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Investigation of the SnSAG gene family of surface antigens in the coccidian parasite Sarcocystis neurona
Department of Veterinary Sciences
Equine protozoal myeloencephalitis (EPM) is a common and debilitating neurolgic disease of horses that is caused by the protozoan pathogen Sarcocystis neurona. Efforts to correctly diagnose, treat, and prevent EPM have been partly hampered by a lack of information about the pathogen. This project will investigate a group of parasite surface proteins that are very immunogenic and likely important for the pathogen's survival. The information gained from these studies could lead to better EPM diagnostics and a protective vaccine.
2009 Project Description
The Sarcocystis neurona SnSAGs have been expressed in bacteria as full-length proteins, as partial proteins (single domain of the prototypic SnSAG two-domain structure), and as chimeric fusions (e.g., SnSAG2-SnSAG3 fusions). Combinations of the recombinant SnSAGs have been tested in enzyme-linked immunosorbent assays (ELISAs) to assess whether improved diagnostic accuracy can be achieved over our previous ELISAs that incorporated the single recombinant SnSAG proteins. Based on a small sample set of sera characterized by the gold standard western blot, slight improvement in serologic accuracy was achieved using either a cocktail of SnSAG3 and SnSAG4 or the single SnSAG4/3 fusion protein.
Collaboration with a commercial equine testing company is working to validate the modified ELISAs for diagnosis of equine protozoal myeloencephalitis. Experiments have been initiated to determine whether the SnSAGs are expressed during all life cycle stages (merozoites, bradyzoites, sporozoites). Western blot analyses of S. neurona strain SN138 sporozoites suggest that SnSAG2, SnSAG3, and SnSAG4 are present during this life cycle stage but the SnSAG5 major surface antigen of this strain is not expressed.
Immunohistochemical staining of sarcocysts in tissue sections will be conducted to determine if the SnSAGs are expressed during the bradyzoite life cycle stage. A study investigating control of SnSAG gene expression revealed an important cis-acting element in the promoter region of the SnSAG1 gene.
The SnSAG surface antigens are abundant and highly immunogenic parasite proteins expressed by the equine pathogen, Sarcocystis neurona. In-depth characterization of the SnSAGs and the identification of new parasite surface proteins will provide insight into the importance of these molecules during S. neurona infection and intracellular propagation. In turn, this information should prove useful for our efforts to develop methods for improved diagnostics and protective vaccination against the debilitating neurologic disease, EPM.
Gaji, R.Y., and D.K. Howe. (2009) The heptanucleotide motif GAGACGC is a key component of a cis-acting element that is critical for SnSAG1 expression in Sarcocystis neurona. Molecular and Biochemical Parasitology 166:85-88.