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Infection and Immunity, February 2005, p. 1023-1033, Vol. 73, No. 2
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.2.1023-1033.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Sarcocystis neurona Merozoites Express a Family of Immunogenic Surface Antigens That Are Orthologues of the Toxoplasma gondii Surface Antigens (SAGs) and SAG-Related Sequences{dagger}

Daniel K. Howe,1* Rajshekhar Y. Gaji,1 Meaghan Mroz-Barrett,1 Marc-Jan Gubbels,2 Boris Striepen,2 and Shelby Stamper1

M. H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, Kentucky,1 Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, University of Georgia, Athens, Georgia2

Received 27 January 2004/ Returned for modification 28 February 2004/ Accepted 18 October 2004

Sarcocystis neurona is a member of the Apicomplexa that causes myelitis and encephalitis in horses but normally cycles between the opossum and small mammals. Analysis of an S. neurona expressed sequence tag (EST) database revealed four paralogous proteins that exhibit clear homology to the family of surface antigens (SAGs) and SAG-related sequences of Toxoplasma gondii. The primary peptide sequences of the S. neurona proteins are consistent with the two-domain structure that has been described for the T. gondii SAGs, and each was predicted to have an amino-terminal signal peptide and a carboxyl-terminal glycolipid anchor addition site, suggesting surface localization. All four proteins were confirmed to be membrane associated and displayed on the surface of S. neurona merozoites. Due to their surface localization and homology to T. gondii surface antigens, these S. neurona proteins were designated SnSAG1, SnSAG2, SnSAG3, and SnSAG4. Consistent with their homology, the SnSAGs elicited a robust immune response in infected and immunized animals, and their conserved structure further suggests that the SnSAGs similarly serve as adhesins for attachment to host cells. Whether the S. neurona SAG family is as extensive as the T. gondii SAG family remains unresolved, but it is probable that additional SnSAGs will be revealed as more S. neurona ESTs are generated. The existence of an SnSAG family in S. neurona indicates that expression of multiple related surface antigens is not unique to the ubiquitous organism T. gondii. Instead, the SAG gene family is a common trait that presumably has an essential, conserved function(s).

* Corresponding author. Mailing address: Department of Veterinary Science, 108 Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546-0099. Phone: (859) 257-4757, ext. 81113. Fax: (859) 257-8542. E-mail: dkhowe2{at}uky.edu.

{dagger} Kentucky Agricultural Experiment Station article no. 04-14-017.

Editor: J. F. Urban, Jr.

Infection and Immunity, February 2005, p. 1023-1033, Vol. 73, No. 2
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.2.1023-1033.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Hoane, J. S., Morrow, J. K., Saville, W. J., Dubey, J. P., Granstrom, D. E., Howe, D. K. (2005). Enzyme-Linked Immunosorbent Assays for Detection of Equine Antibodies Specific to Sarcocystis neurona Surface Antigens. CVI 12: 1050-1056 [Abstract] [Full Text]  
  • Vaishnava, S., Morrison, D. P., Gaji, R. Y., Murray, J. M., Entzeroth, R., Howe, D. K., Striepen, B. (2005). Plastid segregation and cell division in the apicomplexan parasite Sarcocystis neurona. J. Cell Sci. 118: 3397-3407 [Abstract] [Full Text]  


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