Chapter16 Immunological Tolerance

Innate Immunity and adaptive immunity

Review . Classification of Immunity Humoral immunity and Cell-mediated immunity

Immune response

Immune response

Effect of Humoral Immunity

Immune response

Effect of cell-mediated immunity IL-12 CD4 Th1 IL-4 CD4+Th2 CTL

Antigen recognition and T activation T cell expansion and differentiation Differentiated effector T cells enter circulation Effector T cells encounter antigen in peripheral tissues Effector function of T cells

Immune response and Immunologic tolerance Immunogenic antigens: antigens that induce immune response Tolerogenic antigens: antigens that induce immunologic tolerance

Chapter16 Immunological Tolerance

Contents Introduction The discovery and type of Immunologic Tolerance The conditions inducing Immunologic Tolerance Mechanisms of Immunologic Tolerance The significance and clinical application of Immunologic Tolerance

Introduction Immunologic tolerance: A type of specific unresponsiveness to an antigen induced by the exposure of specific lymphocytes to that antigen, but response to other antigens normally. Tolerogens: antigens that induce tolerance

General features of Immunologic tolerance Specificity : specific unresponsiveness to an antigen, but response to other antigens Memory : secondary unresponsiveness only to same antigen ,but not to other antigens Induction : Its formation needs induction of antigen by the exposure of specific lymphocytes with a time lag

Difference among Immuologic tolerance , immunodeficiency& immunosuppression Immunodeficiency: any condition in which there is deficiency in the production of humoral and /or cell-mediated immunity---non-specificity to Ag Immunosuppression: The suppression of immune responses to antigens. This can be achieved by various means, including physical, chemical factors ----non-specificity to Ag

Section I The discovery and type of Immunologic Tolerance

I. Discovery of immunologic tolerance Owen first observed immunologic tolerance in Dizygotic bovine twin in 1945--- Medawar induced successfully immunologic tolerance in neonate period mice in 1955

Owen first observed phenomenon of immunologic tolerance in Dizygotic bovine twin in 1945 Graft of Skin From A to B or From B to A No rejection Self –tolerance Suggested by Burnet Need for tissue and organ graft drove the curiosity to understand the mechanisms of tolerance. The observations a zoologist, Owens, that Dizygotic bovine twins could accept grafts from each other but their siblings from other pregnancies could not tolerate such grafts led Medawar to perform a series of experiments to induce tolerance in mice.

Medawar induced successfully immunologic tolerance in neonate period mice in 1955 Induced tolerance

Immunologic features of tolerance It is an antigen-induced, active process it possesses specificity It possesses immunologic memory A kind of special immune response Induction of tolerance is very similar to induction of an immune response. Immunologic features of tolerance: Tolerance is different from non-specific immunosuppression, and immunodeficiency. It is an active antigen dependent process in response to the antigen. Like immune response tolerance is specific and like immunological memory, it can exist in T-cell, B cells or both and like immunological memory, tolerance at the T cell level is longer lasting than tolerance at the B cell level.

for discovery of acquired immunological tolerance （1960） Sir Frank Macfarlane Burnet ，Australia ，1899-1985 Peter Brian Medawar，UK，1915-1987

II. Types of Immunological tolerance (I) Self –tolerance and induced tolerance Self tolerance: to self antigen Induced tolerance: to foreign antigen (II) Central tolerance and Peripheral tolerance Central tolerance :form in central immune organs Peripheral tolerance : form peripheral immune organs

Self-tolerance Normal individuals are tolerant to their own antigens (self antigen) Tolerance to self antigens is a fundamental property of the normal immune system, the failure of self-tolerance leads to autoimmune disease.

Induced tolerance Foreign antigens may be administered in ways that preferentially inhibit immune response by inducing tolerance in specific lymphocytes Such as Tumor cells can induce immunological tolerance during their proliferation .

Central tolerance induced in central immune organs as a consequence of immature self-reactive lymphocytes recognizing antigens

Peripheral tolerance induced in peripheral immune organs as a result of mature self-reactive lymphocytes encountering self antigens under particular conditions

Section II The conditions of immunological tolerance formation Antigen-associate factors Host–associated factors

I. Antigen-associate factors Types of antigen does of antigens Features of determinant Pathway of antigen entering body

Factors which affect response 1. Types of antigen Factors which affect response Favor immune response Favor tolerance Physical form of antigen Large, aggregated, complex molecules, properly processed soluble, aggregate-free, simple small molecules, not processed

2. does of antigens High-zone tolerance T, B cell tolerance Low-zone tolerance T, B cell tolerance T cell tolerance Immune response

Comparison of T cell tolerance with B cell tolerance ________________________________________________ Contents T cell B cell __________________________________________________________ Tolerance formation easy difficult Antigens TD -Ag TD- Ag and TI –Ag Dose of antigens high or low high Induced time shorter (1-2 days) longer (more than 10 days) Maintaining time longer (a few months) shorter (a few weeks) ___________________________________________________

3. Features of determinant Determinants recognized by Ts or Treg induce tolerance Determinants recognized by conventional T cells initiate immune response

4.Pathway of antigen entering body Oral Intravenous Intra-peritoneal Intramuscular subcutaneous Immune response tolerance

Factors affecting tolerance role of antigen Factors which affect response Favor immune response Favor tolerance Physical form of antigen Route of injection Dose of antigen Large, aggregated, complex molecules, properly processed Subcutaneous or intramuscular Optimal dose soluble, aggregate-free, simple small molecules, not processed Oral or, sometimes, intravenous Very large or very small dose Tolerance to soluble antigens: A state of tolerance to a variety of T-dependent and T-independent antigens has been achieved in various experimental models. Based on these observations it is clear that a number of factors determine whether an antigen will stimulate an immune response or tolerance (Table 1).

II. Host–associated factors Species: easy in murine and rat difficult in human Status of host immune system:

Factors affecting tolerance the role of host Factors that affect response Favor immune response Favor tolerance Age of responding animal Differentiation state of cells Fully differentiated; memory T & B cells Older, immuno-logically mature Newborn (mice), immuno-logically immature Relative undifferentiated B cell with only IgM, T cells in the thymic cortex

Host age and antigen dose affect tolerance newborn adult

Section Ⅲ Mechanism of Immunologic Tolerance

.Central tolerance: Central tolerance occurs in the central lymphoid organs as a consequence of immature self-reactive lymphocytes recognizing ubiquitous self-antigen.----negative selection .Peripheral tolerance: tolerance was induced in peripheral organs as a result of mature self-reactive lymphocytes encountering tissue-specific self antigens under particular conditions

I. Central tolerance T cell central tolerance : formation in thymus clonal deletion in negative selection B cell central tolerance: formation in bone marrow clonal deletion clonal anergy

Clonal deletion: negative selection of T cells in the thymus Clonal deletion: Functionally immature cells of a clone encountering antigen undergo a programmed cell death. For example, auto-reactive T-cell are eliminated in the thymus following interaction with self antigen during their differentiation (negative selection). Clonal deletion has been shown to occur also in the periphery. B cells expressing only IgM (no IgD) on their surface when exposed to antigen are eliminated.

1. T cell central tolerance T cell Clonal deletion (apoptotic cell death) During maturation of T lymphocytes in the thymus, immature T lymphocytes that recognize ubiquitous self-antigen with high affinity are deleted by mechanism of apoptosis

2. B cell central tolerance Clonal deletion During maturation of B lymphocytes in bone marrow , immature lymphocytes that recognize membrane-bound self-antigen with high affinity are deleted by apoptosis Clonal anergy During maturation of B lymphocytes in bone marrow , immature lymphocytes that recognize soluble self-antigen are not deleted but are inactivated

Negative selection of B cells in bone marrow Clonal deletion: Functionally immature cells of a clone encountering antigen undergo a programmed cell death. For example, auto-reactive T-cell are eliminated in the thymus following interaction with self antigen during their differentiation (negative selection). Clonal deletion has been shown to occur also in the periphery. B cells expressing only IgM (no IgD) on their surface when exposed to antigen are eliminated.

Clonal anergy in B cells Also, B cells when exposed to large amounts of soluble antigen down regulate their surface IgM and become anergic and short lived. These cells also up regulate Fas molecules on their surface. An interaction of these B cells with Fas-ligand bearing cells result in their death via apoptosis.

II. Peripheral tolerance T cell Peripheral tolerance Clonal anergy Immunological ignorance Regulatory T cells Activation induced cell death, AICD Immunity privilege B cell Peripheral tolerance Clonal deletion Receptor editing

I) T cell Peripheral tolerance Clonal anergy: An experimentally induced state of antigen unresponsiveness of a clone of T lymphocytes induced by recognition of antigen in the absence of additional signals ( costimulatory signal) T cells survive but are rendered incapable of responding to the antigen even if it is later presented by competent APCs viable and unfunctional

Absence of costimulatory signal If CD4+ T cells recognize peptide antigens presented by APCs that are deficient in costimulators , the T cells survive but are rendered incapable of responding to the antigen even if it is later presented by competent APCs Inhibition of costimulatory signal Anergy may be induced if T cells use the Inhibitory receptor for B7 molecules, CTLA4, to recognize costimulators on APCs at the time that the cells are recognizing antigen

I) T cell Peripheral tolerance 2.Immunologic ignorance A form of lymphocyte unresponsiveness in which self antigens are ignored by the immune system even though lymphocytes specific for those antigens remain viable and functional.

Clonal ignorance Clonal anergy

I) T cell Peripheral tolerance 3.Regulatory T cells A population of T cells that inhibit the activation proliferation of other T cells and may be necessary to the maintaining of peripheral tolerance to self antigens

Regulatory T cells Regulatory CD4+T cells: CD4+CD25+ T cells Regulatory CD8+ T cells: CD8+CD28-T cells Qa-1- restricted CD8+ NK T cells Double negative regulatory T cell: CD3+CD4-CD8-

Induced Treg

CD4+CD25+Tregs In vitro 5-10% of CD4+ T cells FACS Microscopy Co-culture 40 30 20 10 3H uptake (x10-3) CD25– CD25+ + 10% >90% Foxp3 CD25 CD25 Foxp3 CD4 CD25 In vivo Maintain immune tolerance Inhibit autoimmunity prevent transplant rejection Interfere with anti-cancer immunity Potential in immune deficiency In vitro 5-10% of CD4+ T cells Anergic to TCR stimulation Suppress T cell proliferation

I) T cell Peripheral tolerance 4. Activation-induced cell death (AICD) Repeated stimulation of T lymphocytes by persistent antigens results in death of the activated cells by a process of apoptosis

I) T cell Peripheral tolerance 5. Immunologically privileged sites anatomic barrier Action of Suppressor lymphocyte (Ts) Action of cytokines: TGF- , IL-10

II) B cell Peripheral tolerance Clonal deletion :AICD Lack of Th cell help : Th cell anergy Clonal anergy : express insensitive mIg lack costimulatory molecules Receptor editing : from self-reactive B cell clone to foreign antigen-reactive B cell lone

Clonal anergy

I. The significance of theoretical research Section I V Significance and clinical application of immunologic Tolerance I. The significance of theoretical research II. The significance and application on clinical therapy

I. The significance of theoretical research Immunologic tolerance is very important for maintaining homeostasis Homeostasis: The maintaining of constant number of cells called homeostasis Immune response to foreign antigens are eliminated, returning the immune system to its basal resting state. Deletion ( AICD), Immunologic tolerance is an very important mechanism of immunoregulation

II. The significance and application on clinical therapy

(I) Induce immunologic tolerance to treat autoimmune diseases Block costimulaotry signal CD28/B7 CD40/CD40L CD137/CD137L enhance inhibition of regulatory T cell CD4+CD25+ Treg Oral tolerance ：the oral administration of a protein antigen often leads to a marked suppression of systemic humoral and cell-mediated immune response to immunization with the same antigen

(II) Induce immunologic tolerance to prevent or treat hypersensitivity

(III) Induce immunologic tolerance to prevent or treat graft rejection Block costimulaotry signal CD28/B7 CD40/CD40L CD137/CD137L enhance inhibition of regulatory T cell CD4+CD25+ Treg Oral tolerance ：the oral administration of a protein antigen often leads to a marked suppression of systemic humoral and cell-mediated immune response to immunization with the same antigen

(IV) Break up tumor immune tolerance to treat tumor Enhance costimulaotry signal CD28/B7 CD40/CD40L CD137/CD137L Deletion of regulatory T cell CD4+CD25+ Treg