Zika (PRVABC59) Infection Is Associated with T cell Infiltration and Neurodegeneration in CNS of Immunocompetent Neonatal C57Bl/6 Mice

Published: November 17, 2016
http://dx.doi.org/10.1371/journal.ppat.1006004

Abstract

The recent spread of Zika virus (ZIKV) and its association with increased rates of Guillain Barre and other neurological disorders as well as congenital defects that include microcephaly has created an urgent need to develop animal models to examine the pathogenesis of the disease and explore the efficacy of potential therapeutics and vaccines. Recently developed infection models for ZIKV utilize mice defective in interferon responses. In this study we establish and characterize a new model of peripheral ZIKV infection using immunocompetent neonatal C57BL/6 mice and compare its clinical progression, virus distribution, immune response, and neuropathology with that of C57BL/6-IFNAR KO mice. We show that while ZIKV infected IFNAR KO mice develop bilateral hind limb paralysis and die 5–6 days post-infection (dpi), immunocompetent B6 WT mice develop signs of neurological disease including unsteady gait, kinetic tremors, severe ataxia and seizures by 13 dpi that subside gradually over 2 weeks. Immunohistochemistry show viral antigen predominantly in cerebellum at the peak of the disease in both models. However, whereas IFNAR KO mice showed infiltration by neutrophils and macrophages and higher expression of IL-1, IL-6 and Cox2, B6 WT mice show a cellular infiltration in the CNS composed predominantly of T cells, particularly CD8+ T cells, and increased mRNA expression levels of IFNg, GzmB and Prf1 at peak of disease. Lastly, the CNS of B6 WT mice shows evidence of neurodegeneration predominantly in the cerebellum that are less prominent in mice lacking the IFN response possibly due to the difference in cellular infiltrates and rapid progression of the disease in that model. The development of the B6 WT model of ZIKV infection will provide insight into the immunopathology of the virus and facilitate assessments of possible therapeutics and vaccines.

Author Summary

The recent spread of Zika virus (ZIKV) and its association with increased rates of neurological disorders and congenital defects created an urgent need for animal models to examine the pathogenesis of the disease and explore the efficacy of potential therapeutics and vaccines. We describe the first symptomatic PRVABC59(ZIKV) animal model in immunocompetent B6 WT mice showing that a subcutaneous challenge in 1 day old mice leads to non-lethal neurological disease that is characterized by unsteady gait, kinetic tremors, severe ataxia and seizures that subsides after 2 weeks. ZIKV infects neurons in cerebellum of mice and elicits the infiltration of lymphocytes into the brain. The immune response protects mice from death but may also contribute to neurodegeneration as mice with defective interferon responses have increased virus loads in brain and peripheral organs, succumbing to the disease in 5–6 days, but have fewer signs of neurodegeneration. This mouse model bypasses transplacental transmission and consequent placental insufficiency and will facilitate detailed investigations into the pathogenesis of the disease as well as mechanistic studies for possible therapeutics and vaccines. Lastly, its non-lethal outcome allows for studies assessing the long term effects of the infection, and exploring conditions that could lead to disease reactivation.