SELF TOLERANCE

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SELF TOLERANCE

• PHYSIOLOGICAL STATE WHERE THE IMMUNE SYSTEM DOES
  NOT REACT DESTRUCTIVELY AGAINST THE HOST

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Tolerance mechanisms
Ignorance Privilege Dominant
tolerance Anergy Deletion
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SELF-TOLERANCE

• WHY IS KNOWLEDGE LESS ADVANCED THAN THAT OF
  IMMUNITY?
• FAIT ACCOMPLIT AT BIRTH
• ALL OR NOTHING
• CONFLICTS OF DOGMAS
  too much emphasis on in-vitro criteria of
  deletion rather than operational criteria?

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WHY DO WE NOT ATTACK OUR OWN BODY?

• IGNORANCE
• CENTRAL TOLERANCE
• PERIPHERAL TOLERANCE
• LACK OF DANGER-IMMUNE SYSTEM ADAPTED TO REACT TO
  MICROORGANISMS

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TOLERANCE RESEARCH HAS OFTEN USED TRANSPLANT
MODELS

• MARROW
• SKIN
• CO-DOMINANT EXPRESSION OF TRANSPLANTATION
  ANTIGENS WHICH IN PRINCIPLE ARE JUST THE DONORS
  SELF

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Dizygotic cattle twinsthat have shared the same
placenta are tolerant of each others tissues
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CLASSICAL TRANSPLANTATION TOLERANCE
Bone marrow cells from (A x B) F1
Adult (A x B)F1
A strain mouse NEWBORN
A strain ADULT can accept grafts from B
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TOLERANCE SUSCEPTIBILITY DEPENDS UPON THE STAGE
OF DEVELOPMENT OF LYMPHOCYTES-NOT THE AGE OF THE
ANIMAL
RADIATION BONE MARROW CHIMERAS
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CLONAL DELETION IN THE THYMUS

• FUNCTIONAL DATA INCONCLUSIVE
• NEED TO FOLLOW THE FATE OF ANTIGEN-SPECIFIC CELLS

FOLLOW FATE OF T-CELLS RECOGNISING
SELF-SUPERANTIGENS. Certain Vb chains of TCR
are precommitted to react with endogenous
tumour virus products (e.g.Vb6, Vb17). Follow
fate with anti-Vb antisera

• CREATE MICE TRANSGENIC FOR A TCR REACTiVE WITH A
  DEFINED ANTIGEN.
• Follow fate of T-cells with anti-idiotypic
  (clonotypic) antisera.

DELETION
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CENTRAL TOLERANCE BY CLONAL DELETION
T-CELLS WITH TRANSGENIC TCR DELETED IN THE THYMUS
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THYMIC DENDRITIC CELLS ARE EFFICIENT APC FOR
PRODUCING THYMIC DELETION OF T-CELLSUSE OF
THYMIC ORGAN CULTURES CHEMICALLY DEPLETED OF DC
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CAN THYMIC EPITHELIUM PRESENTSELF-ANTIGENS FOR
TOLERANCE?

• ELIMINATE HAEMOPOIETIC COMPONENT
• IRRADIATION
• DEOXYGUANOSINE
• THYMIC RUDIMENTS IN CHICK
• ANTERIOR/POSTERIOR (AB) FROG EMBRYO CHIMERAS
• (Anterior provides thymus and posterior provides
  haemopoietic system)

Answer-YES but less efficient than haemopoietic
cells
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Segregation of tolerance function between DC and
mTEC
From Kyewski
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Gene expression profiles mTEC vs. cTEC
mTEC
cTEC
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Cell type-specific pattern of promiscuous gene
expression
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recessive tolerance (deletion)
scanning
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Pitfalls
activation
effector cells
T
T
release
uptake
mTEC
DC
parenchymal cell
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Autoimmune Polyglandular Syndrome-1 (APS-1)
Autoimmune polyendocrinopathy candidiasis
ectodermal dystrophy (APECED)
disease () target organ
candidate autoantigens (Vogel et al. J.Mol.
Med. 2002) expressed in human or mouse mTEC

hypoparathyroidism (87) parathyroid parathormo
ne, PTH like hormone candidiasis
(80) ? ? adrenal insufficiency
(68) adrenals cytochrome P450 Cyp11a1 alopecea
areata (48) skin hair keratins gonadal
failure (46) testis/ovaries testis specific
antigens keratopathy (20) skin keratins chron
ic hepatitis (15) liver various liver specific
antigens vitiligo (15) skin gp100,
tyrosinase, malabsorption (14) gut e.g.
intestinal fatty acid binding protein pernicious
anemia (11) stomach ATPase pump Hashimotos
thyroiditis (9) thyroid thyroglobulin,
TPO diabetes type 1 (6) pancreas insulin,
GAD67, IA-2
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AVIDITY THRESHOLD MODEL FOR TOLERANCE
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• IPEX- X-LINKED AUTOIMMUNITY-ALLERGIC
  DYSREGULATION SYNDROME
• early onset diabetes, IBD, thyroiditis,
• manifestations of Atopy
• Foxp3 may be the master regulator that guides
  naïve T-cells to become regulatory

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FOXP3 (Scurfin) determines CD4CD25 polarisation
CTLA4 GITR hi CD45RBlo FOXP3 anergic
CD4CD25
Hori, S, Nomura T, Sakaguchi S. Science. 2003
142991057-61. Fontenot JD, Gavin MA, Rudensky
AY.. Nat Immunol. 2003 4330-6. Khattri R, Cox
T, Yasayko SA, Ramsdell F.. Nat Immunol. 2003
4337-42.
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recessive tolerance
scanning
Depletion of CD25/CD4 cells Induction of
gastritis with antigen /IFA ( McHugh Shevach,
2002 )
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None low moderate
high
Affinity
Apoptosis deletion
Positive selection CD4CD25- FoxP3-
Death by neglect
Positive selection CD4CD25 FoxP3
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recessive tolerance
scanning
Depletion of CD25/CD4 cells Induction of
gastritis with antigen /IFA ( McHugh Shevach,
2002 )
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OTHER WAYS OF DEMONSTRATING A ROLE FOR NATURAL
REGULATORY T-CELLS IN PREVENTION OF AUOTIMMUNITY
AND RELATED DISORDERS
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SUPPRESSION IN SELF-TOLERANCE

• .
• MAY BE HARD TO DISTINGUISH FROM EFFECTS OF
  HOMEOSTASIC EXPANSION IN SOME OF THE MODELS
• Gita Stockinger will discuss this in more detail.

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CENTRAL TOLERANCE IN THE B-CELL COMPARTMENT

• ANIMALS FAIL TO MAKE ANTIBODIES TO SELF-ANTIGENS
  BECAUSE OF TOLERANCE IN T-CELLS, B-CELLS OR BOTH.
• B-CELLS ALSO UNDERGO CLONAL DELETION/INACTIVATION
  TO CERTAIN SELF-ANTIGENS.
• Extent determined by ANTIGEN LEVELS, MULTIVALENCY
  AND AFFINITY THRESHOLDS.

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THE USE OF Ig (BCR)-TRANSGENIC MICE TO STUDY
B-CELL TOLERANCE

• WORK OF GOODENOW AND BASTEN.
• CROSS BCR-TRANGENIC STRAIN (ANTI-LYSOZYME) TO
  ANOTHER TRANSGENIC STRAIN EXPRESSING LYSOZYME
  CONSTITUTIVELY
• THE F1 HYBRID STRAIN STILL POSSESS B-CELLS
  EXPRESSING THE TRANSGENIC BCR.
• ONE CANNOT IMMUNISE THESE ANIMALS TO MAKE
  ANTIBODIES TO LYSOZYME EVEN WITH ATTACHMENT TO A
  FOREIGN CARRIER.

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WHAT FORM OF ANTIGEN DETERMINES B-CELL DELETION?

• CELL SURFACE BOUND-MULTIVALENCY
• EVIDENCE FROM BCR-TRANSGENIC MICE TO
  SELF-ANTIGENS KK AND LYSOZYME.
• ENGINEERED CELL-SURFACE FORMS FAR MORE
  DELETIONAL THAN SOLUBLE OR INTRACELLULAR FORMS.

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ANERGY IN B-CELLS

• DOWNREGULATION OF THE BCR
• ALSO TRUE WITH INDUCIBLE PROMOTERS.
• HARD TO REVERSE UNLESS USE STRONG SOURCES OF
  STIMULATION
• REASON
• ABSENCE OF T-CELL HELP
• ABSENCE OF T-CELL DERIVED SIGNALS

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B-cells for certain self-antigens are not deleted
or inactivated

• Use of polyclonal activators or provision of
  T-cell help to detect these cells
• e.g. the complement component C5
• Thyroglobulin

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PERIPHERAL TOLERANCE

• TOLERANCE OCCURRING OUTSIDE THE PRIMARY LYMPHOID
  ORGANS
• DELETION
• ANERGY
• REGULATION
• IGNORANCE

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PROFESSIONAL VERSUS NON-PROFESSIONAL PRESENTATION
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SITE OF SELF-ANTIGEN DETERMINES TOLERANCE
PHENOTYPE
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DELETION IN THE PERIPHERY

• -DEPRIVATION OF GROWTH FACTORS, LACK OF
  CO-STIMULATION
• ACTIVATION INDUCED CELL DEATH
• OFTEN FAS-FAS-LIGAND MEDIATED
• Race between cells acquiring survival factors and
  committing suicide.

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The Balance of Life and Death
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Two Types of Cell Death
Necrosis
Apoptosis
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Physiological functions of apoptosis
Deletion of unwanted cells A Sculpting
structures (e.g. metamorphosis) B Deleting
unneeded structures C Elimination of
autoreactive thymocytes D Downregulation of
immune response E Elimination of tumor cells and
virus infected cells F Controlling cell
numbers (epithelium etc.)
A
B
C
Apoptotic cells
Müllerian duct
Wolffian duct
3 - 5 days
Stem cells
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Two Roads to Death
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The Mitochondrial Pathway
Anti-apoptotic Bcl-2 family member
Pro-apoptotic Bcl-2 family member
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• THE PIVOTAL ROLE OF DENDRITIC CELLS IN T-CELL
  TOLERANCE

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OVERVIEW
DANGER DEATH BY NECROSIS INFLAMMATION COSTIMULATIO
N ADJUVANTICITY 2ND SIGNALS
NO DANGER APOPTOTIC DEATH LACK OF COSTIM. NO 2ND
SIGNALS NO HELP
ACTIVATION INDUCED CELL DEATH
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CD4 T-CELLS CAN HELP OTHER T-CELLS BY LICENSING
DENDRITIC CELLS
NAIVE T-CELLS
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INTER T-CELL CO-OPERATION PREVENTS TOLERANCE
INDUCTION
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IMMUNE DEVIATION
TH0
TH1
TR1
TH?
TH2
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SUPPRESSION
POTENTIALLY REACTIVE T-CELL
SUPPRESSOR T-CELL
?
APC
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• PRIVILEGE.
• IS IT INNATE OR ACQUIRED?

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MATERNO-FOETAL RELATIONS
BABY
PLACENTA
MACROPHAGES WHICH METABOLISE TRYPTOPHAN
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REPROGRAMMING THE IMMUNE SYSTEM

• AUTOIMMUNE DISEASE
• TRANSPLANTATION
• ALLERGY
• SHORT-TERM THERAPY FOR
• LONG-TERM BENEFIT

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TIPPING THE BALANCE IN FAVOUR OF REGULATION
IMMUNITY
TOLERANCE
REGULATORS
EFFECTORS
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BLOCKADE OF CO-RECEPTORS OR OF CO-STIMULATORY
MOLECULES CAN GENERATE DOMINANT TRANSPLANTATION
TOLERANCE
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1985WHAT IS THE CONSEQUENCE TO A TRANSPLANTED
TISSUE OF SHORT-TERM BLOCKADE OF T-CELL ADHESION
RECEPTORS?

• ANTIBODIES TO CD4, CD8, CD40L etc.
• NO EFFECT
• DELAYED REJECTION
• TOLERANCE?

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BLOCKADE OF CD4 WITH MONOCLONAL ANTIBODIES
CD4 T-CELL
CD28
CD40L
CD80
CD40
DENDRITIC CELL
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SHORT-TERM BLOCKADE THROUGH CD40L CAN RESULT IN
TOLERANCE
T-CELL
CD40L
TCR
PEPTIDE
CD40
MHC

DENDRITIC CELLS
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GRAFT B
GRAFT C
S. Qin et al. Eur J Immunol 1987171159
RECIPIENT A
S. Qin et al. J Exp Med 1989169779
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LINKED SUPPRESSION

• TOLERANCE TO GRAFT B
• LEADS TO
• ACCEPTANCE OF GRAFT B x C
• LEADS TO
• TOLERANCE TO GRAFT C

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LINKED SUPPRESSION
(BxC) GRAFT IS NOT REJECTED
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INFECTIOUS TOLERANCE

• FIRST COHORT OF LYMPHOCYTES RENDERED TOLERANT TO
  ANTIGEN
• THIS ENABLES FURTHER COHORTS TO ALSO BECOME
  TOLERANT AS THEY DEVELOP

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(1) SUPPRESSION
POTENTIALLY REACTIVE T-CELL
SUPPRESSOR T-CELL
?
APC
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SUPPRESSION
SUPPRESSOR T-CELL
IMMATURE APC
MATURE APC
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(3) ACQUIRED PRIVILEGE IN THE GRAFT?
(BxC) GRAFT
T-CELLS TOLERANT OF B ANTIGENS ENTER TISSUE AND
PREVENT REJECTION OF B ANTIGENS. THIS PROCESS
ALSO STOPS REJECTION OF C ANTIGENS IN THE SAME
GRAFT
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A ROLE FOR TGFb IN TOLERANCE INDUCTION?
From Stephen Daley, Dunn school
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Regulatory T-cells are present in tolerated skin
grafts
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Graft Survival
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0
0
25
50
75
100
125
Time (days)
Graca L, et a (2002)l. J Exp Med 1951641 (
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WHY IS TOLERANCE LONG TERM?

• ANTIBODY THERAPY PREVENTS GRAFT REJECTION-GRAFT
  HEALS
• GRAFT PROTEINS CONTINUALLY RELEASED
• PROCESSED BY RESTING HOST APC (in the absence of
  danger signals)
• MANY T-CELLS SEEING ANTIGEN IN THIS FORM ARE
  INACTIVATED
• OTHERS ARE INDUCED TO BECOME ABLE TO REGULATE
  (PERSISTENT INCOMPETE SIGNALLING)
• NEW COHORTS OF T-CELLS EXPOSED TO SAME ANTIGENS
  ALSO BECOME REGULATORY (INFECTIOUS TOLERANCE)
• APC (transient) and tissues (long-term) become
  privileged sites which further perpetuate
  tolerance!!

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Drugs in transplantation

• Need drugs that will help-not antagonise
  tolerance.
• Permit activation induced cell-death
• Permit development of regulatory T-cells
• Prevent development of aggressive effector
  function

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Regulatory T-cell
Tissue
CHANGES REDUCED INNATE IL-10, TGFb IDO HO,
CO CHEMOKINES DOWNREGULATED APC PROTECTIVE
GENES OTHER INHIBITORS OF INFLAMMATION
CD4CD25-
CD4CD25
Conferring Privilege
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REPROGRAMMING IN TYPE I DIABETES

• NEW ENGLAND JOUNRAL (IN PRESS)

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