1. Chapter 10 Immunologic Tolerance
General Features and Mechanisms
T Lymphocyte Tolerance
B Lymphocyte Tolerance
Tolerance induced by Foreign Protein Antigens
Homeostasis in the Immune System

2. What is Immunologic Tolerance?
Immunologic Tolerance—— an antigen induced specific unresponsiveness
Tolerogens  Immunogens
Self-tolerance  Autoimmunity
Tolerance induced by foreign antigens
Failure
Introduction:
Tolerance refers to the specific immunological non-reactivity to an antigen resulting from a previous exposure to the same antigen. While the most important form of tolerance is non-reactivity to self antigens, it is possible to induce tolerance to non-self antigens. When an antigen induces tolerance, it is termed tolerogen.

3. General Features and Mechanisms
Immunologically specific
A result of antigen recognition by specific lymphocytes

4. _ + + Studies of graft rejection in inbred mice
Strain A
Strain A
Strain A
Neonate
Adult _
Skin graft rejection + +
移植以另一品系小鼠的骨髓，至小鼠长至6周，再移植以该骨髓来源品系小鼠的皮肤
During lymphocyte maturation in the generative lymphoid organs, all lymphocytes pass through a stage in which encounter with Ag leads to tolerance
Immunologically specific
a result of the recognition of antigens by specific lymphocytes

5. General Features and Mechanisms
Immunologically specific
Central tolerance: induced in generative lymphoid organs immature self-reactive lymphocyte
The repertoire of mature lymphocytes cannot recognize ubiquitous or widely disseminated self antigens
The repertoire of mature lymphocytes cannot recognize ubiquitous or widely disseminated self antigens

6. Burnet: Clonal selection hypothesis

7. General Features and Mechanisms
Immunologically specific
Central tolerance: generative lymphoid organs immature self-reactive lymphocyte
Peripheral tolerance: peripheral sites mature self-reactive lymphocytes
The repertoire of mature lymphocytes cannot recognize ubiquitous or widely disseminated self antigens
The repertoire of mature lymphocytes cannot recognize ubiquitous or widely disseminated self antigens
Important for maitaining unresponsiveness to self antigens that are not expressed in the generative lymphoid organs.

8. Peripheral tolerance is induced when mature lymphocytes recognize antigens without adequate levels of the costimulators.

9. The principal mechanisms of lymphocyte tolerance
Central tolerance
Deletion: apoptotic cell death
Anergy: functional inactivation without cell death
Treg
Peripheral tolerance

10. Apoptosis
Apoptosis. Light micrographs of (a) normal thymocytes (developing T cells in the thymus) and (b) apoptotic thymocytes. Scanning electron micrographs of (c) normal and (d) apoptotic thymocytes. [From B. A. Osborne and S. Smith, 1997, Journal of NIH Research 9:35; courtesy B. A. Osborne, University of Massachusetts
at Amherst.]

11. Immunologic Tolerance
General Features and Mechanisms
T Lymphocyte Tolerance
B Lymphocyte Tolerance
Tolerance induced by Foreign Protein Antigens
Homeostasis in the Immune System

12. T Lymphocyte Tolerance
Central T Cell Tolerance
Peripheral T cell Tolerance

13. Maturation of T cells in the thymus
Diagrammatic cross section of a portion of the thymus,
showing several lobules separated by connective tissue strands
(trabeculae). The densely populated outer cortex is thought to contain
many immature thymocytes (blue), which undergo rapid proliferation
coupled with an enormous rate of cell death. Also present in
the outer cortex are thymic nurse cells (gray), which are specialized
epithelial cells with long membrane extensions that surround as
many as 50 thymocytes. The medulla [me”dʌlə] is sparsely populated and is
thought to contain thymocytes that are more mature. During their
stay within the thymus, thymocytes interact with various stromal
cells, including cortical epithelial cells (light red), medullary epithelial
cells (tan), interdigitating dendritic cells (purple), and macrophages
(yellow). These cells produce thymic hormones and express high levels
of class I and class II MHC molecules. Hassalls corpuscles,
found in the medulla, contain concentric layers of degenerating epithelial
cells. [Adapted, with permission, from W. van Ewijk, 1991,

14. Negative selection: Development of central tolerance
In immature t cells, the consequence of high avidity antigen recognition is the triggering of apoptosis, leading to death or deletion of the cells
High affinity
High concentration

15. Self antigens expressed in the thymus
ubiquitous self-antigen: widely expressed in the body
tissue-specific antigen autoimmune regulator gene, AIRE

16. Natural Tregs arise in the thymus
Natural Tregs arise in the thymus as thymocytes interact with mTEC expressing tissue-specific antigens driven by the transcription factor AIRE. An increased affinity interaction between the pMHC complex and the TCR along with the secondary signals stimulates developing thymocytes to express Foxp3 and activates a gene expression profile driving natural Treg development
天然调节T细胞在维持自身耐受中其主要作用

17. 天然调节T细胞在维持自身耐受中其主要作用

18. T Lymphocyte Tolerance
Central T Cell Tolerance
Peripheral T cell Tolerance

19. Peripheral T cell Tolerance
Antigen recognition without adequate costimulation
Use CTLA-4 to recognize costimulators on APCs
Activation induced cell death (AICD)
Regulatory T Lymphocytes
Factors that determine the tolerogenicity of self antigens

20. Peripheral T cell Tolerance
Antigen recognition without adequate costimulation
Use CTLA-4 to recognize costimulators on APCs
AICD
Treg
Factors that determine the tolerogenicity of self antigens

21. Two Signal model Sig2 (co-stimulation) 1975 Lafferty & Cunningham
T helper cells die when they see antigen unless rescued by co-stimulation(signal two) from APCs. 21

22. co-stimulatory signal
For a T cell to be activated by a specific antigen, the T cell receptor must recognize complexes of MHCI with the antigen on the surface of an antigen-presenting cell. T cells and the T cell receptor complex do not respond to antigen in solution, but even for the specific antigen they only respond to antigen-MHC-1 complexes on the cell surface. This interaction is necessary for T cell activation, but it is not sufficient. T cell activation also requires a co-stimulatory signal involving interaction of CD28 on the T cell with CD80 or CD86 (B7 family genes) on the antigen-presenting cell. CD28 activates a signal transduction pathway acting through PI-3K, Lck and Grb-2/ITK to provide its co-stimulatory signal for T cell activation. Another means to control T cell activation is by expressing factors that down-regulate T cell activation. Signaling by activated T cell receptors induces expression of CTLA-4, a receptor that opposes T cell activation. CTLA-4 has a higher affinity than CD28 for B7 proteins, terminating T cell activation. ICOS is a protein related to CD28 that is only expressed on activated T cells, and that provides another important co-stimulatory signal. The requirement for co-stimulatory signals provides additional control mechanisms that prevent inappropriate and hazardous T cell activation 22

23. Figure 8-20
Gowth factor: IL-2

24. Anergy is induced when mature lymphocytes recognize antigens without adequate levels of the costimulators.

25. Peripheral T cell Tolerance
Antigen recognition without adequate costimulation
Use CTLA-4 to recognize costimulators on APCs
AICD
Treg
Factors that determine the tolerogenicity of self antigens

26. Figure 8-12
CTLA-4/B7 initiate the inhibitory signal

27. Anergy may be induced if T cells use CTLA-4 to recognize costimulators on APCs

28. Question
Factors ? ?
T cells
T cells
T cells
recognize B7 molecules with CD28 (active receptor) ? ? ? ? ? ?
Recognize the same B7 with CTLA-4 (inhibitory receptor)
Immune response
Raise the questions
Tolerance

29. Making and breaking tolerance
感染致树突状细胞成熟和活化
The nature of tissue APCs is an important determinant of whether self-tolerance or autoimmunity develops.

30. Peripheral T cell Tolerance
Antigen recognition without adequate costimulation
Use CTLA-4 to recognize costimulators on APCs
AICD
Treg
Factors that determine the tolerogenicity of self antigens

31. Activation induced cell death
Repeated stimulation of T cells by persistent antigen results in death of the activated cells by a process of apoptosis

32. Fas-mediated activation-induced cell death
AICD is a form of apoptosis induced by signals from membrane death receptors

33. activation
activation
The net effect is that the population of mature lymphocytes is depleted of antigen specific lymphocytes by repeated stimulation.

34. Peripheral T cell Tolerance
Antigen recognition without adequate costimulation
Use CTLA-4 to recognize costimulators on APCs
AICD
Regulatory T Lymphocytes (Treg)
Factors that determine the tolerogenicity of self antigens

35. Treg cell development
Immunity 2009; 30: p626

36. T cell-mediated suppression

37. Mechanisms of action of regulatory T cells
Figure 1 | Two classes of regulatory T cells can be envisioned. a | In this hypothetical model, the natural regulatory T (TReg) cells (blue) suppress immune responses in a contact-dependent manner and function in general homeostasis to block the actions of autoimmune T cells (red) in non-inflammatory settings. b | The adaptive TReg-cell subset enhances the robust nature of suppression in an inflammatory milieu. Importantly, adaptive TReg cells can develop either from CD4+CD25+ natural TReg cells (blue striped) or by altering the activity of T helper (TH) cells (red striped). APC, antigen-presenting cell; IL-10, interleukin-10; TGF-β, transforming growth factor-β.
Physiological roles of TReg-cell subsets
The two TReg-cell subsets might function in different immunological settings, depending on the context of antigen exposure, the nature of the inflammatory response and the TCR repertoires of the individual cells. We argue that natural TReg cells would be most effective at suppressing autoreactive T-cell responses locally, in non-inflammatory settings circumstances in which antigen-specific, self limiting reactions are required to achieve a fine homeostatic balance. By contrast, during self-damaging inflammatory reactions to microbes or transplanted tissue, or in settings of inflammatory autoimmune disease that are more similar to the infectious setting (for example, inflammatory bowel disease), adaptive TReg cells might be induced to suppress the pathological immune responses. Although this functional activity might also require cell–cell contact, the resulting suppression is amplified by the secretion of inhibitory cytokines.

38. Peripheral T cell Tolerance
Antigen recognition without adequate costimulation
Use CTLA-4 to recognize costimulators on APCs
AICD
Regulatory T Lymphocytes (Treg)
Factors that determine the tolerogenicity of self antigens

39. Factors That Determine the Immunogenicity and Tolerogenicity of Protein
Factors that favor stimulation of immune response
Factors that favor tolerance
Amount
Optimal doses that vary for different antigens
High doses
Persistence
Short-lived (eliminated by immune response)
Prolonged (AICD)
Portal of entry; location
Subcutaneous, intradermal; absence from generative organs
Intravenous, oral; presence in generative organs
Presence of adjuvants
Antigens with adjuvants: stimulate helper T cells
Antigens without adjuvants:
Properties of APCs
High levels of costimulators
Low levels of costimulators and cytokines

40. Immunologic Tolerance
General Features and Mechanisms
T Lymphocyte Tolerance
B Lymphocyte Tolerance
Tolerance induced by Foreign Protein Antigens
Homeostasis in the Immune System

41. B Lymphocyte Tolerance
Central B Cell Tolerance
Peripheral B cell Tolerance
Checkpoints during B cell maturation and activation at which encounter self Ags may abort these process

42. B cell development in bone marrow
The maturation of B and T lymphocytes consists of sequential stages-lineage commitment and proliferation, expression of antigen receptor genes, and selection of mature repertoires. The earliest bone marrow cells committed to the B cell lineage is called a pro-B cell. The pre-B cell represents the next stage of development

43. 淋巴样干细胞、未接触抗原的B细胞、受抗原驱动成为记忆细胞或浆细胞

44. Central tolerance in B cells
Immature B cells that recognize self antigens in the bone marrow with high affinity are deleted or change their specificity.
multivalent self antigens: cell membrane molecules、polymeric molecules

46. Down-regulation of antigen receptor expression
What is the result of self antigen recognition in generative lymphoid organ?
HEL transgenic
Down-regulation of antigen receptor expression
Change in receptor specificity (receptor editing)

47. B Lymphocyte Tolerance
Central B Cell Tolerance
Peripheral B cell Tolerance

49. B7
CD28
T-B Collaboration

51. Peripheral tolerance in B cells
Mature B cells that recognize self antigens in peripheral tissues in the absence of specific helper T cells may be rendered functionally unresponsive.
If anergic B cells do encounter any antigen-specific helper T cells, what happened?
The B cells maybe killed by FasL on the T cells engaging Fas on the B cells.

52. systemic lupus erythematosus
脑 Brain 癫痫 seizures 精神病 psychosis 头痛 headache
头发 Hair 脱发 alopecia
脸 Face 颊部红斑 malar rash 盘状红斑 discoid rash
肺 Lungs 胸膜炎 pleurisy 间质性肺炎 interstitial pneumonia
心 Heart 心包炎 pericarditis 心肌炎 myocarditis 心内膜炎 endocarditis 肺动脉高压 pulmonary hypertension
血液、血管 Blood & Vessels 血管葱皮样改变 onion-skin like artery 贫血 anemia 血栓 thrombosis
小肠 Intestines 血管炎 vasculitis
手 Hands 雷诺氏现象 Raynauds phenomenon Jaccoud关节病
肾 Kidneys 蛋白尿 proteinuria 管型 casts
关节 Joints 关节炎 arthritis
足 Feet 血管炎 vasculitis
systemic lupus erythematosus 

53. 蝶型红斑 （Butterfly rash）

54. Homogenous pattern
Peripheral pattern
Speckled pattern

55. Normal individals do not produce autoantibodies against self protein antigens, and this may be due to deletion or tolerance of helper T lymphocytes even if functional B cells are present.
Defects in the maintenance of T cell tolerance may result in autoantibody production

56. Thymus (cortex); peripheral Bone marrow; peripheral
Feature
T lymphocyte
B lymphocyte
Principal sites
Thymus (cortex); peripheral
Bone marrow; peripheral
Tolerance-sensitive stage
CD4+CD8+ thymocyte
Immature B lymphocytes
Stimuli for tolerance induction
Central: high-avidity recognition of Ag in thymus
Central: high-avidity recognition of multivalent Ag in bone marrow
Peripheral: Ag presentation by APCs lacking costimulators; repeated stimulation by self Ag
Peripheral: Ag recognition without T cell helper
Principal mechanisms of tolerance
Central tolerance: clonal deletion (apoptosis)
Central tolerance: clonal deletion (apoptosis), receptor editing
Peripheral tolerance: anergy, AICD, suppression
Peripheral tolerance: block in signal transduction (anergy); failure to enter FC

57. Immunologic Tolerance
General Features and Mechanisms
T Lymphocyte Tolerance
B Lymphocyte Tolerance
Tolerance induced by Foreign Protein Antigens
Homeostasis in the Immune System

58. Factors That Determine the Immunogenicity and Tolerogenicity of Protein
Factors that favor stimulation of immune response
Factors that favor tolerance
Amount
Optimal doses that vary for different antigens
High doses
Persistence
Short-lived (eliminated by immune response)
Prolonged (AICD)
Portal of entry; location
Subcutaneous, intradermal; absence from generative organs
Intravenous, oral; presence in generative organs
Presence of adjuvants
Antigens with adjuvants: stimulate helper T cells
Antigens without adjuvants:
Properties of APCs
High levels of costimulators
Low levels of costimulators and cytokines

59. Immunologic Tolerance
General Features and Mechanisms
T Lymphocyte Tolerance
B Lymphocyte Tolerance
Tolerance induced by Foreign Protein Antigens
Homeostasis in the Immune System Termination of normal immune response

60. Mechanisms of the decline of normal immune response (homeostasis)
CTLA-4、Fas、FasL

61. T cell B7 CD28 Ag TCR CTLA-4 Active signal I T I M I TAM
24 h B7
CD28 Ag
TCR
CTLA-4
Active signal
I T I M
I TAM
Inhibitory signal
T cell

62. Antibody feedback

63. The repertoire for TCR and BCR (Ab)
Niels Jerne: Network hypothesis
Ab1
Ab2 Ag
Ab3
threshold
阈值之下的各种显示独特型的淋巴细胞，就是由数量极大的感知元件组成的一种洞察抗原刺激并具有引发特异性应答潜在能力的网络。
The repertoire for TCR and BCR (Ab)
Idiotype and anti-idiotypic
Reach a steady state at which the immune system is at homeostasis

64. Summary What is immunologic tolerance?
Central and peripheral tolerance
Tolerance in T and B cells
Homeostasis

65. What is Immunologic Tolerance?
Tolerance—— an antigen induced specific unresponsiveness
Tolerogens  Immunogens
Self-tolerance  Autoimmunity
Tolerance induced by foreign antigens
Introduction:
Tolerance refers to the specific immunological non-reactivity to an antigen resulting from a previous exposure to the same antigen. While the most important form of tolerance is non-reactivity to self antigens, it is possible to induce tolerance to non-self antigens. When an antigen induces tolerance, it is termed tolerogen.

66. Thymus (cortex); peripheral Bone marrow; peripheral
Feature
T lymphocyte
B lymphocyte
Principal sites
Thymus (cortex); peripheral
Bone marrow; peripheral
Tolerance-sensitive stage
CD4+CD8+ thymocyte
Immature B lymphocytes
Stimuli for tolerance induction
Central: high-avidity recognition of Ag in thymus
Central: high-avidity recognition of multivalent Ag in bone marrow
Peripheral: Ag presentation by APCs lacking costimulators; repeated stimulation by self Ag
Peripheral: Ag recognition without T cell helper
Principal mechanisms of tolerance
Central tolerance: clonal deletion (apoptosis)
Central tolerance: clonal deletion (apoptosis), receptor editing
Peripheral tolerance: anergy, AICD, suppression
Peripheral tolerance: block in signal transduction (anergy); failure to enter FC

67. THANK YOU

68. Innate and adaptive Immunity
Naïve lymphocytes
Mature lymphocytes that have not previously encountered antigen; function -- antigen recognition
Preferential migration to peripheral lymphoid organs (lymph nodes), the sites where immune responses start
Effector lymphocytes
Activated lymphocytes capable of performing the functions required to eliminate microbes (‘effector functions”)
Effector T lymphocytes: cytokine secretion (helper cells), killing of infected cells (CTLs)
B lymphocytes: antibody-secreting cells (e.g. plasma cells)