CENTRAL TOLERANCE IS INDUCED AND MAINTAINED IN THE THYMUS

Clonal deletion of self agressive B and T cell clones (not complete)

B AND T CELLS WITH SELF REACTIVITY ARE PRESENT IN THE AVAILABLE PERIPHERAL T CELL REPERTOIRE

PERIPHERAL TOLERANCEMaintenance of self tolerance of T-lymphocytes against tissue-specific self proteins which are not represented in the thymus

Active mechanisms at the level of CD4+ helper T-lymphocytes

AUTOIMMUNE DISEASESDisturbance of tolerance

Misdirected adaptive immunity to healthy cells and tissues

Normal tissue cells do not express MHC class II

NO SIGNAL 1. for CD4+ Th activation

Normal tissue cells do not express co-stimulatory molecules and do not produce T cell differentiating cytokines

NO SIGNAL 2. for CD4+ Th activation

Migration of naive T lymphocytes to normal tissues is limitedAntigen presenting cells are not activated in normal tissues

NO SIGNAL 3. for CD4+ Th activation

PERIPHERAL TISSUES TOLERIZE THEMSELVES

PERIPHERAL TOLERANCE

IMMUNE RESPONSES ARE NOT INITIATED IN THE PERIPHERY

ANERGY – Functional unresponsiveness, no IL-2 secretion

SIGNAL 1 Recognition of auto-antigen on tissue cellSIGNAL 2 No B7 and CD40 expression, no co-stimulation

Tissue resident professional APC are not activated SIGNAL 3 Innate immunity is not activated No inflammation

CLONAL DELETION – Activation induced cell deathRequires persistant high antigen dose Fas – FasL interaction

SUPPRESSION – Activity of other cells Cytokine-mediated balance Effector functions are inhibited by regulatory T cells

CLONAL IGNORANCENo contact with the immune system

Immunologically privileged sites Central nervous system, eye

No recognition in the periphery

MECHANISMS OF PERIPHERAL TOLERANCE

NEGATIVE REGULATION OF THE IMMUNE SYSTEM

NEGATIVE REGULATION IN THE IMMUNE SYSTEM1. Decrease of antigen concentration in the course of the immune response2. Inhibition of B lymphocyte activation - antibody feedback

• Cross linking of BCR with FcRIIB (CD32) by antigen-antibody complex• ITIM-induced negative signaling of B cell activation - phosphatases• B cells without T cell help are excluded from follicles

3. Death of activated T lymphocytes• Passive cell death mediated by the shortage in survival factors (cytokines)• Activation induced FasL expression sensitizes activated T cells for Fas-• mediated apoptosis (AICD)• Activation induced cell death (AICD) is induced by repeated antigenic

stimulation4. Inhibition T lymphocyte activation• Anergy of CD4+ T lymphocytes • Late in the immune response activated T cells express CTLA-4, the ligand of

B74. Suppression by regulatory T lymphocytes

• Counter regulation of Th1 and Th2 cytokines• Production of suppressive cytokines• IL-10 inhibits APC function such as IL-12 secretion and B7 expression• TGF inhibits T-cell proliferation• IL-4 inhibits IFN-mediated functions• IL-10 and TGF inhibit macrophage activation

NEGATIVE REGULATION OF IMMUNE RESPONSES

Days5 10 15 20 25 30

Naive lymphocytes

Number of antigen specific cells

Primary effectors

Secondary effectors

Memory

DIFFERENTIATION

AICD

EXPANSION

AICD

MEMORY

Ia

SS

SS

SS

SS

SS

Ib

SS

SS

IIb1 IIb2/IIb3

S S S SS S

SS

SS

IIIa IIIb

SS

SS

SS

SS

SS

SS

ITIMITAM

S S

IIc

SS

SS

IIa trimerCa2+

Ca2+Ca2+

SS

ITAM

SS

tetramer

-S-S--S-S-

SS

SS

ITAM

SS

SS

SS

SS

SS

SS

poli-Ig receptor

SECRETORY PIECE

ITAM

Iγ-γ

FcγRI (CD64) FcεRIIFcγRII (CD32)

IIIaζ-ζ IIIaζ-γ IIIaγ-γ IIIaβ

α β γ-γ α γ-γ

γ-γ α

FcεRI

FcγRIII (CD16)

IMMUNOGLOBULIN BINDING Fc RECEPTORS

IgG Fc receptors

FcRI

Ig supergene family, MIRR

ITAM

ITIM

NEGATIVE REGULATION OF B LYMPHOCYTES BY IMMUNE COMPLEXES

FcRIIb

Activating receptorITAM

Expression Inhibitory receptorITIM

Expression

Fc receptorok

Ig supergene family BCR* B cell

TCR,* CD3* T cell

FcRIa (CD64)FcRI*

Macrophage, DC (internalization)

FcRIIa (CD32) Macrophage, DC (internalization)

FcRIIb (CD32) B cell

FcRIIIa (CD16) FcRI* vagy *

NK cell (ADCC)

FcRI, FcRI* Mast cell (ADCC)

C-type lectin

FcRIIb (CD23b) FcRIIa (CD23a) B cell

MHC I receptorok

Ig supergene family Human KAR Human KIR NK and T cell

C-típusú lektin Egér KIR

Human NKG2C/D NK and regulatory T cell Human NKG2A/B NK and regulatory T cell

Other receptors

BCR CD22 B cell

CD28 CTLA-4 T cell

MIRR Multisubunit Immune Recognition Receptors The ligand binding and signal transducing subunits are separated, they co-localize in membrane microdomains.

CD28

Activated T cell

CD28 cross linked by B7

Costimulatory molecules also associatewith inhibitory receptors

CTLA-4 binds CD28 with a higher affinity than B7 molecules

/CTLA-4

B7

CD28

T cell

B7

2 2Signal 1 +

Co-stimulationinduces CTLA-4

The lack of signal 2 to the T cell shuts down the T cell response.

Cross-linking of CTLA-4by B7 inhibits co-stimulationand inhibits T cell activation

- - -- -

NEGATIVE REGULATION OF T CELL ACTIVATION BY CTLA-4

CTLA-4

CD28

B7

LATE EXPRESSION

HIGHER AFFINITY TO B7 THAN CD28

TAPC

C D 8 + Tc

F a s

C D 4 + T h 1

F a s L

C D 4 +

T h 1

A P C

B

THE ROLE OF CD4+ T CELLS IN APOPTOSIS

T CELL HOMEOSTASIS SHUT OFF IMMUNE RESPONSES

REGULATORY T CELLS

TregTregCD25IL-2Rα

CTLA4B7 ligand

GITR

MARKERS OF THYMUS DERIVED NATURAL Treg CELLS

CD127IL-7Rα ↓

Treg differentiation, maintenance, functionTranscription factor – many target genesItself is not sufficient to confer suppressive function A TGFβ does not induce regulatory function

FoxP3

CD4+CD25+FOXP3+

REGULATORY T CELLS

FUNCTIONS OF REGULATORY T CELLSFUNCTIONS OF REGULATORY T CELLS

•Maintenance of peripheral tolerance

•Prevention of autoimmunity

•Limiting inflammatory processes (asthma, inflammatory bowel diseases)

•Inhibit protection against infectious diseases

•Limit immune responses to tumors

MECHANISM

Intrinsic and extrinsic regulation

Various inhibitory mechanisms

Cell contacts – Cytokines

Interaction with the target effector T cells

REGULATORY FUNCTION OF REGULATORY T LYMPHOCYTESREGULATORY FUNCTION OF REGULATORY T LYMPHOCYTES

IL-35

Inhibitory cytokines

TGFβ

IL-10

Cytolysis

Metabolic dysregulation Inhibition of dendritic cell maturation

Descreased cytokine production (IL-2)Adenosin around the cell

cAMP transfer

Indolamin2,3-dioxigenaseLAG-3 – CD4 homologTreg : effektor T cell = 1 : 8Treg : DC = 1 : 0,8

THE ROLE OF IL-35 IN THE FUNCTION OF REGULATORY T CELLSTHE ROLE OF IL-35 IN THE FUNCTION OF REGULATORY T CELLS

Induced capability, the effector cell is involved

NOT ONLY A FUNCTION

•The molecular patterns of activated Treg cells are different in the presence and absence of effector cells

•The expression of EBI3 and IL-12α/p35 (IL-35) subunits is increased in the presence of effector T cells

•Treg cells in contact with effector cell act also on effector cells out of contact through IL-35

Initial T cell activation Sensed by Treg cells

Increased suppressive mechanisms

TOLERANCE AND AUTOIMMUNITY

STRONG IMMUNE RESPONSES TO FOREIGN ANTIGENS WHILE SUSTAINED TOLERANCE TOWARD HUMAN MACROMOLECULES

AUTOIMMUNE DISEASES

Complicated multifactorial diseases

No single entity can be identified as the necessary and sufficient cause of a particular disease

Unlucky combination of genetic and environmental factors

Side effect of successfully fighting against infections

Disease HLA serotype

Relatív risk Sex ratioWomen/male

Ankylosing spondylitis B27 87.4 0.3

Acute anterior uveitis B27 10.04 <0.5

Goodpasture’s syndrome DR2 15.9 ~1

Multiple sclerosis DR2 4.8 10

Graves’s disease DR3 3.7 4 - 5

Myasthenia gravis DR3 2.5 ~1

Systemic lupus erythematosus DR3 5.8 10 - 20

Insulin dependent diabetes mellitus

DR3 and DR4

3.2 ~1

Rheumatoid arthritis DR4 4.2 3

Pemphigus vulgaris DR4 14.4 ~1

Hashimoto thyroiditis DR5 3.2 4 - 5

ASSOCIATIONS OF HLA ALLOTYPE WITH SUSCEPTIBILITY TO AUTOIMMUNE DISEASE

Maximum 20% of predisposed people develop the disease environmental factors

• Chronic inflammatory conditions• Repair mechanisms cannot compete with tissue destruction caused by

the immune system• Variety of symptoms and of target tissues • 2 – 3% of the population, females are more commonly affected• Mechanisms of recognition and effector functions are the same as

those acting against pathogens and environmental antigens

• Both genetic and environmental factors are involved in the pre-disposition to autoimmune diseases – HLA class I and II and other genetic factors affect susceptibility

• Runs in families and varies between populations• C1, C2 or C4 deficiency predisposes to systemic lupus erythematosus (SLE)

– Environmental factors• Goodpasture’s syndrome – autoantibodies to type IV collagen,

glomerulonephritis, smokers develop pulmonary hemorrhage as well• Symphathetic ophtalmia – provoked by demage• Infection – Wegener’s syndrome – antibodies to proteinase-3 of neutrophil

granules results in destruction of small blood vessels primarily in the lungAny infection can induce granulocyte activation and exposure of the autoantigen

AUTOIMMUNE DISEASES

TISSUE-SPECIFIC AUTOIMMUNE DISEASESEndocrine glands

• Tissue-specific proteins are not expressed in other cells• Vascularized tissues, secrete hormone to the blood

– Easy access to the immune system• Impaired function of a single type of epithelial cells• Thyroid gland

– Hashimoto’s thyroiditis• no thyroid hormone production – hypothyroid • CD4+ T cells and antibodies against thyroglobulin and microsomal proteins

– Graves’ disease• Antibodies to TSH receptor – hyperthyroid• Negative feedback regulation is not functional• CD4+ Th2 cells and antibodies against the muscle of eye – bulding eyes

• Islets of Langerhans in pancreas– Insulin-dependent diabetes

• T cells against insulin, glutamic acid decarboxylase GAD– Insulin-resistant diabetes

• Antagonistic antibodies to insulin receptor• Adrenal gland

– Addison’s disease – chronic adrenal gland hypofunction• Lymphocyte infiltration

DISEASES MEDIATED BY ANTIBODIES AGAINST CELL SURFACE RECEPTORSType II hypersensitivity

Syndrome Antigen Antibody Consequense

Grave’s disease Thyroid stimulating

hormon receptor

Agonist Hyperthyroidism

Myasthenia gravis Acetylcholine receptor

Antagonist Progressive muscle weakness

Insulin resistant diabetes

Insulin receptor Antagonist Hyperglycemia, ketoacidosis

Hypoglycemia Insulin receptor Agonist Hypoglycemia

Grave’s disease – signaling through the TSH receptor

the disease is transferred to the fetus by antibodies

can be cured by plasmapheresis

Myasthenia gravis – internalization and degradation of the receptor

PITUIARY

Tyroid stimulating hormon

TSH

PITUIARY

Tyroid hormonsT3/T4

HYPERTYROSIS

STIMULATING ANTIBODIES IN GRAVES’ DISEASE

Tyroid hormonsT3 triiodine tyronin

T4 tyroxinTyroglobulin

Folliculus lumen

NEGATIVE FEED BACK

Nerve impulse

Nerve impulse

Internalization

NO Na+ influxNO muscle contraction

MIYSTENIA GRAVIS

BLOCKING AUTO – ANTIBODIES IN MYASTENIA GRAVIS

NEURO-MUSCULAR JUNCTION

Muscle

Acetilcholin receptor

Degradation

InsulinInsulin

cell cell cell cell cell cell

PPaancreatic islet cellsncreatic islet cells

MECHANISM OF AUTOREACTIVITY IN INSULIN-DEPENDENT DIABETESType IV hypersensitivity

AUTOREACTIVE CYTOTOXIC T CELLS KILL INSULIN SECRETING β-CELLS

glucagon Somatostatin108 insulin secreting cells

SYSTEMIC AUTOIMMUN DISEASESAutoreactivity against common components of human cells

• Systemic lupus erythematosus SLE– Type III hypersensitivity– Autoantibodies against cell surface, cytoplasmic, nuclear proteins,

nucleic acid, nucleoprotein particles induce tissue demage– Comon nucleoprotein particles

• Nucleosome• Splicosome• Small cytoplasmic ribonucleoprotein complex – Ro, La

– Soluble cellular antigens bind antibodies and form soluble immune complexes – released form dying, dead cells

– Immune complexes are deposited to blood vessels,kidneys, joints and other tissues

• Rheumatoid arthritis – Type IV hypersensitivity– Cellular response to synovial membrane

• CD4+ and CD8+ T cells, B cells, plasma cells, neutrophils, macrophages• Production of rheuma factors – antibodies to IgG-Fc

FACTORS INVOLVED IN THE PATHOMECHANISM OF AUTOIMMUNE DISEASES

• Lack of AICD – mediated clonal deletion– mutation in Fas or FasL

• Block of anergy– induced by tissue necrosis or local inflammation breaking T cell anergy by increased B7 expression

• Novel Th epitope self reactive B cell activation drug induced hemolytic anemia

• Inefficiency of regulatory T cell function

• Molecular mimicry– cross reactivity of pathogenic and self proteins

• Polyclonal lymphocyte activation– LPS, superantigens

• Immunologically previledged sites Damage of anatomical barriers– Post-traumic uveitis

• Exposure of cryptic antigens, determinants, sub-dominant epitopes Damage of molecular barriers – APC function, pathogenic enzymes

ANY CHANGE DISTURBING THE PHYSIOLOGICAL THRESHOLD

ASSOCIATION OF INFECTION WITH IMMUNE-MEIDATED TISSUE DEMAGE

Infection HLA association Consequence

Group A Streptococcus ? Rheumatic fevercarditis, polya-arthritis

Chlymydia thrachomatis HLA-B27 Reiter’s syndromearthritis

Shigella felxneri Salmonella typhimurium Salmonella enteritidisYersinia enterocoliticaCampylobacter jejuni

HLA-B27 Reactive arthritis

Borella burgdorfei HLA-DR2, DR4 Chronic arthritis in Lyme disease

Type II HYPERSENSITIVITYIgG antibodies bound to cell surface or tissue antigen

• Antigen expressing cells – become sensitive to complement-mediated lysis and/or opsonized phagocytosis

• Frustrated phagocytosis tissue damage

• Antibodies inhibit or stimulate cell functions

• no tissue damage

HYPESENSITIVITY REACTIONS caused by

IMMUNCOMPLEXES

Type II and III

Cell Peptide modified by drug

Th

B

IgG type antibodies

MECHANISMS OF DRUG SENSITIVITY

„Butterfly„ flush on the face - discoid lupus erythematosus (DLE) – skin manifestation systemic lupus erythematosus (SLE)

Chronic inflammation in SLE upper dermis. Vacuolized and disintegrated basal layer, flushing purpura containing erythrocytes.

TYPE III HYPERSENSITIVITY IN SLE

Immunofluorescent staining with anti-complement antibody. IC deposition takes place at the dermal – epidermal border.

Immunofluorescent staining with anti-IgG antibody.

IMMUNE COMPLEX DEPOSITION IN THE SLE SKIN

Glomerulus in lupus nephritis. Lupus nephritis

KIDNEY LESIONS IN RHEUMATIC DISEASES