Date of Award

Winter 12-15-2021

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Immunology)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Over the past decade, the cGAS-STING pathway has emerged as a principal component of innate DNA sensing. Its activation of type I interferon (IFN) elicits host immune activation and in the absence of cGAS or STING, mice are rendered critically susceptible to infection by viruses and bacteria. Breakdowns in the molecules that regulate this pathway can promote unrestrained cGAS-STING activation and the development of various forms of autoimmune disease. For instance, gain-of-function mutations in STING cause autoinflammatory lung disease in mice and STING-associated vasculopathy with onset in infancy (SAVI) in humans. However, our understanding of the mechanisms that underlie STING-dependent autoimmunity is poorly understood. SAVI-associated STING mutants have been demonstrated to incur ligand- independent signaling and the resulting constitutive activation of type I IFN is thought to underlie SAVI disease progression. However, a requirement for cGAS or type I IFN in SAVI has not been experimentally tested in animal models of this disease. Moreover, T-cell cytopenia is a hallmark of SAVI, but a role T or B cells in SAVI disease progression is unclear. During my dissertation, a growing number of type I IFN-independent signaling modalities were reported downstream of STING. These included production of type II and type III IFN. However, a role for either of these molecules in STING-dependent autoimmunity had not previously been addressed. Here, we examine the molecular mechanisms of gain-of-function STING signaling (Chapter 2); we define the requirements for cGAS, IRF3, IRF7 and adaptive immunity in murine SAVI disease (Chapter 3); and we determine the contributions of the type I (IFNAR1), type II (IFNGR1) and type III IFN (IFNLR1) receptors in the regulation of autoinflammatory lung disease and T-cell cytopenia in SAVI mice (Chapter 4).We found that spontaneous signaling of a SAVI-associated mutant, STING N154S, requires His157 and that non-covalent bonds, but not disulfide bonds, mediate native STING dimerization. We found that the absence of Rag1 entirely prevents SAVI lung disease, and only minimally develops when Tcrb is absent. Our analysis of T-cell subsets within SAVI mice revealed they are mostly highly differentiated effector cells and exhibit a dramatic loss of naïve and regulatory T cell populations. We determined that concomitant deletion Ifngr1 but not cGas, Irf3, Irf7, Ifnar1, or Ifnlr1 markedly improves lung disease. Moreover, we found that this coincided with a pronounced improvement in naïve and regulatory T cells. In cell culture and mixed bone marrow chimera studies, we found that the type II IFN receptor regulates the proliferation and survival of SAVI T cells. Overall, these results suggest that SAVI is a type II, but not type I interferonopathy. Lastly, SAVI mice fail to develop lymph nodes (LNs) and Peyer’s patches (PPs). The final goal of our study was to determine the contributions of the IFN receptors to STING- mediated abrogation of lymphorganogenesis (Chapter 5). We found that LNs, but not, PPs are restored in the absence of IFNGR1, but not IFNAR1 or IFNR1. Additionally, we found that the absence of the type II IFN receptor did not correct LN-deficiency in a STING N153S animal. Taken together, these findings indicate that STING and IFNGR1 exhibit broad cooperation, regulating not only autoimmune disease progression, but also lymphorganogenesis. Given the intense scrutiny of the STING pathway in the treatment of various autoimmune disease, cancer, and infections, our findings warrant further study of the intersection between STING and IFNGR1.

Language

English (en)

Chair and Committee

Jonathan Miner

Committee Members

Megan Baldridge

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