Immunological tolerance

IMMUNOLOGICAL TOLERANCEJINTANA CHATAROOPWIJIT9 DECEMBER 2016

DEFINITION

• Tolerance : Unresponsiveness to antigen that is induced by previous exposure to that antigen

• Inherent property of immune system• Response against foreign antigen (nonself)

without attacking host (self)• Specific lymphocyte + Antigen --> activated

lymphocyte --> immune responses or tolerance ( inactivation/elimination )

DEFINITION

• Tolerogens/Tolerogenic antigens : antigens that induced tolerance

• Self-tolerance : Tolerance to self antigens• Autoimmunity : Failure of self-tolerance -->

immune reaction against autologous antigens

PHYSIOPATHOLOGY OF IMMUNE TOLERANCE-RELATED DISEASE

• Complex• Influenced by

• Genetic susceptibility• Route of exposure• Antigen dose• Time of exposure• Structural characteristics of allergen and antigen• Coexposure with stimulators of innate immune response ex.

Infections or commensal bacteria

TOLERANCE

1. Central Tolerance2. Peripheral Tolerance

CENTRAL TOLERANCE

• First step of tolerance during maturation in thymus

• Prethymic T cells enter thymus and reach subcapsular region --> proliferate as large lymphoblast

CENTRAL TOLERANCE

• Maturing cells move deeper into cortex and adhere to cortical epithelial cells ( increased in expression of CD3, CD4, CD8 and TCR )

• T cell receptors (TCRs) on thymocytes are exposed to MHC molecules through these contact

CENTRAL TOLERANCE

• TCRs + autoantigens (medullary thymic epithelial cells, interdigitating cells and macrophage at corticomedullary junction) --> deleted

• Cells expressing CD4 or CD8 --> periphery

FACTORS TO INDUCE NEGATIVE SELECTION OF SELF REACTIVE THYMOCYTE (INTRATHYMIC SELECTION)• Not known• Possible factors

• Affinity of antigen recognition• Type of antigen-presenting cells presenting the antigen• Locally availability of cytokine in thymus• Presence of antigen in thymus ( local or delivery by

blood )• Affinity of thymocyte T cell receptors (TCRs) to

recognize antigen

AIRE ( AUTOIMMUNE RESPONSE ELEMENT)

• Transcription factor controlling expression of some organ-specific "peripheral antigens" in thymus

• Component of multiple protein complex• Function : Transcriptional regulator to

promote expression of selected tissue-restricted antigen in thymus

AUTOIMMUNE POLYENDOCRINE SYNDROME TYPE 1 (APS1) OR AUTOIMMUNE POLYENDOCRINOPATHY-CANDIDIASIS-ECTODERMAL DYSTROPHY/DYSPLASIA (APECED)

• In mouse model : knockout of AIRE gene• In mice : low level several proteins in

medullary thymic epithelial cells in peripheral organs ex. pancreatic insulin

• Characterized by antibody and lymphocyte-mediated injury to multiple endocrine organs ( parathyroids, adrenals and pancreatic islet )

PATHWAY OF APOPTOSIS

NECROSIS VS APOPTOSIS

TWO SIGNAL MODEL : ANERGY

Signal 1Recognition by

helper lymphocyte

No YesTarget

lymphocyte(Naive CD4 T

cell)Signal 2

APC + costimulator molecules

-->Costimulatory

signal

Signal1 : TcR bind their peptide/class II MHC complex

REGULATION OF T CELL RESPONSES BY INHIBITORY RECEPTORS

• Balance between engagement of activating and inhibitory receptors --> outcome of antigen recognition by T cells particularly CD4+ cells

• Inhibitory receptors with physiologic self-tolerance : CTLA-4 and PD-1

CTLA-4

• Negative regulator of adaptive immune responses

• Bind to B7 (CD80 and CD86) costimulatory molecules on APCs

CTLA-4

CTLA-4

• Knockout mice lacking CTLA-4 --> uncontrolled lymphocyte activation with massive enlarge lymph node and spleen and fatal multiorgan lymphatic infiltration : autoimmunity

• Failure of peripheral tolerance and severe T cell mediated disease

CTLA-4

• Animal model : blocking of CTL-4 with antibodies --> autoimmune disease ex. encephalomyelitis

• In human : Polymorphism in CTLA-4 gene : type 1 diabetes and Graves' disease

ACTION OF CTLA-4

• Low on most T cells until cells are activated by antigen

• Inhibiting activation of naive T cells• Express on regulatory T cells

THERAPEUTIC APPLICATION

• Blocking CTLA-4 --> increased immune responses to tumor

• Anti-CTLA-4 antibody : approved for advance melanomas

PD-1

• Programmed cell death 1• Immunoreceptor tyrosine-based inhibitory

motif-containing receptor• Express on T cell activation

PD-1

• Recognized 2 ligands1. PD-L1 : expressed on APCs and many other

tissue cells2. PD-L2 : expressed mainly on APCs

PD-1

• Important in terminating peripheral responses of effector T cell esp. CD8+ cell

• May not be required for function of regulatory T cells

PD-1

• Engagement with ligand --> • Inactivation of T cells• Inhibit IL-2 production• May play role in suppressive function of

Treg cells

PD-1

• In mice : PD-1 knocked out --> autoimmune diseases ex. Lupus-like kidney disease and arthritis

• Autoimmune disorder in Pd-1 knockout mice less severe than CTLA-4 knockouts

A. Direct deletion of immune effector : expression of death-inducing ligand

B. Direct tolerization effector T cells : suppressive cytokines released by tissue cells

C. Suppression effector T cells by regulatory T cells

D. Tolerization of host T cells by tolerizing dendritic cells

E. Ignorance : spatial seperation of T cells and tissue cells ex. Basement membranes

F. Immune priviledge

IMMUNE PRIVILEDGE

• Certain site in body tolerate induction of antigen without eliciting inflammatory immune response

• Maybe for protect vital structures from potentially damaging effects

• Sites : brain, anterior chamber of eyes, placenta, fetus, testes

IMMUNE PRIVILEDGE : FETUS

• Express MHC derived from both parents • Peripheral tolerance of mother to fetus -->

fetal survival• Cells of villous trophoblast lack expression of

MHC class I

IMMUNE PRIVILEDGE : FETUS

• Increase expression of non-classical MHC molecule ex. HLA-G : inhibitory receptor

• Immune deviation to Th2• Increase expression of FasL at placenta

IMMUNE PRIVILEDGE : EYE AND BRIAN

• Limit capacity for regeneration• Immune response in these area could have

devastating effect on individual• Low or no expression of classical MHC class Ia

protein on cell• "Sympathetic ophthalmia"

IMMUNE PRIVILEDGE : POSSIBLE MECHANISM

• Limit lymphatic drainage• Cytokine : inhibition of inflammation• TNF-beta and MIF(migration inhibitory

factor) : inhibition of NK cell mediated cytolytic activity

NATURALLY OCCURING CD4+CD25+FOXP3+ REGULATORY T CELLS

• in healthy : <5% of CD3+CD4+ population• Expression of high levels of alpha chain of

CD25, IL-2 receptor• Hypothesis for generation of Treg cells1. From thymus : specific for self-peptides 2. From naive T cells in periphery : required for

environmental antigen/allergen specific T cells

NATURALLY OCCURING CD4+CD25+FOXP3+ REGULATORY T CELLS

• TNFRSF18/GITR(glucocorticoid-induced tumor necrosis factor receptor family related-gene

• Expressed by activated Treg cells• Be trigger : role in resistance to Treg cell

mediated-suppresion

NATURALLY OCCURING CD4+CD25+FOXP3+ REGULATORY T CELLS

• CD103 (alphaEbeta7)• CD122 (beta chain of IL-2 receptor)• Both highly expressed on Treg cells• Correlated with their suppressive activity

NATURALLY OCCURING CD4+CD25+FOXP3+ REGULATORY T CELLS

• Other proposed markers• Certain chemokine receptors• TLRS• Membrane-bound TGF-beta• Neuropilin 1 ( NRP1 )• Lymphocyte activation gene ( LAG3 )• Granzyme

NATURALLY OCCURING CD4+CD25+FOXP3+ REGULATORY T CELLS

• Additional marker from gene arrays• GPR83 : G protein-coupled receptor 83• ECM1 : extracellular maxtrix 1• IKZF2 : IKAROS family zinc finger 2-

helios

REGULATORY T CELL GENERATION

• Augmented by• FOXP3+ T reg cells• Low doses of pathogen-derived molecules :

filamentous, hemagglutinin • Exogenous signals : histamine, adenosine,

vitamin D3 metabolites• Retinoic acid

REGULATORY T CELL GENERATION : RETINOIC ACID

• Balance of inflammatory Th17 cells and suppressive Treg cells by Th17 cells

• Enhancing expression of FOXP3 through STAT3/STAT5 independent signaling pathway

REGULATORY T LYMPHOCYTE

• Mostly express high levels of IL-2 receptor alpha chain (CD25)

• Transcription factor for development and function : FOXP3

FORKHEAD WINGED TRANSCRIPTION FACTOR : FOXP3

• In mice : expressed by naturally occuring Treg cells

• In humans : upregulation in all activated T cells

• Required for development and function of naturally occuring Treg cells

FORKHEAD WINGED TRANSCRIPTION FACTOR : FOXP3• Directly interact with RUNX1( runt-related

transcription factor 1)• RUNX1( runt-related transcription factor 1)

• Impair expression of IL-2 and IFN-gamma• Exert suppressive activity• In murine : maintain high level of FOXP3

expression

FORKHEAD WINGED TRANSCRIPTION FACTOR : FOXP3

• Induction of RUNX1 and RUNX3 by TGF-beta : generation and suppresive function of induced Treg cells

• RUNX1 and RUNX3 bind to FOXP3 promotor : expressing functional Treg cells

FORKHEAD WINGED TRANSCRIPTION FACTOR : FOXP3

• Leucine-rich repeat-containing 32 receptor (LRRC32 or GARP) : key receptor to control FOXP3 levels in naturally occurring Treg cells through positive-feedback loop

FORKHEAD WINGED TRANSCRIPTION FACTOR : FOXP3

• Cytokines : IL-2, IL-10, TGF-beta• Surface markers : CD25, CTLA4, CD103, GITR,

NRP1, latency-associated peptide (LAP)

FORKHEAD WINGED TRANSCRIPTION FACTOR : FOXP3

• ICOS+FOXP3+ Treg cells use IL-10 and TGF-beta to suppress dendritric cells and T cells function

• ICOS-FOXP3+ Treg cells express TGF-beta• Marker to differentiate between human

regulatory and activated effector T cell : alpha chain of IL-7R (CD127)

MUTATION : DIMINISH FUNCTION

• X-linked autoimmune and allergic dysregulation syndrome (XLAAD)

• Immune dysregulation, polyendocrinapathy, enteropathy, X-linked syndrome (IPEX)

IMMUNE DYSREGULATION, POLYENDOCRINAPATHY, ENTEROPATHY, X-LINKED SYNDROME : IPEX

• Rare autoimmune disease• Mutation of FOXP3 gene• Associated with deficiency of regulatory T

cells• Significant skewing of T lymphocyte toward

Th2 phenotype

IMMUNE DYSREGULATION, POLYENDOCRINAPATHY, ENTEROPATHY, X-LINKED SYNDROME : IPEX

• Autoimmunity• Severe atopy : eczema, food allergy• Eosinophillic inflammation

REGULATORY T CELL GENERATION

• Immune response of memory T cells : essential for inflammation and immune regulation processes in diseases ex. allergic rhinitis, asthma, atopic dermatitis

GENERATION AND MAINTAINANCE OF REGULATORY T CELLS

• Regulatory T cell1. Thymic / natural regulatory T cells2. Peripheral / adaptive / inducible

SUBSETS OF REGULATORY T CELLS

MECHANISM OF ACTION OF REGULATORY T CELLS

• Directly suppress B cell activation• Inhibit proliferation and differentiation of NK

cells• Production of immunosuppresive cytokine ( IL-

10 and TGF-beta )• Reduced ability of APCs to stimulate T cells• Consumption of IL-2

TRANSFORMING GROWTH FACTOR-BETA (TGF-BETA)

• Tumor product• Promote survival of tumor cells in vitro• Type : 1-3• Mostly : TGF-beta1

TRANSFORMING GROWTH FACTOR-BETA1 (TGF-BETA1)

• Produced by CD4+ regulatory T cells, activated macrophages and other cells

• Synthesized as inactive precursor • Proteolytically cleaved in Golgi complex and

form homodimer• Mature form is secreted in latent form in

associated with other polypeptides

TRANSFORMING GROWTH FACTOR-BETA 1 (TGF-BETA1)

• In mice : Suppress airway disease • Target cell : T cells• Association with airway inflammatiom

• Maintain tolerance esp. Oral tolerance• Inhibit proliferation , differentiation and

survival of B and T lymphocyte• Inhibit immunoglobulin isotype switching and

promote differentiation of IgA secreting plasma

ROLE OF TRANSFORMING GROWTH FACTOR-BETA (TGF-BETA)

• Promote differentiation of Langerhan cells and DCs with immature phenotype

• In mast cell : promote chemotaxis but inhibit expression of high-affinity receptor for Fc fragment of IgE

• Inhibit human Th2 response in vitro

ROLE OF TRANSFORMING GROWTH FACTOR-BETA (TGF-BETA)

ROLE OF TRANSFORMING GROWTH FACTOR-BETA (TGF-BETA)

• Regulate differentiation of functionally distinct subsets of T cells

• Promote tissue repair after local immune and inflammatory reaction subside

INTERLEUKIN-10

• Control of allergy and asthma• Synthesized by B cells, monocyte, DCs NK

cells and T cells• Inhibit proinflammatory cytokine production

TH1 and Th2 cell activation

INTERLEUKIN-10

• In T cells : IL-10 receptor-associated tyrosine kinase 2 (TYK2) - constitutive reservoir for protein tyrosine phosphatase nonreceptor 6 (PTPN6/SHP1)

• PRPN6 rapidly binds to CD28 and ICOS costimulatory receptors and dephosphorylates them within minutes

INTERLEUKIN-10

• Member of family of heterodimeric cytokines : IL-22, IL-27 and others

• Consist of two chains• IL-10 receptor belongs to type II cytokine

receptor family

INTERLEUKIN-10

• Associate with JAK1 and TYK2 Janus family kinase and activate STAT3

• Produced by activated macrophage and dendritic cells, regulatory T cell, TH1 and TH2 cells and some B lymphocyte

ROLE OF INTERLEUKIN-10

• Inhibit expression of costimulators and class II molecule on dendritic cells and macrophage --> inactivation

• Control of innate immune reactions and cell-mediated immunity

• Inhibit production of IL-12 by activated dendritic cells and macrophage

MUTATION INTERLEUKIN-10 RECEPTOR

• Rare inherited autoimmune disease• Severe colitis

FACTORS FOR DETERMINE IMMUNOGENICITY AND TOLEROGENICITY OF PROTEIN ANTIGEN

B LYMPHOCYTE TOLERANCE

• Maintain unresponsiveness to thymus independent self antigens (polysaccharide and lipid)

• Prevent antibody responses to protein antigens

CENTRAL TOLERANCE IN B CELLS

PERIPHERAL TOLERANCE IN B CELLS

“Thank you.”