halliday GM, King NJ. Langerhans cells migrate to local lymph nodes following cutaneous infection with an arbovirus. J Invest Dermatol. 2000;114:560–568. - PubMed
- Guarner J, Shieh WJ, Hunter S, Paddock CD, Morken T, et al. Clinicopathologic study and laboratory diagnosis of 23 cases with West Nile virus encephalomyelitis. Hum Pathol. 2004;35:983–990. - PubMed
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