Date of Award

2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Cell & Molecular Biology

First Advisor

Boris Striepen

Abstract

Cryptosporidium is the second leading cause of severe diarrhea and diarrheal-related death in children worldwide. There are currently no vaccines and the only drug available has low efficacy in immunocompromised individuals who need it most. As an obligate intracellular parasite, Cryptosporidium relies heavily on its intestinal epithelial host cell to provide a niche for its growth and survival, but little is known about how the infected cell responds. We conducted a genome wide CRISPR/Cas9 knockout screen to discover host genes necessary for Cryptosporidium parvum infection. The most enriched genes indicate that interferon signaling, glycosaminoglycan (GAG) synthesis, and glycosylphosphatidylinositol (GPI) anchor biosynthesis are important for susceptibility to C. parvum infection and infection induced cell death. Our identification of the importance of genes required to produce sulfated GAGs supports previous research that a C-type lectin on the surface of the parasite binds to heparan sulfate to facilitate attachment. GPI anchor biosynthesis was also an important determinant of susceptibility to C. parvum infection. Further investigation revealed a type III interferon response to Cryptosporidium in human host cells, as well as in mice. Treatment of mice with IFNλ reduced infection burden and protected immunocompromised mice from severe outcomes, including death, with its effects requiring STAT1 signaling in the enterocyte. Initiation of the type III interferon response was abrogated in the absence of the pattern recognition receptor TLR3. Overall, we identify new host genes to investigate in the propagation of the parasite Cryptosporidium, as well as elucidate the upstream events required to initiate production of IFNλ in response to infection.

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