The Immune System

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Type 1 diabetes
Anti-insulin health

• No cure therapy is insulin for life
  physiologic glycaemic control never achieved

Anti-insulin disease

• Excess morbidity and mortality

• Incidence increasing by 5 every 5 years costs
  1 billion of UK NHS budget

Peakman
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Type 1 diabetes is T cell mediated

• Infiltrating CD4, CD8 T cells
• Anti-T cell therapies are effective
• Islet cell autoantibodies ? disease

CD4 T-cell
CD8 T-cell
TCR
CD4 Treg
Epitope
HLA II
HLA I
APC
Peakman
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The Immune System

• Innate
• Rapid Microbial Defense
• Adaptive Immune System Activation

• Acquired (Adaptive)
• Long-lived Microbial Defense
• Neoplasm surveillance
• Autoimmunity, Transplantation Rejection Atopy

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The Innate Immune System

• Antimicrobial Peptides (e.g., Defensins,
  Cathelicidins)
• Phagocytes (Macrophages, Neutrophils, Monocytes,
  Dendritic Cells)
• Pattern Recognition Receptors
• Alternative Complement System
• NK Cells
• B1B Cells
• Aspects of both the innate and adaptive immune
  system

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Selected Pattern Recognition Receptors Toll-like
Receptors
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Selected Pattern Recognition Receptors Other
Families
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The Adaptive Immune System

• Cell-mediated Immunity (Cytotoxicity)
• T cells
• CD4 (Th1 Th2)
• CD8 (Tc1 Tc2)
• Humoral Immunity (Antibody production)
• B Cells

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Th1 and Th2 CD4 T Cells

• Th1
• IL-12 induces differentiation
• Cytokine ProductionInterferon-?Interleukin-2
• Intracellular Pathogens
• Macrophage Activation
• Delayed Type Hypersensitivity

• Th2
• IL-4 induces differentiation
• Cytokine ProductionInterleukin-4Interleukin-5I
  nterleukin-13
• Extracellular Pathogens
• B Cell activation IgE
• Eosinophil responses
• Immediate Type Hypersensitivity

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T cell signaling molecules and autoimmunity
Human T1D loci (Ref1) MHC ?s 3 Insulin
odds 1.9 CTLA4 odds 1.2 PTPN22 odds 1.7 Cblb
Komeda rat (Yokoi N, Nat Genet, 2002) Pten
Cre-loxP knock-out (Suzuki A, Immunity,
2001) Zap70 Sakaguchi mice (Sakaguchi N,
Nature, 2003)
(Mustelin T, et al. Mol Immunol. 2004)
Concannon P et al. Diabetes. 2005
Oct54(10)2995-3001.
H. Ueda
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B and T Lymphocyte Antigen Receptors

• 2 light chains (? or ?)
• 2 heavy chains (5 isotypes IgG, M, A, D, E)
• 2 Binding sites (Divalent)
• Secreted into circulation
• Binds Soluble Antigen

• 2 Chains ?/? (95) or ?/? (5)
• 1 Binding site (Monovalent)
• Membrane Bound, Not Secreted
• Binds Antigen Complexed with MHC

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HLA
J. Noble
Human Leukocyte Antigen human MHC cell-surface
proteins important in self vs. nonself
distinction present peptide antigens to T cells
CLASS I A,B,C
CLASS II DR,DQ,DP
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DQB10402
? -chain
Leu56?
?-chain
Asp57?
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Hahn, Wucherpfenning et al. Nature Immunology
6490-496, 2005
Topology of Self-peptide/MHC Binding by Ob.1A12
TCR
Autoimmune (MBP PeptideDR2)
Anti-viral (HA PeptideDR1)
HA1.7
Ob.1A12
Red TCRb Yellow TCRa
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Hahn, Wucherpfenning et al. Nature Immunology
6490-496, 2005
Ob.1A12 HA1.7
Anti-viral (HA PeptideDR1)
Autoimmune (MBP PeptideDR2)
Red TCRb Yellow TCRa
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The Human Leukocyte Antigen Complex (6p21.31)
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HLA Class I and II Molecules Have a Distinct
Structure and Function
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Cis and Trans- Class II Dimerization
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HLA-Peptide TCR
NH3
?2 Helix
a1 Helix
CDR1
TCR alpha
CDR3
CDR2
CDR2
CDR3
TCR beta
CDR1
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COO-
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Tetramer for T Cell Analysis
DQ
PEPTIDE
Avidin
DQ
DQ
DQ
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T cell Recognition of Antigen on an APC
Antigen
Endocytosis
CD4 T cell
APC
T Cell Receptor
Peptide
MHC II
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T cell Activation by an Activated APC
IL-1 IL-6 IL-12
IL-12 Receptor
CD4 T cell
CD28
Signal 3
B7
T Cell Receptor
LPS
Signal 2
TLR4
Signal 1
Signal 1 Specificity Signal 2 Activation Signal
3 Differentiation
Peptide
MHC II
Antigen Presenting Cell (APC)
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The 2-Signal Model of Lymphocyte Activation
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APC and T cell Interactions

?Activation
CTLA-4
B7 (CD80/86)
?Activation
CD28
B7 (CD80/86)
CD4 T Cell
Recognition
TCR
MHC II
APC
Adhesion
CD2
CD58 (LFA-3)
?Activation
CD40
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Molecular Interactions of Helper T Cells and APC
CD4 T Cell

CTLA-4

CD28
CD3
p56 lck

CD2
z
z
g
d
e
h
h
CD40L
TCR
C
C
LFA-1
a
b
CD45
V
VLA-1
b
V
a
peptide
B7
LFA-3
B7
MHC II
CD4
ICAM-1
Collagen
APC/ B cell
CD40
CD80/CD86
L. Chess 2002
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T cell activation is regulated by signals derived
from the TCR /CD3/CD4 complex and the CD40L and
CD28/CTLA-4 co-stimulatory molecules

L. Chess 2002
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TCR signaling
TCR
CD4
CD45
CD28
Fathman
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T cell activation induces expression of
functional T cell surface molecules
Induction and activation of B cells APCs
Activated CD4 T cell
Late Activated CD4 T cell
MHC/peptide
CD40L
TCR
TCR
TCR
CD25
Resting CD4 T cell
(-)
()
APC
VLA-1
Qa-1/Vb
Collagen
TCR (anti-Qa-1/Vb)
Migration of sites of inflammation
Activated CD8 T cell
Regulatory CD8 T cell
Down-regulation of Activated CD4 T Cells
L. Chess 2002
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Immunological tolerance

• Definition
• specific immune unresponsiveness to an antigen
  that is induced by exposure of lymphocytes to
  that antigen (tolerogen vs immunogen)
• Significance
• All individuals should be tolerant of their own
• antigens (self-tolerance) breakdown
  --gtautoimmunity
• The induction of tolerance could be exploited to
  treat autoimmune diseases
• Mechanisms of tolerance must first be understood

Fathman
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Mechanisms of unresponsiveness to self antigens

• Central tolerance
• Immature self-reactive T lymphocytes that
  recognize self antigens in the thymus undergo
  negative selection (deletion)
• Peripheral tolerance
• Mature self-reactive T lymphocytes that escape
  central tolerance and recognize self antigens in
  peripheral tissues can be inactivated (anergy),
  killed (deletion) or regulated (suppressed)
• Clonal ignorance
• Mature self-reactive lymphocytes do not respond
  to self antigens
• in non-inflamed settings

Fathman
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The Control of Activated CD4 T Cells by
Regulatory T cells
NKT cells/ CD4CD25 cells CD4CD25- cells
Apoptosis
(- )

TH1 CD4 cells
IL-12/ IFN-g
peptide/APC
(- )
IL-10
IFN-g
IL-4
(- )
Activated CD4 T cells
Resting CD4 T cells
(- )
TH2 CD4 cells
Regulatory immunity CD4/CD8 interactions
CD8 or CD4 suppressor precursor
CD8 or CD4 suppressor effector
L. Chess 2002
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Regulatory T Cell Subsets
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Regulatory T Cells in Autoimmunity
Roncarolo et al. Curr Opinion Immunol 2000
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XPID X-linked Polyendocrinopathy, Immune
dysfunction and DiarrheaFoxp3 Gene Essential
CD4-CD25 T Reg

• XLAAD Autoimmunity Allergic Dysregulation
• Defect in scurfin protein (gene Foxp3/JM2)or
  scurfy mouse
• Immunopathogenesis relates to a deficiency of T
  regulatory cells
• -Scurfy x Nude No Autoimmunity-CD4 T cells
  into Nude Disease-Bone Marrow into irradiated
  No Disease-Mixed Chimera No Disease

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Requirements for the development of an
autoimmune disease
Nature Immunology (9) 759-761 (2001)
Fathman
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Immunopathophysiology of Diabetes
Dendritic cell/ APC
Activated TH1 CD4 T Cell
CD2
CD4 Cell (TH0 )
IL-12
DR3, DR4,,DQ8/insulin peptide
CD40L
IFN-g
a,b, TCR
CD40
IL-4
Macrophage/dendritic cell
CD4 Cell (TH2 )
Fc R
FasL perforin
CD40L
IL-1, TNF, LT, NO, PGE-2
CD8 CTL
IL-4 CD40L
?anti-insulin, GAD ab anti-Mog
B Cell
b cell death
b islet cells
?Antibody mediated injury

L. Chess 2002
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Induction of CD4 TH1 mediated autoimmunity A
paradigm for the pathogenesis of rheumatoid
arthritis, multiple sclerosis and type I diabetes
(1) expansion of CD4, autoreactive TH1 cells
specific for autoantigens (2) migration and
infiltration of these self reactive CD4 TH1
cells into tissues and induction of inflammation
and autoimmunity (3) induction of regulatory
cells which control the growth and activation of
the pathogenic autoreactive repertoire of CD4 T
cells
MHC/self-peptide
CD4
CD4
MHC/Vb
TCR Vbx
TCR Vbx

APC
CD4 Vbx T cell


Activated autoreactive CD4 TCR Vbx TH1 cell
L. Chess 2002
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1984Subset Participants Immunology in Diabetes
Rome