Neuroimmunology; immunopathogenesis of viral infections of the central nervous system; innate immunity to viruses; immune mechanisms of neuronal and glial cell injury
1) Role of Pattern-Recognition Receptors and Innate Immunity in the CNS During Acute Viral Encephalitis
Microglia are the main endogenous myeloid cell population of the CNS. While these cells provide important beneficial immune functions during local immune responses within the brain, their aberrant or prolonged activation can result in neurodegeneration. Using a mouse model of acute alphavirus encephalitis, we have found that locally activated microglial cells facilitate neuronal injury through multiple mechanisms. How these cells become activated, however, is presently unknown. We hypothesize that signals arising from virus-infected neurons, either cellular or viral in origin, activate microglia via known pattern-recognition receptors (PRRs) to trigger pathogenic host responses. A combination of in vitro techniques and in vivo viral challenges of various PRR-deficient animals can be pursued to test this hypothesis.
2) Immune Mechanisms of Neuronal Injury in the CNS During Experimental Viral Encephalitis
Acute viral infection of the CNS causes substantial morbidity and mortality via direct viral damage of neurons, but we have recently determined that there is substantial bystander injury to uninfected neurons as well. Host responses arising from activated microglial cells are implicated in this bystander neuronal injury, although little is known about the immunological mechanisms underlying this cellular damage. We hypothesize that inflammatory mediators, including but not limited to nitric oxide, proinflammatory cytokines, and reactive oxygen species, are produced by activated microglia to directly or indirectly damage neurons. Successful progress towards addressing this hypothesis will likely require the use of various in vivo and ex vivo analysis methodologies to implicate individual inflammatory mediators in this aspect of disease pathogenesis.
Astrocytes are essential for CNS homeostasis and neuronal function. They are also well equipped to survive and function in the milieu of the inflamed CNS. During virus-induced neuroinflammation, astrocytes lose their capacity to take up the excitatory neurotransmitter, glutamate, causing neuronal cell death. In relapsing experimental autoimmune encephalomyelitis (EAE), an animal model of human multiple sclerosis (MS), astrocyte support of neuronal synapses becomes defective causing reversible neurological deficits. Both glutamate transporters and synaptogenic proteins produced by astrocytes appears to be directly influenced by the local inflammation. Ongoing studies aim to characterize the molecular mechanisms underlying these events with an eye towards developing novel therapies that prevent or reverse neuronal damage in these diseases.
Rainey-Barger EK, Rumble JM, Lalor SJ, Esen N, Segal BM, Irani DN. The lymphoid chemokine, CXCL13, is dispensable for the initial recruitment of B cells to the acutely inflamed central nervous system. Brain Behav Immun 2011;25:922-931.
Blakely P, Kleinschmidt-DeMasters BK, Tyler KL, Irani DN. Disrupted glutamate transporter expression in the spinal cord with acute flaccid paralysis due to West Nile Virus infection. J Neuropathol Exp Neurol 2009;68:1061-1072.
Prow NA, Irani DN. The inflammatory cytokine, interleukin-1 beta, mediates loss of astroglial glutamate transport and drives excitotoxic motor neuron injury in the spinal cord during acute viral encephalomyelitis. J Neurochem 2008;105:1276-1286.
Irani DN, Prow NA. Neuroprotective interventions targeting detrimental host immune responses protect mice from fatal alphavirus encephalitis. J Neuropathol Exp Neurol 2007;66:533-544.
Prow NA, Irani DN. The opioid receptor antagonist, naloxone, protects spinal motor neurons in a murine model of alphavirus encephalomyelitis. Exp Neurol 2007;205:461-470.
Darman J, Backovic S, Dike S, Maragakis NJ, Krishnan C, Rothstein JD, Irani DN* , Kerr DA*. Viral-induced spinal motor neuron death is non-cell-autonomous and involves glutamate neurotoxicity. J Neurosci 2004;24:7566-7575 (*co-corresponding authors).
Nargi-Aizenman JL, Havert MB, Zhang M, Irani DN, Rothstein JD, Griffin DE. Neural degeneration, paralysis and death due to acute viral encephalomyelitis are prevented by glutamate receptor antagonists. Ann Neurol 2004;55:541-549.
Kerr DA, Larsen T, Cook SH, Fannjiang Y-R, Choi E, Griffin DE , Hardwick JM, Irani DN. BCL-2 and BAX protect adult mice from lethal Sindbis virus infection but do not protect spinal motor neurons or prevent paralysis. J Virol 2002;76:10393-10400.
Havert MB , Schofield B, Griffin DE , Irani DN. Activation of divergent neuronal cell death pathways in different target cell populations during neuroadapted Sindbis virus infection of mice. J Virol 2000;74:5352-5356.