acute antigens bcr cd40 cd40l tlr4 lps nf b ca 2+ growth genes chronic antigens bcr cd40 tlr4 nf b...
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Acuteantigens
BCR
CD40
CD40L
TLR4
LPS
NFBCa2+
Growth genes
Chronicantigens
BCR
CD40
TLR4
NFBCa2+
Inhibitory genes
Fc2b
Mechanisms of unresponsiveness: Peripheral tolerance in B cells (II): Anergy
Immunogenic signaling Tolerogenic signaling
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The two-signal requirement for T cell activation
Signal 1
Signal 2
TCR
Costimulatory Receptor (CD28)
Microbial antigenpresented by APC
APC
MHC
B7
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The role of co-stimulation in T cell activation
Antigen recognition T cell response
Resting APC:(costimulator-deficient)
Activation of APC Innate immune response
CD28
Activated APC:increased expression of costimulators, secretion of cytokines
No response
T cell proliferation And differentiation
CD28B7
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Regulation of T cell homeostasis during immune responses M
ag
nitu
de o
f T c
ell
resp
ons
e
B7 CTLA-4
B7 CD28
T cell activation
T cell expansion
Activated T cellsexpress CTLA-4
Activated T cells aredeprived of antigen and other stimuli
Apoptosis
Anergy
Surviving memory cells
Time after antigen exposure
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Role of cytokines in suppression of cell-mediated immune responses
Naïve T cellAPC
IL-12
Antigen recognition
T cell proliferationand differentiation
Effector functions of T cells
Effector T cells(TH1)
Activated macrophages
IFN-
Cytokines produced by suppressor
T cells
IL-10 inhibitsFunctions of APCs:IL-12 secretion, B7
expression
TGF- inhibitsT cell
proliferation
IL-4 inhibitsaction of
IFN-
IL-10, TGF- inhibit
macrophage activation
Suppressor T cells
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Tum
or I
ncid
ence
0%
100%RAG-/-
WT
Tumor (Sarcoma) Incidence is Increased in MCA-treated Lymphocyte Deficient Mice
Tum
or S
ize
Host: RAG-/- WT
Tumor:WT origin
RAG-/- origin
Tumors which developed in RAG-/- hosts are REJECTED in WT Recipients
Immunosurveillance: Tumors which Evolve in Lymphocyte Deficient Hosts are Rejected in WT Mice
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Tum
or I
ncid
ence
af
ter
MC
A
Tre
atm
ent
0%
100%
IFNR-/-
WT
Immune Surveillance: Tumor Cell Expression of IFN Receptor is Required for Lymphocyte-Mediated Tumor Rejection
Tum
or S
ize
Host: WT WT WT RAG-/-
WT IFNR-/-
IFNR -/- transfected with IFNR
-------------------Transplanted tumor-------------------------------------IFNR -/- transfected with IFNR
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APCDendritic Cell
CD4 TH1TCR
Class II+
peptide
CD4
CD40L
CD40
Tumor Cell
CTL
Endocytosis/phagocytosis
Ag Processing/presentation of peptides
TCR
CD8
ClassI +peptideB7
CD28
IL-2
Cross-Priming: Induction of Anti-tumor T cell response
Provide TH1 or 2 Help for B cell
Ab Responses
IMMUNE RECOGNITION
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Tumor Cell
CTLGranule exocytosis:Perforin/granzyme
TCR
Fas - F
asL
Effector MechanismsCD8 CTL Can Recognize Class I –peptide Complex and Induce Tumor Lysis and Apoptosis
Class I+ peptide
CD8
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Macrophage
CD4 TH1TCR
Class II+ peptide
CD4
CD40L
CD40
Cytokine-MediatedActivation
IFN-GM-CSF
TNF
TNF (+ other TNF-family members) NO, O2•, proteases
Macrophages are Cell-Mediated Effectors
Effector Mechanisms
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Y
Tumor Cell Y
YYY
Macrophage
ADCC, phagocytosis, release of inflammatory mediators (NO, O2•, proteases, TNF, etc.,)
C3b
Antibody Bound Targets Induce Myeloid Cell Tumor Cyto-toxicity Through Fc Receptors +/or Complement Receptors
Effector Mechanisms
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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 suppression—either dampen
“priming” or avoid/inhibit/resist effector cell function).
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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).
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Model of Innate Recognition and Initiation of the Adaptive Antitumor Immune Response
“danger”= invasion (inflam. response) + “stress” ligands of NKG2D
Amplification of innate and link to adaptive response
Apoptosis provides antigen delivery to DCs Elimination by
adaptive response
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Monoclonal Antibody
Therapeutics in Cancer Rituxan (anti-CD20) • High response rate in B cell
lymphoma (>70%). • 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.
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Functions of Th1 and Th2 cellsType Function Helpful Harmful
Th1
IL-2IFN-TNFα
Activat e macrophag ,esdendrit ic cells
DTH
Tb, fung ,iLeishmaniaa nd otherintracellularbacteria
MSThyroiditisRAIDDMSclerodermapois on ivy
Th2
I -L 4I -L 5I -L 6I -L 10
B cellhelp
dow -n regulat e Th1
class switching
Clearan ce ofantigen /stoxinsHelminths
Allergy
Autoantibody
SLE
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Oligodendrocytes
CD4+ T cells and dying, MHC class II + oligodendrocyte
naked axon (plaque)
Immunopathology of MS
Myelin
Perivascular infiltrate of CD4+ T cells and APCs
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Activated TH1 CD4+ T Cell
CD4+ Cell(TH2 )
CD4+ Cell
(TH0 )
DR3, DR4,,DQ8/gad, insulin peptide
CD2
Macrophage/dendritic cell
Fc R
IFN-
IL-12 CD40L
CD40
α, TCR
IL-1, TNF, LT, NO, PGE-2
B Cell?anti-insulin, GAD ab anti-Mog
IL-4
Immunopathophysiology of Diabetes
?Antibody mediated injury
Dendritic cell/APC
CD40L
IL-4CD40L
CD8+ CTL
FasLperforin
cell death islet cells
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CD4+ T Cell
Activated CD4+ T Cell
TCRα
CD4
CD4
Dermalfibroblast
Plasma CellMHC class II
SmIgSmIg
DR/peptide
IL-1, TNF, TGF-
IL-2, IL-4, IL-5, IL-6Fibroblast proliferation
PGE2, collagen
B Cell
TCR α
IL-2R
IL-2
IFN-
Pathophysiology of Scleroderma
Fibrosis
Anti-scl 70, Ro, La and RFs
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Genetic susceptibility:Complex polygenic Genes Involved:MHC class IIComplement deficiencyMultiple non-MHC (unknown)X-chromosomal (unknown)
CD4+ T cellDriving forceAutoreactive to
self peptides
Autoreactive B cells
IgG autoantibodyProduction
Autoantibody-mediatedDisease
Self-antigen driven
Environmental triggers (drugs, microbes ?)
Other genetic influences ?
SLE pathogenesis
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Two major mechanisms of antibody-mediated tissue injury operating in SLE
Type of antibodyinduced injury
Mechanism of injury Clinicalconsequences
Immune complexformation anddeposition
Ag/Ab complexes depositin vessel walls, causinginflammation by activationof complement cascadeand activation of FcR onphagocytes, mesangialcells, NK cells
glomerulonephritisDermatitisSerositis (arthritis,pleuritis, pericarditis)Diffuse vasculitis
Direct binding to andlysis of cells
Antibody binds to and killscells by activating thecomplement attackcomplex or interactingwith FcR expressingphagocytes or NK cells
Hemolytic anemiaThrombocytopeniaLeukopeniaAplastic anemia
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Serum Sickness develops after injection of soluble foreign antigens
Disease:VasculitisGlomerulitisArthritisPleuritisPericarditisDermatitis
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(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
Why do SLE patients make autoantibodies?
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Why do SLE patients make autoantibodies?
(3) Cross reactivitySLE 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 suppressionSLE might arise as a consequence of abnormalities in regulatory CD4+ or CD8+ T cells.
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• 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.
Evidence that T cells are important in the development of SLE
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MHC/self-peptide CD4
MHC/VCD4
CD4+ Vx T cell APC
Activated autoreactive CD4+TCR Vx TH1 cell
TCR Vx TCR Vx
(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
Induction of CD4+ TH1 mediated autoimmunity:
A paradigm for the pathogenesis of rheumatoid arthritis, multiple sclerosis and
type I diabetes
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CD2
CD4
Macrophage
Rheumatoid factor (RF)
Fc Receptor
DR4/peptide
IL-1, TNF, TGF
CD4+ TH1 Cell
Synthesis of PGE-2, Collagenase, IL-1
inflammation
BONE RESORBTION
Synovial Cell Proliferation
T-Macrophage Interactions Induce Synovial Cell Proliferation and
Activation
α, TCR
CD40L
CD40
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Activated TH1 CD4+ T Cell
CD4+ Cell(TH2 )
CD4+ Cell
(TH0 )
DR4/RA peptide
RF
CD2
MacrophageFc R
IFN-
IL-12 CD40L
CD40
α, TCR
IL-1, TNF, TGFPGE-2, collagenasechemokines
Synovial fibroblast
Endothelial cell
hypothalamus
Fever
Sm Ig
B Cell
RA antigen
Plasma CellRheumatoid factor (RF) (1) Synthesis of
PGE-2, Collagenase, IL-1
(2) synovial cell proliferation
Osteoclast activation
IL-4
Bone and cartilage destruction
Inflammation
Immunopathophysiology of Rheumatoid Arthritis
Vasculitis
Dendritic cell/APC
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Increased synthesis of IL-1, TNF, TGF-, IL-6, PGE2 and Collagenase
Rheumatoid Factors and Immune Complexes Augment the Activation of Macrophages
Rheumatoid factor (RF)
Activated Macrophage
IFN-IL-1
Rheumatoid factor (RF) or immune
complexes
CD2
CD4
Macrophage
Fc Receptor
DR4/peptide
CD4+ TH1 Cell
α, TCR
CD40L
CD40
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CD2
Activated CD4+ T Cell
PrecursorOsteoclast
α, TCR
TNF
TNFR
RANK-L
Soluble RANK Receptor(osteoprotegerin)
Soluble RANK-L
TNFIL-1PGE2
Bone Resorption
RANK
TNF, IL-1 and RANK-L activate osteoclasts to induce bone resorption
MHC class II
CD40CD40
B7
ActivatedOsteoclast
M/dendritic cell
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(a) Block T-APC interaction antibodies to MHC class II, CD4 or the TCR
(b) Decrease T cell activationcyclosporine, anti-CD3, anti-CD28, anti-CD80 (B7), anti-CD40L, CTLA-4 agonist
(e) Inhibit products of T/macrophagesNSAIDs, TNF receptor inhibitors, IL-1 receptor inhibitors
(c) Prevent T cell, B cell or synovial cell proliferationMethotrexate, immuran, cytoxan
(d) Inhibit T cell or APC function steroids, gold, penicillamine
Mechanisms of action of drugs used to treat RA
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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:
• No Autoantibodies “Seronegative”
• Occur at increased prevalence in those with advanced AIDS
• CD8 T cells activated, clonally expanded and sometimes show antigen drive in sites of inflammation
Spondyloarthritis Diseases
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Spondylitis Diseases
• Ankylosing spondylitis
• Reiter’s syndrome / reactive arthritis
• Psoriatic arthritis
• Undifferentiated spondyloarthritis
• Enteropathic arthritis (ulcerative colitis, regional enteritis)
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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:
• No Autoantibodies “Seronegative”
• Occur at increased prevalence in those with advanced AIDS
• CD8 T cells activated, clonally expanded and sometimes show antigen drive in sites of inflammation
Spondyloarthritis Diseases
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Spondylitis Diseases
• Ankylosing spondylitis
• Reiter’s syndrome / reactive arthritis
• Psoriatic arthritis
• Undifferentiated spondyloarthritis
• Enteropathic arthritis (ulcerative colitis, regional enteritis)
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Reiter’s syndrome-Reactive arthritis -Mechanism
Disruption of “tolerance” of autoreactive CD8 T cells likely occurs through a combination of mechanisms:
Activation
• Molecular mimicry - Older theory…T 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
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MHC class I MoleculeSelf Antigenic Peptide
T
Synovial orendon
Fibroblast
Inflammation,Destruction & Fibrosis
Synoviocyte Proliferationand Alteration in Gene
Expression
Angiogenesis
CD8 T-cell Activationand Clonal Expansion
FibroblastActivation
TCD8 -cell
TCR
CognitiveRecognition
Monocyte / macrophage Activation
Lining & Infiltrating
Periosteal new boneformation
CD4 and CD8 T Cell Recruitment
Rx Methotrexate
RxTNF-αblockers