Abstract
Giant cell arteritis (GCA), the most common vasculitis in the
Western world, is an inflammatory vasculopathy that preferentially
targets the aorta and its extracranial branches. Immune-mediated
tissue injury of arteries supplying the head, neck and upper
extremities leads to severe and life-threatening complications such
as blindness, stroke, and aortic aneurysm. Vasculitic lesions are
transmural granulomatous infiltrates composed of CD4 T cells and
highly activated macrophages. Immune-mediated damage of the vessel
wall results in intimal hyperplasia, luminal occlusion and tissue
ischemia. The immune response in the vessel wall is initiated by a
tissue-resident population of vascular dendritic cells (vDC). CD4 T
cells are key regulators of this response and differentiate into
vasculitic T cells after being instructed by vascular DC.
Pathogenic T-cell responses are guided and shaped by the unique
environment of the blood vessel wall, but the distinctive pathways
driving DC-T cell interactions are yet to be fully elucidated. An
exploration of unique accessory receptor-ligand pairs assigned a
critical role to the Notch-Notch ligand pathway in the initiation
and sustenance of large vessel vasculitis. Notch signaling
components are elevated in peripheral blood of GCA patients and in
tissue biopsies of affected temporal arteries. Notch signaling
inhibition resulted in repressed cellular responses, decreasing CD4
T cell activation markers and T-cell proliferation. Both
IL-17-producing and IFN-γ-producing T cells are expanded in
GCA patients, suggesting that disease-relevant T cells originate
from two distinct functional lineages. The in vivo relevance of
Notch-dependent T cell responses in vascular inflammation was
tested in a humanized mouse model in which human arteries are
engrafted into immuno-deficient mice and human T cells are
adoptively transferred. Blocking of the Notch pathway through the
γ-secretase inhibitor
N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl
ester (DAPT) led to a significant decrease in T-cell recruitment
and formation of vascular wall infiltrates. Disruption of Notch
signaling inhibited in situ T-cell activation, differentially
downregulating IFN-γ and IL-17 production. T cells secreting
the pro-inflammatory cytokine IL-17 appeared more dependent on
Notch signaling than those releasing IFN-γ. In essence,
disrupting Notch activation has profound immunosuppressive effects,
indicating that Notch pathway modulation may provide novel
therapeutic opportunities for large vessel vasculitis
Table of Contents
Table of Contents
2 Chapter One/Introduction
5 Figure 1.1. Innate and adaptive immune responses lead to
vascular damage in
GCA
9 Figure 1.2. Vascular DC shape the arrangement and
composition of T cell
responses in the arterial wall
17 Figure 1.3. Co-signaling overview
22 Figure 1.4. Notch signaling pathway
32 Figure 1.5. Immune cells and vessel wall cells
collaborate in mediating vascular
damage in GCA
35 Table 1. The spectrum of cells and mechanisms involved in
vessel wall damage
in large vessel vasculitis
38 Chapter Two/ TLR-mediated induction of negative
regulatory ligands on
dendritic cells
50 Figure 2.1. TLR3 stimulation reduces the ability of DC to
induce T-cell
proliferation
53 Figure 2.2. TLR3 and TLR4 ligands are equally competent
at inducing DC
maturation and cytokine production
56 Figure 2.3. Induction of T-cell unresponsiveness by
poly(I:C)-treated DC is not
dependent on soluble factors
59 Figure 2.4. Poly(I:C) stimulation preferentially induces
the co-inhibitory ligand
PD-L1
62 Figure 2.5. TLR4 stimulation cannot revert the
TLR3-mediated induction of the
inhibitory ligand PD-L1
65 Figure 2.6. Blockade of PD-L1 restores CD4 T-cell
proliferation
69 Figure 2.7. TLR3-stimulated DC enhance SHP-2
phosphorylation in CD4 T
cells downstream of PD-1/PD-L1 interaction
78 Chapter Three/ Blocking the Notch Pathway Inhibits
Vascular Inflammation
in Large Vessel Vasculitis
92 Figure 3.1. Activated Notch1 is abundant in GCA
arteries
96 Figure 3.2. Expression of Notch1 receptor and the
pro-inflammatory cytokines IL-
17 and IFN-γ by peripheral T cells in GCA
98 Figure 3.3. T cell activation enhances Notch1 surface
expression
101 Figure 3.4. Notch blockade dampens T cell
responses
105 Figure 3.5. γ-secretase treatment suppresses vessel
wall inflammation
109 Figure 3.6. Soluble Jagged1 ligand inhibits T cell
activation and abrogates vessel
wall inflammation
113 Figure 3.7. Notch inhibition attenuates ongoing T cell
inflammatory responses in
the vessel wall
119 Chapter Four/ Notch signaling preferentially regulates
the IL-17 pathway
128 Figure 4.1. IL-17 and IFN-γ production by CD4 T cells
are differentially affected
by Notch inhibition
132 Figure 4.2. Notch signaling regulates CD4 T cells
committed to the Th17 pathway
136 Figure 4.3. Dendritic cell function is unaffected by
γ-secretase inhibition
139 Figure 4.4. Notch1 co-signaling enhances activation of
the STAT3 pathway
145 Chapter Five/Summary
156 References
About this Dissertation
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- Harrison, David G, Emory University
- Weyand, Cornelia, Stanford
- Evavold, Paul Brian, Emory University
- Gewirtz, Andrew T, Emory University
- Goronzy, Jorg, Stanford
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