Publication Date

2018-07-31

Availability

Embargoed

Embargo Period

2020-07-31

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Microbiology and Immunology (Medicine)

Date of Defense

2018-07-23

First Committee Member

Thomas R. Malek

Second Committee Member

Zhibin Chen

Third Committee Member

Alberto Pugliese

Fourth Committee Member

Krishna V. Komanduri

Fifth Committee Member

Theodore J. Lampidis

Sixth Committee Member

Andrew D. Wells

Abstract

Deletion of interleukin-2 (IL-2) or IL-2 receptor (IL-2R) subunits in mice causes lethal autoimmunity, establishing the vital contribution of IL-2R signaling to thymic development of Foxp3+ Tregs. However, precise mechanisms of IL-2-driven functional programming in Tregs and pathogenic autoreactive T cells remain undefined. To investigate these issues, we characterized a germline knockout (gKO) versus Treg-targeted conditional knockout (cKO) of the IL-2Rα chain (CD25) in mice. Both KO models developed lethal autoimmunity, but disease onset was delayed in CD25 gKO mice due to IL-2 deprivation among CD4+ and CD8+ T cells. Foxp3+ thymocytes from gKO mice showed greater reduction in Treg suppressive markers than cKO mice, along with unique defects in Ki67 and Bcl-2 expression, suggesting that an early IL-2-dependent programming step operates prior to Foxp3 induction. To evaluate IL-2R signaling in mature Tregs independently of thymic development, we bred mouse strains allowing tamoxifen-inducible genetic ablation of CD25 and fate mapping within the Treg pool. IL-2R signaling was universally required for persistence of mature Tregs in the periphery, as CD25 KO Tregs were undetectable in all tissues examined by ~15 weeks post-induction. CD25 KO Tregs showed increased apoptosis, oxidative stress, and signs of mitochondrial dysfunction, along with reduced transcription of key enzymes of lipid and cholesterol biosynthetic pathways, suggesting that IL-2 governs mature Treg survival through a non-conventional mechanism of metabolic regulation. Divergent transcriptional changes in CD25 KO Tregs versus CD25 cKO Foxp3+ thymocytes indicate that IL-2R signaling in the thymus and the periphery represent two fundamentally distinct categories of influence.

Keywords

Tregs; IL-2; IL-2R; autoimmunity; tolerance; thymic development

Available for download on Friday, July 31, 2020

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