A number of viruses can infect the brain by traveling up the axons of olfactory receptor neurons into the olfactory bulb. Rarely, however, do any of these viruses spread to the rest of the brain-a phenomenon of neuroprotection whose mechanisms are not well understood. In mice infected with RNA-based vesicular stomatitis virus (VSV) or DNA-based cytomegalovirus, researchers from Yale University found evidence of antiviral interferon-stimulated gene (IFG) expression as far away as the posterior brain, even though they could not detect any nearby virus. This distant interferon response was important for stopping the spread of infection. When the team knocked out the receptor for interferon-α/β in mice infected with VSV, the virus spread throughout the brain and the mice died.
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