Molecular Mechanisms of the Activation of the Pattern Recognition Receptor Dectin-1 and its Induction of Immune Responses

• Author / Creator

  Fitieh, Amira

• In the past two decades, a rising number of fungi have emerged as serious human pathogens and the incidence of invasive fungal infections has increased enormously. Millions of people contract fungal diseases that kill at least as many people as tuberculosis or malaria, yet the global burden of fungal disease is largely unrecognized. This rise in fungal disease burden has become a public health concern and major threat to human health, especially in immunocompromised patients, whose numbers are increasing due to the advent of HIV, organ transplantations, and the use of immuno-suppressive therapies for auto-immune diseases and cancer. Despite the high mortality rates of invasive fungal infections, they remain understudied compared to other infections, and to date the molecular mechanisms of antifungal immune responses are still poorly understood. It is therefore a healthcare priority and an exciting challenge to understand at the molecular level the mechanisms that our immune system utilizes to fight fungal infections. With this goal in mind, I have been particularly interested in studying the first and crucial step of this process: the recognition of specific molecules of the fungal pathogen by receptors expressed on the surface of innate immune cells. Work presented in this thesis focuses on Dectin-1, an innate immune receptor that plays a key role in antifungal immunity. Dectin-1 is the major receptor for β-glucans, which are polysaccharides that are largely present in the fungal cell wall. The exact molecular mechanisms of how Dectin-1 is activated by β-glucans and how it induces intracellular signaling are still not clear and need to be elucidated. Previous studies have shown that depending on the size of the ligand, Dectin-1 can activate, inhibit or modify receptor signaling. Based on these studies, we hypothesized that binding of β-glucans to Dectin-1 would cause it to cluster into multimeric complexes, which would act as signaling nodes to initiate intracellular signaling and subsequent immune responses. To perform this analysis, we employed conventional biochemical approaches and cell biological approaches, combined with quantitative superresolution microscopy. We were able to characterize the relationship between receptor clustering and Dectin-1 signal-transduction. Herein, results from this thesis provide a “Receptor Clustering Model” for Dectin-1 activation and induction of antifungal immune responses. With this better understanding of the mechanisms of antifungal immunity activation by Dectin-1, we sought to design, in collaboration with the group of Dr. Bundle (Dept. of Chemistry, U of A), a new anti-Candida vaccine. We were able to show that a multimeric β-glucan conjugate, developed by this group, is capable of producing enhanced antifungal immunostimulatory effects. Overall, findings from my PhD thesis provide valuable mechanistic insights into the early signaling and molecular events that lead to Dectin-1 activation and its subsequent capacity to induce antifungal immune responses. Finally, work presented here sets a framework for sophisticated development of novel and more effective antifungal therapeutics, and provides considerations for better design of antifungal vaccines, a significant area to be pursued in the near future. Therefore, findings from this thesis will ultimately establish a foundation for hopefully effective treatment and prevention of fungal infections.

• Subjects / Keywords

  • C-type lectin Receptors (CLRs)
  • Dectin-1
  • Β-glucans

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3WP9TN34

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.