Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Earl H. Weidner


Toxoplasma gondii is an obligate intracellular protozoan parasite of the Phylum Apicomplexa. The parasite resides in the cytoplasm of its host cells in a membrane bound compartment called the parasitophorous vacuole. All growth and development of the parasite occur within this compartment. In this thesis, the interactions between the Vero cells, a fibroblast-like cell line, and the parasite which occur during the intracellular growth of the parasite were addressed. The impact of infection on the host cell intermediate filaments and microtubular cytoskeletal elements was examined by immunofluorescence microscopy. Host cell intermediate filaments were found to overcoat the parasite vacuole beginning shortly after invasion and persisting throughout the course of infection. Evidence indicates the host cell vimentin binds to the parasitophorous vacuole serving to dock the vacuole to the host cell nuclear surface. Host cell microtubules were also found to overcoat the parasitophorous vacuole and were increasing accumulated around the parasite compartment throughout the infection. Unlike the intermediate filaments however, the microtubules were not involved in juxtanuclear positioning of the vacuoles. Neither were the microtubules found to be involved in the mitochondrial or vimentin overcoating of the vacuoles. However, the infection had a dramatic impact on the organization of the host cell endoplasmic reticulum. This data suggests the microtubular associations with membranous organelles might be disrupted in infected cells. A membranous network occurs within the parasitophorous vacuole which is thought to transport membrane and proteins from the parasite to the parasitophorous vacuolar membrane. The presence of GTP-binding proteins on the networks was investigated. A 25 kDa GTP-binding protein was found to be present on the networks. Additionally, the parasite was found to contain a 41 kDa GTP-binding protein. The 41 kDa protein was not found on the networks but rather localized to the inner membrane complex, a parasite organelle involved in secretion of the networks. These results indicate GTP-binding proteins are important in the secretion of the membranous networks into the parasitophorous vacuole and may function in directing membrane traffic within the parasitophorous vacuole.