Defining neuronal responses to the neurotropic parasite Toxoplasma gondii

A select group of pathogens infects neurons in the brain. Prior dogma held that neurons were “defenseless” against infecting microbes, but many studies suggest that neurons can mount anti-microbial defenses. However, a knowledge gap in understanding how neurons respond in vitro and in vivo to different classes of microorganisms remains. To address this gap, we compared a transcriptional data set derived from primary neuron cultures (PNCs) infected with the neurotropic intracellular parasite Toxoplasma gondii with a data set derived from neurons injected with T. gondii protein in vivo. These curated responses were then compared to the transcriptional responses of PNCs infected with the single-stranded RNA viruses, West Nile virus or Zika virus. These analyses highlighted a conserved response to infection associated with chemokines (Cxcl10, Ccl2) and cytokines (interferon signaling). However, T. gondii had diminished IFN-α signaling in vitro compared to the viral data sets and was uniquely associated with a decrease in neuron-specific genes (Snap25, Slc17a7, Prkcg). These data underscore that neurons participate in infection-induced neuroinflammation and illustrate that neurons possess both pathogen-specific and pathogen-conserved responses.