The Distribution of Neospora caninum Secretory Proteins in Mouse and Calf Brains

<i>Neospora caninum</i>, as well as <i>Toxoplasma gondii</i>, secrete proteins that facilitate the invasion of host cells and the regulation of host immune response and metabolism. However, the localization of the secretory proteins in infected animal brains has not been studied in detail. Here, we investigate the brain and intracellular distribution of the secretory proteins in experimentally infected mice and naturally infected calves through histopathology and immunohistochemistry (IHC) to detect surface antigen 1 (NcSAG1), cyclophilin (NcCYP), profilin (NcPF), dense granule protein 6 (NcGRA6), and NcGRA7. These methods revealed that numerous tachyzoites positive for NcSAG1, NcCYP, NcPF, NcGRA6, and NcGRA7 were localized in and around the animals' necrotic lesions, and NcGRA7 was diffusely observed in the necrotic lesions of the infected mice. Moreover, IHC revealed that NcGRA6 and NcGRA7 were distributed in the cytoplasm of infected neurons around the parasites in the infected mice and calves. This suggests that NcGRA6 and NcGRA7 might be directly related to the alteration of neuronal metabolism and activity, and that NcGRA7 might be related to the formation of necrotic lesions.