Regional astrocyte IFN signaling restricts pathogenesis during neurotropic viral infection
Brian P. Daniels, Harsha Jujjavarapu, Douglas M. Durrant, Jessica L. Williams, Richard R. Green, James P. White, Helen M. Lazear, Michael Gale Jr., Michael S. Diamond, Robyn S. Klein
Brian P. Daniels, Harsha Jujjavarapu, Douglas M. Durrant, Jessica L. Williams, Richard R. Green, James P. White, Helen M. Lazear, Michael Gale Jr., Michael S. Diamond, Robyn S. Klein
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Research Article Infectious disease

Regional astrocyte IFN signaling restricts pathogenesis during neurotropic viral infection

Abstract

Type I IFNs promote cellular responses to viruses, and IFN receptor (IFNAR) signaling regulates the responses of endothelial cells of the blood-brain barrier (BBB) during neurotropic viral infection. However, the role of astrocytes in innate immune responses of the BBB during viral infection of the CNS remains to be fully elucidated. Here, we have demonstrated that type I IFNAR signaling in astrocytes regulates BBB permeability and protects the cerebellum from infection and immunopathology. Mice with astrocyte-specific loss of IFNAR signaling showed decreased survival after West Nile virus infection. Accelerated mortality was not due to expanded viral tropism or increased replication. Rather, viral entry increased specifically in the hindbrain of IFNAR-deficient mice, suggesting that IFNAR signaling critically regulates BBB permeability in this brain region. Pattern recognition receptors and IFN-stimulated genes had higher basal and IFN-induced expression in human and mouse cerebellar astrocytes than did cerebral cortical astrocytes, suggesting that IFNAR signaling has brain region–specific roles in CNS immune responses. Taken together, our data identify cerebellar astrocytes as key responders to viral infection and highlight the existence of distinct innate immune programs in astrocytes from evolutionarily disparate regions of the CNS.

Authors

Brian P. Daniels, Harsha Jujjavarapu, Douglas M. Durrant, Jessica L. Williams, Richard R. Green, James P. White, Helen M. Lazear, Michael Gale Jr., Michael S. Diamond, Robyn S. Klein

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Figure 1

Survival and viral burden following s.c. WNV inoculation.

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Survival and viral burden following s.c. WNV inoculation. (A–I) Mice wer...
(A–I) Mice were inoculated s.c. with WNV (New York 2000 strain). (A) Mice were monitored daily for survival after infection. (B) Clinical scores of Ifnarfl/fl mice either positive or negative for Gfap-Cre (x axis) were recorded on the indicated post-infection days. 0 = subclinical; 1 = hunched/ruffled fur; 2 = altered gate/slow movement; 3 = no movement, but responsive to stimuli; 4 = moribund; 5 = dead. (C) Serum viral loads as measured by qRT-PCR. (D–G) Tissue viral loads as measured by plaque assay. (H) BBB permeability was measured by detection of sodium fluorescein accumulation in tissue homogenates derived from cerebral cortex or cerebellum. Data represent the mean ± SEM of individual mouse values normalized to serum sodium fluorescein concentration. Group means were then normalized to the mean values for uninfected controls. (I and J) Immunohistochemical detection of endogenous IgG accumulation in parenchymal CNS tissues. Signal intensities were quantified from two ×40 fields per region using ImageJ software. Scale bar: 100 μm. Data in A and B represent pooled data collected from 3 independent experiments for Ifnarfl/fl Cre– (n = 12), Ifnarfl/fl Gfap-Cre+ (n = 17), or Ifnar–/– (n = 8) mice. Data in C–G were collected from 2 to 3 independent experiments and represent values recorded for 4 to 10 mice per time point. Data in G–I were pooled from a total of 5 mice per time point and were collected from 2 independent experiments. *P < 0.05, **P < 0.01, and ***P < 0.001, by log-rank test (A), Mann-Whitney U test (C–G), or 2-way ANOVA (H and J).