Innate Immunity Of The Intestinal Epithelium During Toxoplasma Gondii Infection
The single layer of epithelial cells that line the intestinal tract provides both a physiologic and immunologic barrier for microbes and foreign antigens. Intestinal epithelial cells are differentiated into different functional subtypes and have regulatory roles in maintaining the homeostasis of the gut as well as initiating inflammatory responses during pathogenic infections. Toxoplasma gondii is a widespread zoonotic protozoan parasite that infects warm-blooded animals. Infection usually occurs through ingestion of T. gondii contaminated food or water. Therefore, natural route of infection has revealed the importance of epithelial cell response in influencing the outcome of the local and systemic immune response. In this thesis, I examined the innate immune response of intestinal epithelial cell during T. gondii infection. The immediate response upon intestinal epithelial and parasite contact revealed that T. gondii infected epithelial cells elicited MAPK phosphorylation, NF-!B activation, and secretion of IL-8 as well as several other inflammatory cytokines and chemokines in epithelial cells. I found that activation of MAPK and production of IL-8 was dependent on the MyD88 signaling pathway, and TLR2 was sufficient for parasite induced signaling in HEK 293 transfected cells. In addition, TLR2 signaling plays an important role in modulating of the local intestinal environment by inducing migration of dendritic cells into the follicle-associated epithelium of Peyer's patches. Using the susceptible C57BL/6 mice as a model, morphological changes of different intestinal epithelial cell subtypes in response to peroral T. gondii infection were further characterized. Oral infection with T. gondii ME49 cysts induced intestinal pathology and morphological changes of different epithelial cell subtypes. Mice deficient in TLR2 were more resistant to intestinal pathology and associated morphological changes. Parasite-derived TLR2 stimulatory molecules were found to be present in the supernatant collected from T. gondii infected cells. Therefore, potential biological significance of the activity in supernatants from T. gondii infected cells was also investigated. I found that the supernatants from T. gondii infected cells enhanced luminal antigen uptake and induced TLR2-dependent migration of dendritic cells to the follicle associated epithelium of Peyer's patches. Furthermore, analysis of the supernatant revealed several T. gondii proteins, and the GPI-anchored surface antigen-1 contributes to TLR2 stimulatory activity. In summary, this dissertation explores the innate immune response of the intestinal epithelium during T. gondii infection. The signaling pathways of intestinal epithelial cells elicited by the parasite as well as the modulation of the local intestinal environment can help us better understand the immunopathogenesis of T. gondii infection.
Innate immunity; Intestinal epithelial cells; Toxoplasma gondii
Leifer, Cynthia Anne
Denkers, Eric Young; Marquis, Helene; Clark, Theodore G.
Ph.D. of Veterinary Medicine
Doctor of Philosophy
dissertation or thesis