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

The two-signal requirement for T cell activation

Signal 1

Signal 2

TCR

Costimulatory Receptor (CD28)

Microbial antigenpresented by APC

APC

MHC

B7

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

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

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

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

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

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

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

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

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

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).

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).

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

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.

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

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

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

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

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

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

Serum Sickness develops after injection of soluble foreign antigens

Disease:VasculitisGlomerulitisArthritisPleuritisPericarditisDermatitis

(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?

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.

• 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

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

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

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

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

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

(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

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

Spondylitis Diseases

• Ankylosing spondylitis

• Reiter’s syndrome / reactive arthritis

• Psoriatic arthritis

• Undifferentiated spondyloarthritis

• Enteropathic arthritis (ulcerative colitis, regional enteritis)

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

Spondylitis Diseases

• Ankylosing spondylitis

• Reiter’s syndrome / reactive arthritis

• Psoriatic arthritis

• Undifferentiated spondyloarthritis

• Enteropathic arthritis (ulcerative colitis, regional enteritis)

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

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