Neuro -immune mechanisms in response to Venezuelan equine encephalitis virus infection.

摘要

Venezuelan equine encephalitis virus (VEE) is an emerging pathogen with epizootics and epidemics occurring in the Western Hemisphere. Recent outbreaks in South America have caused significant morbidity and mortality among domesticated livestock and surrounding human communities. VEE pathogenesis is characterized by infection of the central nervous system (CNS) where the virus targets neurons, resulting in significant neurodegeneration. VEE encephalitis can result in profound neurological deficits or even death. Because of the devastating nature of this disease and the lack of interventional therapies, it is important to understand the intricate details of VEE neuropathogenesis in order to identify targets for treatment to effect a cure.;Inflammation has recently been implicated as a component of neurodegeneration. Inflammation in the CNS in response to acute infections is a protective mechanism that attempts to contain and clear neuro-invasive pathogens, however this upregulation of pro-inflammatory genes may be deleterious to surrounding neurons. The combined effects of direct infection and inflammation may be additive or synergistic in the amount of injury sustained in the CNS.;Glial cells are of particular importance in the CNS immune response. These resident cells of the CNS have intimate associations with neurons and regulate the CNS milieu. One type of glial cell is the astrocyte. Astrocytes are found in vast numbers in the CNS and have essential functional roles in maintaining a healthy environment for neurons. Further, astrocytes play a role in the pro-inflammatory innate immune response.;To identify the role of astrocytes in VEE infection, I characterized astrocyte susceptibility to VEE infection using an in vitro culture system and have further described their pro-inflammatory responses following VEE infection. Specifically, inducible nitric oxide synthase, tumor necrosis factor-alpha, and interleukin-6 are upregulated in response to VEE infection in primary astrocyte cultures as shown by reverse transcriptase-polymerase chain reaction and analyses of protein synthesis. I have also demonstrated that there were quantitative differences in the upregulation of these responses between virulent and attenuated strains of VEE.;To characterize the pro-inflammatory response in vivo, I measured cytokine gene expression in the CNS using a murine model of VEE infection. The cytokine responses to virulent VEE resulted in the upregulation of multiple genes important in inflammation and apoptosis. In contrast, cytokine responses in the CNS were delayed or absent following infection with attenuated VEE, depending on the specific mutant VEE strain.;Finally, CNS tissue from mice infected with VEE was double-labeled for astrocytosis and apoptosis, and stained for VEE antigen in adjacent tissue sections. Apoptosis occurs not only in areas of the brain where VEE antigen could be detected, but also in areas of acute astrogliosis, where no VEE antigen could be demonstrated. This association of apoptosis and astrogliosis suggests that inflammation may be contributing to neuronal degeneration in response to VEE infection.