Innate immune defenses help restrict growth of the protozoan pathogen Toxoplasma gondii, but their efficacy is offset by parasite counter defenses. For example, infected macrophages attempt to destroy the parasite by expressing immunity-related GTPases (IRGs) that load onto and dismantle the parasitophorous membrane, but the parasite thwarts this by phosphorylating Irg proteins to diminish their activity. Since phosphorylation is a reversible, and therefore temporary, we hypothesize that T. gondii additionally eliminates these host effector proteins permanently by internalizing them into its endocytic system. Our recent unexpected finding that the parasite readily internalizes a reporter protein expressed in the host cytosol supports this hypothesis. Further, the reporter protein is most abundantly seen in protease-deficient parasites, suggesting that internalized host proteins are normally digested in the parasite endocytic system. Also, parasites deficient in the biogenesis of tubular membranes within the parasitophorous vacuole are unable to efficiently internalize the reporter protein, indicating that the tubular membranes are required for uptake. These deficient parasites are also highly susceptible to killing by activated macrophages.
The specific aims are to: (1) confirm the parasite endocytic system as the destination of internalized proteins;and (2) show that Toxoplasma uses the intravacuolar network of tubular membranes to internalize IRGs for destruction in its endolysosomal system. We expect to show that the parasite eliminates IRGs by endocytosis and degradation as an immune evasion strategy. The work is anticipated to open exciting new opportunities to diminish parasite intracellular survival during infection.

Public Health Relevance

We will further define a novel counter defense system that the brain parasite Toxoplasma gondii uses to thwart host innate immunity, ensuring its survival during infection. This research is expected to open new opportunities to attenuated parasite intracellular survival.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21AI097099-02
Application #
8604674
Study Section
Pathogenic Eukaryotes Study Section (PTHE)
Program Officer
Wali, Tonu M
Project Start
2013-01-15
Project End
2014-12-31
Budget Start
2014-01-01
Budget End
2014-12-31
Support Year
2
Fiscal Year
2014
Total Cost
$209,925
Indirect Cost
$74,925
Name
University of Michigan Ann Arbor
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Dou, Zhicheng; McGovern, Olivia L; Di Cristina, Manlio et al. (2014) Toxoplasma gondii ingests and digests host cytosolic proteins. MBio 5:e01188-14
Tomavo, Stanislas; Slomianny, Christian; Meissner, Markus et al. (2013) Protein trafficking through the endosomal system prepares intracellular parasites for a home invasion. PLoS Pathog 9:e1003629
Blackman, Michael J; Carruthers, Vern B (2013) Recent insights into apicomplexan parasite egress provide new views to a kill. Curr Opin Microbiol 16:459-64