CD1d-reactive invariant Natural Killer T cells (iNKT) are a T cell subset that have characteristics of both innate immune cells and adaptive immune cells. As a result, they are considered a bridge between the innate and the adaptive immune response. iNKT cells can rapidly secrete a variety of cytokines after activation, and therefore have an important immunomodulatory role during the immune response in many different diseases, such as cancer, asthma, autoimmune disease, and infection. During infections, there are three models of iNKT cell activation: activation requiring microbial antigen, cytokine driven activation, and activation requiring self-antigen. However, how iNKT cells become activated during some infections remains controversial, as activation requiring self-antigen has only been indirectly shown. Therefore, I addressed this controversy using an antigen receptor signal strength reporter mouse, in which Nur77gfp reports stimulation of the T cell receptor (TCR). Although the sensitivity of this reporter mouse was initially observed in conventional T cells, I showed that Nur77gfp is also a sensitive readout for TCR stimulation in iNKT cells. Therefore, several bacterial and viral infections were examined for the role of antigen-dependent versus antigen-independent activation. These experiments showed that Nur77gfp was upregulated during infections with a microbial antigen, and was not upregulated during an infection previously considered to activate iNKT cells by the cytokine driven model. Unexpectedly, the infectious contexts reported to require self-antigen for iNKT cell activation did not upregulate Nur77gfp, indicating that the main driver of iNKT cell activation is cytokine, and thus activation is antigen-independent. Additionally, as a result of the immunomodulatory capabilities of iNKT cells, iNKT cells have great potential for use in new therapeutics. However, for these therapies to be effective, an exogenous source of iNKT cells is needed. Therefore, I adapted the OP9-DL1 culture system to derive iNKT cells from hematopoietic progenitor cells in vitro. I showed that the frequency of cells expressing the iNKT TCR needed to be increased in order to detect iNKT cells using this system. Furthermore, I showed that the addition of IL-15 can enhance the percentage of cells expressing the NKT1 subset transcription factor Tbet. Therefore, this iNKT cell adapted OP9-DL1 culture system can be used as a new method to examine factors that influence iNKT cell development and to identify factors that can skew iNKT cell subset differentiation. Ultimately, these experiments aided in advancing the understanding of iNKT cell activation and development, as well as how to harness the power of iNKT cells to artificially orchestrate an immune response for therapeutic use.
University of Minnesota Ph.D. dissertation. May 2014. Major: Molecular, Cellular, Developmental Biology and Genetics. Advisor: Kristin A. Hogquist. 1 computer file (PDF); viii, 118 pages.
Holzapfel, Keli Lee.
The role of antigen receptor signaling in activation and development of invariant Natural Killer T cells.
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