Mechanisms of unresponsiveness: Peripheral tolerance in B cells (II): Anergy

1
Mechanisms of unresponsiveness Peripheral
tolerance in B cells (II) Anergy
Immunogenic signaling
Tolerogenic signaling
2
The two-signal requirement for T cell activation
Microbial antigen presented by APC
TCR
MHC
Signal 1
APC
Signal 2
B7
Costimulatory Receptor (CD28)
3
The role of co-stimulation in T cell activation
Antigen recognition
T cell response
Resting APC (costimulator- deficient)
No response
Activation of APC Innate immune response
Activated APC increased expression of
costimulators, secretion of cytokines
T cell proliferation And differentiation
4
Regulation of T cell homeostasis during immune
responses
Anergy
T cell expansion
Magnitude of T cell response
Apoptosis
Activated T cells express CTLA-4
Surviving memory cells
Activated T cells are deprived of antigen and
other stimuli
T cell activation
Time after antigen exposure
5
Role of cytokines in suppression of
cell-mediated immune responses
Antigen recognition
T cell proliferation and differentiation
Effector functions of T cells
IL-12
Effector T cells (TH1)
Activated macrophages
Naïve T cell
APC
IFN-?
Cytokines produced by suppressor T cells
IL-10 inhibits Functions of APCs IL-12
secretion, B7 expression
TGF-? inhibits T cell proliferation
IL-4 inhibits action of IFN-?
IL-10, TGF-? inhibit macrophage activation
6
Immunosurveillance Tumors which Evolve in
Lymphocyte Deficient Hosts are Rejected in WT
Mice
100
RAG-/- WT
Tumor (Sarcoma) Incidence is Increased in
MCA-treated Lymphocyte Deficient Mice
Tumor Incidence
0
Tumor WT origin RAG-/- origin
Tumors which developed in RAG-/- hosts are
REJECTED in WT Recipients
Tumor Size
Host RAG-/- WT
7
Immune Surveillance Tumor Cell Expression of
IFNg Receptor is Required for Lymphocyte-Mediated
Tumor Rejection
100
IFNgR-/- WT
Tumor Incidence after MCA Treatment
0

-------------------Transplanted
tumor-------------------------------------
IFNgR -/- transfected with IFNgR
IFNgR -/- transfected with IFNgR
WT IFNgR-/-
Tumor Size
Host WT WT WT RAG-/-
8

IMMUNE RECOGNITION
Cross-Priming Induction of Anti-tumor T cell
response
Provide TH1 or 2 Help for B cell Ab
Responses
IL-2
CTL
CD28
CD8
TCR

CD4
CD4 TH1

TCR




CD40L
Class II peptide
ClassI peptide
Tumor Cell
B7
CD40
APC Dendritic Cell
Endocytosis/ phagocytosis
Ag Processing/ presentation of peptides
9
Effector Mechanisms CD8 CTL Can Recognize
Class I peptide Complex and Induce Tumor Lysis
and Apoptosis
CD8
CTL
Granule exocytosis Perforin/granzyme

TCR

Class I peptide
Fas - FasL
Tumor Cell
10
Effector Mechanisms
Macrophages are Cell-Mediated Effectors
TNF ( other TNF-family members) NO, O2,
proteases
CD4
CD4 TH1

TCR
CD40L


Class II peptide
Cytokine- Mediated Activation IFN-g GM-CSF TNF
CD40
Macrophage
11
Effector Mechanisms
Antibody Bound Targets Induce Myeloid Cell Tumor
Cyto- toxicity Through Fc Receptors /or
Complement Receptors
Y
Y
Y
Y
Tumor Cell
ADCC, phagocytosis, release of inflammatory
mediators (NO, O2, proteases, TNF, etc.,)
Y
C3b
CR1
FcR
Macrophage
12
Tumor Evasion Two Separate Problems

• Tumor antigens are not recognized by immune
  response-poorly immunogenic
• (Immunologically ignorant).
• Tumors are resistant to or inhibit immune
  cytotoxic responses.
• (active suppressioneither dampen priming or
  avoid/inhibit/resist effector cell function).

13
Strategies for induction of anti-tumor Immune
Responses

• -Passive-
• Adoptive transfer of T cells Antigenic specific
  T cell clones-requires HLA-restricted
  customized therapy or cytokine-enhanced
  antigen-non-specific T cells (LAK cells). Has
  worked for EBV lymphoproliferative disorders.
• Monoclonal and engineered antibodies
• 1. Humanized/chimeric mAbs Herceptin
  (anti-HER2), Rituxan (anti-CD20), anti-idiotype
  (custom therapy), anti-EGFR (Erbitux), CAMPATH
  (anti-CD52), anti-VEGF (targets neovasculature,
  Avastin).
• 2. Immune conjugates (smart bombs) mAb-toxin
  (Mylotarg anti-CD33 calicheamicin), mAb-chemo,
  mAb-isotope (anti-CD20 Zevalin and Bexxar).

14
Model of Innate Recognition and Initiation of
the Adaptive Antitumor Immune Response
Amplification of innate and link to adaptive
response
danger invasion (inflam. response) stress
ligands of NKG2D
Apoptosis provides antigen delivery to DCs
Elimination by adaptive response
15
Monoclonal Antibody Therapeutics in Cancer

• Rituxan (anti-CD20)
• High response rate in B cell lymphoma (gt70).
  
• Synergy with chemotherapy or XRT.
• Recognizes B cell marker regulating B cell
  activation.
• Induces growth arrest/apoptosis in vitro.

• Herceptin (anti-HER2)
• Lower response rate in breast cancer (15).
• Synergy with chemo (60) or XRT.
• Recognizes EGF-like receptor regulating cellular
  proliferation (ERBB2).
• Induces growth arrest/apoptosis in vitro.

16
Functions of Th1 and Th2 cells
17
Immunopathology of MS

Perivascular infiltrate of CD4 T cells and APCs
CD4 T cells and dying, MHC class II
oligodendrocyte
Myelin
naked axon

(plaque)
Oligodendrocytes
18
Immunopathophysiology of Diabetes
Dendritic cell/ APC
Activated TH1 CD4 T Cell
CD2
CD4 Cell (TH0 )
IL-12
DR3, DR4,,DQ8/gad, 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

19
Pathophysiology of Scleroderma
DR/peptide
TCRa,b


CD4 T Cell
CD4
IL-1, TNF, TGF-b
Dermal fibroblast
IL-2
TCR a,b

IFN-g
IL-2R
CD4
Activated CD4 T Cell
Fibroblast proliferation

IL-2, IL-4, IL-5, IL-6
PGE2, collagen
Fibrosis
SmIg
SmIg
B Cell
Anti-scl 70, Ro, La and RFs
MHC class II
Plasma Cell
20
SLE pathogenesis
Environmental triggers (drugs, microbes ?)
Genetic susceptibility Complex polygenic Genes
Involved MHC class II Complement
deficiency Multiple non-MHC (unknown) X-chromosoma
l (unknown)
Self-antigen driven
Other genetic influences ?
21
Two major mechanisms of antibody-mediated tissue
injury operating in SLE
22
Serum Sickness develops after injection of
soluble foreign antigens
23
Why do SLE patients make autoantibodies?
(1) Anti-self immunity abrogation of self
tolerance SLE might be the result of
insufficient elimination of autoreactive T cell
clones in the thymus or periphery. This might
result in such autoreactive T cells being
released into the peripheral circulation and
causing the autoimmune features of the
disease (2) Hidden antigens The nuclear and
cytoplasmic antigens that are associated with
autoimmunity are not commonly exposed to the
immune system. If such antigens (dsDNA, for
example) are liberated during cellular turnover,
they may incite an immune response. Thereafter,
further release of such antigens might form the
nidus for IC
24
Why do SLE patients make autoantibodies?
(3) Cross reactivity SLE might be a disease
caused by an unknown pathogen such as a virus or
a bacterium. The interaction of pathogen derived
peptides with a susceptible HLA haplotype may
elicit "autoimmune" diseases by activating
pathogenic T cells. Such a pathogen has not been
identified in SLE, but no feature of the disease
suggests that this could not be the etiology.
(4) Abnormal regulation failure of
suppression SLE might arise as a consequence of
abnormalities in regulatory CD4 or CD8 T cells.

25
Evidence that T cells are important in the
development of SLE
The pathogenic anti-DNA antibodies in SLE are
high affinity IgG molecules. Because it is
known that class switching to IgG as well as
somatic mutation and affinity maturation
requires T cells we infer that anti-DNA
antibody-producing B cells are expanded in SLE by
a process that mimics the normal CD4 T
cell-dependent responses, involving common
mechanisms of somatic mutation, affinity
maturation, and IgM to IgG class switching.
The MHC class II restriction and the known
association of DR2 and DR3 with susceptibility
to SLE also strongly point to a predominant role
CD4 T cells in the induction of autoimmunity in
SLE. Finally, animal models of SLE are
effectively treated with molecules which block
key functions of CD4 T cells.
26
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 and cytokines which control the growth and
activation of the pathogenic autoreactive 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
27
T-Macrophage Interactions Induce Synovial Cell
Proliferation and Activation
DR4/peptide
CD2
a,b, TCR
Fc Receptor
CD4 TH1 Cell
CD4
Rheumatoid factor (RF)
CD40L
Macrophage
IL-1, TNF, TGFb
BONE RESORBTION
CD40
inflammation
Synthesis of PGE-2, Collagenase, IL-1
Synovial Cell Proliferation
28
Immunopathophysiology of Rheumatoid Arthritis
Dendritic cell/ APC
Activated TH1 CD4 T Cell
CD2
CD4 Cell (TH0 )
IL-12
DR4/RA peptide
CD40L
IFN-g
a,b, TCR
CD40
IL-4
RF
Macrophage
Sm Ig
CD4 Cell (TH2 )
Fc R
PGE-2, collagenase chemokines
RA antigen
IL-1, TNF, TGFb
B Cell
Osteoclast activation
Synovial fibroblast
Endothelial cell
Rheumatoid factor (RF)
Plasma Cell
(1) Synthesis of PGE-2, Collagenase, IL-1 (2)
synovial cell proliferation
Bone and cartilage destruction
hypothalamus
Vasculitis
Fever

29
Rheumatoid Factors and Immune Complexes Augment
the Activation of Macrophages
DR4/peptide
CD2
a,b, TCR
Fc Receptor
CD4 TH1 Cell
Rheumatoid factor (RF) or immune complexes
CD4
CD40L
Macrophage

IFN-g IL-1
CD40
Increased synthesis of IL-1, TNF, TGF-b, IL-6,
PGE2 and Collagenase
Rheumatoid factor (RF)
Activated Macrophage
30
TNF, IL-1 and RANK-L activate osteoclasts to
induce bone resorption
CD2
a,b, TCR
Activated CD4 T Cell
Mf/dendritic cell
RANK-L
CD40
TNF
CD40
Soluble RANK-L
B7
MHC class II
TNFR
Soluble RANK Receptor (osteoprotegerin)
RANK
TNF IL-1 PGE2
Precursor Osteoclast
Bone Resorption
Activated Osteoclast
31
Mechanisms of action of drugs used to treat RA
(a) Block T-APC interaction antibodies to MHC
class II, CD4 or the TCR (b) Decrease T cell
activation cyclosporine, anti-CD3, anti-CD28,
anti-CD80 (B7), anti-CD40L, CTLA-4 agonist (e)
Inhibit products of T/macrophages NSAIDs, TNF
receptor inhibitors, IL-1 receptor
inhibitors (c) Prevent T cell, B cell or
synovial cell proliferation Methotrexate,
immuran, cytoxan (d) Inhibit T cell or APC
function steroids, gold, penicillamine
32
Spondyloarthritis Diseases
2. Genetic- Susceptibility to develop disease is
associated with inheritance of certain MHC class
I alleles, notably HLA-B27
3. Pathogenesis- CD8 T cells are centrally
implicated while CD4 T cells or B cells
are not essential as shown by MHC class I HLA
associations, plus

• Occur at increased prevalence in those with
  advanced AIDS

• No Autoantibodies Seronegative

• CD8 T cells activated, clonally expanded and
  sometimes show antigen drive in sites of
  inflammation

33
Spondylitis Diseases

• Ankylosing spondylitis
• Reiters syndrome / reactive arthritis
• Psoriatic arthritis
• Undifferentiated spondyloarthritis
• Enteropathic arthritis (ulcerative colitis,
  regional enteritis)

34
Spondyloarthritis Diseases
2. Genetic- Susceptibility to develop disease is
associated with inheritance of certain MHC class
I alleles, notably HLA-B27
3. Pathogenesis- CD8 T cells are centrally
implicated while CD4 T cells or B cells
are not essential as shown by MHC class I HLA
associations, plus

• Occur at increased prevalence in those with
  advanced AIDS

• No Autoantibodies Seronegative

• CD8 T cells activated, clonally expanded and
  sometimes show antigen drive in sites of
  inflammation

35
Spondylitis Diseases

• Ankylosing spondylitis
• Reiters syndrome / reactive arthritis
• Psoriatic arthritis
• Undifferentiated spondyloarthritis
• Enteropathic arthritis (ulcerative colitis,
  regional enteritis)

36
Reiters syndrome-Reactive arthritis -Mechanism
Activation
Disruption of tolerance of autoreactive CD8 T
cells likely occurs through a combination of
mechanisms

• Molecular mimicry - Older theoryT cell clones
  involved in attack on microorganisms expand and
  initiate attack on cells expressing target
  proteins that contain peptides that mimic the
  amino acid sequence found in the microorganisms

• Provision of co-stimulatory signals by activated
  dendritic cells and macrophages in initial immune
  response to infection disrupts anergic or
  unreactive state of T cells

• CD8 T cells express NK and other receptors that
  foster the activation of these cells by danger
  signals recognized by innate immune system
  receptors

37
Rx Methotrexate
MHC class I Molecule

T


Rx TNF-a blockers