The protozoan parasite Toxoplasma gondii is an important infection causing life threatening disease in patients with HIV-AIDs and other immune suppressive conditions. Despite the activation of a robust immune response including high antibody titers in infected individuals, sterile cure is not achieved. Rather the parasite differentiates into a relatively metabolically quiescent tissue cyst form. Tissue cysts which establish within muscle and the CNS, are characterized by having a highly glycosylated cyst wall and matrix. A given cyst may contain several hundred individual parasites. Our studies using lectin reactivity have identified the presence of sialic acid containing glycans in the tissu cyst wall and matrix of both brain derived and tissue culture induced cysts. This finding is remarkable in light of the absence of any of the machinery for the synthesis, activation and transfer of sialic acid being found in the parasite genome. The implication of this finding is that host activities may be responsible for the sialylation of the tissue cyst associated glycans. In ths study we explore this radical hypothesis by using established host cell mutants with defects in distinct steps of the sialylation pathway to confirm the contribution of the host cell. In addition specific host activities will also be targeted using siRNA knockdowns to establish the classes of sialyltransferases involved. Finally we will develop as split GFP/Luc based system to address whether fusion of the parasitophorous vacuole membrane and the associated ER as well as the redirection of Golgi associated vesicles is involved in the delivery of cyst modifying glycosylatin enzymes from the host cell. We believe that by hijacking the host's own glycosylation machinery, the parasite may avoid detection by the immune system by effectively "sugar coating" potentially antigenic determinants with "self" sugars rendering them functionally invisible.

Public Health Relevance

Toxoplasma gondii causes serious illness in immune compromised individuals including patients with HIV- AIDS. Our understanding of the role of glycosylation in parasite biology is very limited. With this application we investigate a novel paradigm and address a potential mechanism by which host activities may glycosylated parasite proteins in the vacuolar space and the tissue cyst.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21AI099509-01A1
Application #
8451142
Study Section
Pathogenic Eukaryotes Study Section (PTHE)
Program Officer
Mcgugan, Glen C
Project Start
2013-01-18
Project End
2014-12-31
Budget Start
2013-01-18
Budget End
2013-12-31
Support Year
1
Fiscal Year
2013
Total Cost
$185,625
Indirect Cost
$60,625
Name
University of Kentucky
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
939017877
City
Lexington
State
KY
Country
United States
Zip Code
40506