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Infection and Immunity, January 2008, p. 103-110, Vol. 76, No. 1
0019-9567/08/$08.00+0     doi:10.1128/IAI.01170-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Highly Polymorphic Family of Glycosylphosphatidylinositol-Anchored Surface Antigens with Evidence of Developmental Regulation in Toxoplasma gondii{triangledown}

Angela M. Pollard,1 Krystal N. Onatolu,1 Luisa Hiller,2,{dagger} Kasturi Haldar,2 and Laura J. Knoll1*

Department of Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison, Wisconsin 53706,1 Department of Pathology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 606112

Received 23 August 2007/ Returned for modification 29 September 2007/ Accepted 7 October 2007

The life cycle of the apicomplexan parasite Toxoplasma gondii requires that an infectious cyst develop and be maintained throughout the life of the host. The molecules displayed on the parasite surface are important in controlling the immune response to the parasite. T. gondii has a superfamily of glycosylphosphatidylinositol (GPI)-anchored surface antigens, termed the surface antigen (SAG) and SAG-related surface antigens, that are developmentally regulated during infection. Using a clustering algorithm, we identified a new family of 31 surface proteins that are predicted to be GPI anchored but are unrelated to the SAG proteins, and thus we named these proteins SAG-unrelated surface antigens (SUSA). Analysis of the single nucleotide polymorphism density showed that the members of this family are the most polymorphic genes within the T. gondii genome. Immunofluorescence of SUSA1 and SUSA2, two members of the family, revealed that they are found on the parasite surface. We confirmed that SUSA1 and SUSA2 are GPI anchored by phospholipase cleavage. Analysis of expressed sequence tags (ESTs) revealed that SUSA1 had 22 of 23 ESTs from chronic infection. Analysis of mRNA and protein confirmed that SUSA1 is highly expressed in the chronic form of the parasite. Sera from mice with chronic T. gondii infection reacted to SUSA1, indicating that SUSA1 interacts with the host immune system during infection. This group of proteins likely represents a new family of polymorphic GPI-anchored surface antigens that are recognized by the host's immune system and whose expression is regulated during infection.

* Corresponding author. Mailing address: Department of Medical Microbiology and Immunology, University of Wisconsin—Madison, 1300 University Avenue, Madison, WI 53706. Phone: (608) 262-3161. Fax: (608) 262-8418. E-mail: ljknoll{at}wisc.edu

{triangledown} Published ahead of print on 15 October 2007.

Editor: W. A. Petri, Jr.

{dagger} Present address: Center for Genomic Sciences, Allegheny-Singer Research Institute, Allegheny General Hospital, 320 E. North Ave., Pittsburgh, PA 15212.

Infection and Immunity, January 2008, p. 103-110, Vol. 76, No. 1
0019-9567/08/$08.00+0     doi:10.1128/IAI.01170-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Pollard, A. M., Skariah, S., Mordue, D. G., Knoll, L. J. (2009). A Transmembrane Domain-Containing Surface Protein from Toxoplasma gondii Augments Replication in Activated Immune Cells and Establishment of a Chronic Infection. Infect. Immun. 77: 3731-3739 [Abstract] [Full Text]  


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