Alphaviruses are important causes of fatal encephalitis in humans worldwide. Many are also designated as Category B Priority Pathogens by the U.S. Public Health Service given their potential use as bioterrorism agents. One alphavirus, Sindbis virus (SV), has been extensively studied in a murine model. In particular, a neuroadapted strain (NSV) induces a highly reproducible disease in susceptible hosts with hindlimb paralysis and death that evolves over a period of 7-10 days. All strains of SV target neurons in the brain and spinal cord, and the fate of these cells determines neurovirulence. Further, non-infected neurons are also damaged via bystander mechanisms, and host immune responses have now been implicated in this aspect of viral pathogenesis. We know that microglia, the endogenous macrophage-like cell of the central nervous system (CNS), become activated soon after NSV infection, and we now show that two unrelated drugs that inhibit this microglial activation process also protect mice from NSV-induced hindlimb paralysis and death without exerting any effect on CNS viral replication or spread. In order to study this unique form of protection against NSV encephalomyelitis in greater detail, we propose: (1) To further characterize the beneficial effects of neuroprotective drugs in NSV-infected mice using treatment regimens where dosing begins only at or after the onset of overt neurologic disease, to characterize the effects of other anti-inflammatory agents known to target microglia in our model, and to verify the effects of all our protective agents against other New World alphaviruses that cause fatal encephalitis in humans, (2) To investigate histopathological correlates of drug-mediated protection from NSV-induced hindlimb paralysis and death, and to further characterize how each drug affects microglial activation in the CNS in vivo and microglial-induced injury of primary neurons iin vitro, (3) To compare temporal patterns of gene expression in purified tissue microglia from NSV-infected animals with or without protective drug treatment using cDNA microarray methodologies, and (4) To functionally characterize candidate genes identified by cDNA microarray analysis that are modulated by protective drug treatment regimens and to determine whether these candidates contribute to NSV pathogenesis in vivo and to microglial-induced neurotoxicity in vitro.
