Abstract
BackgroundUsing a murine model of herpes simplex virus (HSV)-1 encephalitis, our laboratory has determined that induction of proinflammatory mediators in response to viral infection is largely mediated through a Toll-like receptor-2 (TLR2)-dependent mechanism. Published studies have shown that, like other inflammatory mediators, reactive oxygen species (ROS) are generated during viral brain infection. It is increasingly clear that ROS are responsible for facilitating secondary tissue damage during central nervous system infection and may contribute to neurotoxicity associated with herpes encephalitis.MethodsPurified microglial cell and mixed neural cell cultures were prepared from C57B/6 and TLR2-/- mice. Intracellular ROS production in cultured murine microglia was measured via 2', 7'-Dichlorofluorescin diacetate (DCFH-DA) oxidation. An assay for 8-isoprostane, a marker of lipid peroxidation, was utilized to measure free radical-associated cellular damage. Mixed neural cultures obtained from β-actin promoter-luciferase transgenic mice were used to detect neurotoxicity induced by HSV-infected microglia.ResultsStimulation with HSV-1 elevated intracellular ROS in wild-type microglial cell cultures, while TLR2-/- microglia displayed delayed and attenuated ROS production following viral infection. HSV-infected TLR2-/- microglia produced less neuronal oxidative damage to mixed neural cell cultures in comparison to HSV-infected wild-type microglia. Further, HSV-infected TLR2-/- microglia were found to be less cytotoxic to cultured neurons compared to HSV-infected wild-type microglia. These effects were associated with decreased activation of p38 MAPK and p42/p44 ERK in TLR2-/- mice.ConclusionsThese studies demonstrate the importance of microglial cell TLR2 in inducing oxidative stress and neuronal damage in response to viral infection.
Highlights
Using a murine model of herpes simplex virus (HSV)-1 encephalitis, our laboratory has determined that induction of proinflammatory mediators in response to viral infection is largely mediated through a Toll-like receptor-2 (TLR2)-dependent mechanism
Compared to wild-type microglia, TLR2-/microglia displayed attenuated HSV-induced lipid peroxidation and neurotoxicity. These studies demonstrate the importance of microglial cell TLR2 in inducing oxidative stress and neuronal damage in response to viral infection
TLR2-/- microglial cells have blunted reactive oxygen species (ROS) production in response to HSV-1 infection To determine the role of microglia and TLR2 on HSV-1 induced oxidative damage, we first examined ROS production in wild-type microglia following HSV-1 infection in vitro
Summary
Using a murine model of herpes simplex virus (HSV)-1 encephalitis, our laboratory has determined that induction of proinflammatory mediators in response to viral infection is largely mediated through a Toll-like receptor-2 (TLR2)-dependent mechanism. Published studies have shown that, like other inflammatory mediators, reactive oxygen species (ROS) are generated during viral brain infection. It is increasingly clear that ROS are responsible for facilitating secondary tissue damage during central nervous system infection and may contribute to neurotoxicity associated with herpes encephalitis. Exposure to an invading pathogen initially triggers robust innate immune responses These responses involve recruitment and activation of phagocytic macrophages, neutrophils and, during central nervous system infection, the activation of resident microglia. It is becoming increasingly clear that reactive species are responsible for mediating many of the secondary mechanisms of tissue damage during and subsequent to viral brain infection, including herpes encephalitis [6]
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