Hsp70 and a Novel Axis of Type 1 Interferon-Dependent Antiviral Immunity in the Measles Virus-Infected Brain

The major inducible 70 kDa heat shock protein (hsp70) is host protective in a mouse model of measles virus (MeV) brain infection. Transgenic constitutive expression of hsp70 in neurons, the primary target of MeV infection, abrogates neurovirulence in neonatal H-2d congenic C57BL/6 mice. A significant level of protection is retained after depletion of T lymphocytes, implicating innate immune mechanisms. Focus of the present work was to elucidate the basis for hsp70-dependent innate immunity using this model. Transcriptome analysis of brains from transgenic (TG) and non-transgenic (NT) mice 5 days after infection identified type 1 interferon (IFN) signaling and macrophage activation/antigen presentation as the main differences linked to survival. The pivotal role for type 1 IFN in hsp70-mediated protection was demonstrated in mice with a genetically disrupted type 1 IFN receptor (IFNAR-/-), where IFNAR-/- eliminated the difference in survival between TG and NT mice. Brain macrophages, not neurons, are the predominant source of type 1 IFN in the virus-infected brain, and in vitro studies provided a mechanistic basis by which MeV-infected neurons can induce IFN- in uninfected microglia in an hsp70-dependent manner. MeV infection induced extracellular release of hsp70 from mouse neuronal cells that constitutively express hsp70, and extracellular hsp70 induced IFN- transcription in mouse microglial cells through Toll-like receptors 2 and 4. Collectively, results support a novel axis of type 1 IFN-dependent antiviral immunity in the virus-infected brain that is driven by hsp70.

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Kim MY, Shu Y, Carsillo T, Zhang J, Yu L, Peterson C, Longhi S, Girod S, Niewiesk S, Oglesbee M