免疫耐受和免疫调节

1、Immune tolerance & Immune Regulation Lu,LinrongInstitute of Immunology, ZJULu.L Immune tolerance or Immunological tolerance is the process by which the Immune system does not attack an antigen. It is a kind of specific immunological unresponsiveness to a given antigen.It occurs in 2 forms: Natur

2、al tolerance (self tolerance) Acquired tolerance (induced tolerance).Definition Self tolerance: Individuals normally do not respond to their self“ antigens, i.e., they are tolerant to self. This is the basis for self- non self discrimination by the immune system to ensure immune system not to attack

3、 self. Loss of self tolerance can lead to autoimmunity.Natural Tolerance (self tolerance) Induced unresponsiveness to foreign Ags.It can be used to facilitate transplantation or when tolerance is necessary(acquired tolerance)Acquired toleranceImmune toleranceImmune tolerance is an active process whi

4、ch is different from immunodeficiency or immunosuppression.Immunodeficiency: A disorder or state in which the Immune systems ability to fight infectious disease is compromised or entirely absent. Overall Inability of the immune system to respond to a broad range of antigens. (genetic reason or AIDS)

5、Immunosuppression: A condition where the activation or efficacy of the immune system is reduced (induced by an immunosuppressant ). Early Observations Ray Owen, 1945Dizygotic cattle twins that shared the same placenta were blood cell chimaeras, ie contained blood cells of two different haplotypes in

6、 adults and, - these two haplotypes co-existed in the adults without mutual rejection.Ray OwenSuch chimaeric cattle will exchange skin grafts without rejection. Normally, if cells of one of the two haplotypes were transferred to an adult cattle of the other haplotype, these were promptly rejected. T

7、hus, tolerance in the dizygotic twins resulted from the sharing of the placenta in fetal life.Billingham and Medawars experimentChimeric mice1960 Nobel Prize*Definition *History-Early observations*Mechanism *Induction Immunological ToleranceT cell develop in the thymusPositive selection: During posi

8、tive selection Double-Positive T cells that can recognize self MHCs are selected for proliferation, and those T cells that do not recognize self MHC die via Apoptosis. Positive selection assures TCR to recognize peptide/MHC complex and also go with the appropriate CD4 or CD8. For example, TCRs speci

9、fic for MHC II need to retain CD4, and lose CD8. The same is true for the T cells that are specific for MHC I, which need to retain CD8, and lose CD4.Thymocytes are positive selected by MHC/self peptidesdeath by neglect !Negative selection: T cells that are strongly activated by self MHC plus self p

10、eptides need to be eliminated in the thymus. complex.If they escape this elimination, they may subsequently react against self antigens, and cause Autoimmune disease.Central Tolerance is achieved by negative selectionAvidity Model: Avidity depends on the affinity of the TCR-peptide/MHC interaction a

11、nd the density of the peptide/MHC on the thymic epithelial cell. Avidity determines the strength of signal delivered which dictates the outcome. Stronger signals may mean longer signaling or additional signaling.Positive selection vs Negative selection Affinity/Avidity modelIn summary, Positive sele

12、ction selects for those T cells that react with MHC: self antigen. Negative selection eliminates those that react strongly with MHC: self antigen. Thus, successful T cell differentiation selects for MHC restricted TCRs with low affinity for self antigens. The rationale here is that a T cell that bin

13、ds weakly to self MHC/self Antigen will not be activated but will be activated by a stronger binding to self MHC/ foreign AntigenSummary of central toleranceParadox: Deletion of T cells in the thymus requires local expression of the cognate tissue specific antigens (e.g.insulin, MBP).What cell in th

14、e thymus is expressing self-proteins?What makes this particular cell to express all these tissue-specific genes?Central toleranceThe answer:A large variety of tissue specific proteins are expressed in the thymus by MEC (medullary epithelial cell)But How?Central tolerance Central tolerance AIRE(autoi

15、mmune regulator): transcription factor that enables ectopic expression in the thymus of genes usually considered tissue-specificNormalAIRE knockoutFrom M. Anderson, et al. (Laboratory of C. Benoist and D. Mathis).Joslin Diabetes Center and Harvard Medical School; Science 298:1395, 2002AIRE knockout

16、lead to autoimmune diseases Autoantibodies in AIRE knockout miceDeletion of self-reactive T cells in the thymusAIRE (autoimmune regulator) is a putative transcription factor that stimulates expression of many self antigens in in the thymusDiane Mathis and Christophe BenoistCentral toleranceDiane and

17、 Chris visiting ZJUHumans expressing a defective form of the transcription factor AIRE (autoimmune regulator) develop multiorgan autoimmune disease. Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED)。 APECED, also known as autoimmune polyendocrine syndrome-type 1(APS-1), is a po

18、lyglandular disorder that classically manifests as spontaneous autoimmunity against the parathyroid and/or adrenal glands, and/or by a mucocutaneous candidiasis infection. Other common ailments include autoimmune forms of premature ovarian failure, hepatitis, anemia, diabetes, alopecia, and vitiligo

19、. It seemed reasonable to hypothesize that APECED patients develop multiorgan autoimmunity because a defect in AIRE prevents or modifies ectopic transcription of genes encoding peripheral tissue-restricted antigens in thymic MECs. APECED in human AIRE Structure and MutationsPeripheral tolerance (Imm

20、une Regulation)Why we need a peripheral tolerance ?Some antigens are not expressed in thymus or bone marrow, which leads to the possibility to trigger immune response.Negative selection is incomplete: Middle to low affinity self-reactive clones are released to peripheral and can be activated under c

21、ertain conditions.APCTCRCD28 APCTCRFunctionalunresponsivenessNormal T cellresponseAnergy Apoptosis (activation-induced cell death)APCDeletion APC Block inactivationSuppression RegulatoryT cellPeripheral T cell toleranceOff signalsAnergy induced without co-stimulation*Most tissue cells dont express c

22、o-stimulation receptors*Professional APCs dont express co-stimulation receptors without activationPeripheral T cell toleranceActivation-induced Cell Death(AICD)* Persistent presence of self-antigen gives repeated stimulationPeripheral T cell toleranceActivation-induced Cell Death(AICD)Defect in Fas

23、or FasL triggers AutoimmunityFasNormalFas LAutoimmunity and lymphoproliferative diseaseFas LFas+Fas-ALPS Patient: An unusual mutationHealthy female - at 18 months developed cervical adenopathy(颈淋巴结肿大). Biopsy showed reactive hyperplasiaDeveloped anemia with hypersplenism, hematuria, proteinuria and

24、renal insufficiency due to mesangial glomerulonephritis, then primary biliary infiltration. Evaluation at NIH: lymphadenopathy persists, ANA (+) 1:320, CD4-CD8- cells 25% of ab T cells, increased B cells; Fas surface expression is normal.Heterozygous Fas splice mutation resulting in loss of exons 3,

25、 4 (AA 52-96)WT Fas PT 228 66 128 174 214 298 51 97del 52-96TMTMImmunoregulation by TregsCD4+FoxP3+ TregsCD8+ TregsOther regulatory cellsNatural Treg: constitute approximately 10% of CD4+ T cells in spleen and lymph nodes of normal mice, 1030% of CD4+T cells in peripheral blood of human. Naturally a

26、nergic and suppressive, appear to be produced by the normal thymus as a functionally distinct subpopulation of T cells. 2) Surface markers CD25 (IL-2R), IL-2R, CTLA-4, GITR, CD44high, CD45RB, CD5high, ICAM-1high, LFA-1high, partly CD62L. The expression pattern of some accessory molecules is in part

27、similar to primed , activated, effector, or memory T cells.3) Inducible Treg（iTreg）- that differ in terms of their development, specificity, mechanism of action and dependence on T-cell receptor and co-stimulatory signaling.CD4+FoxP3+ TregsFoxP3 is the transcription factor that program the developme

28、nt of TregsAlexander Y. RudenskyUniversity of WashingtonShimon SakaguchiKyoto University，RIKENCD4+FoxP3+ TregsNature Immunol 4:330-336.IPEX Immune deficiency/dysregulation Polyendocrinopathy Enteropathy (Often have Ab against gut epithelium) X-linked inheritancePatients have mutations in FOXP3 gene.

29、 They suffer from inflammatory diseases similar to that seen in mice deficient in CD4+CD25+ Treg cells.IPEX (Clinical Findings) First described in 1982 by Powell et al. as a syndrome of diarrhea, polyendocrinopathy, and fatal infection in infancy. Neonatal onset diabetes mellitus(新生儿糖尿新生儿糖尿病病) Hypot

30、hyroidism (甲状腺功能减退甲状腺功能减退) Enteritis (diarrhea/villous atrophy)(肠炎肠炎) Hemolytic anemia & thrombocytopenia. Dermatitis Dermatitis (eczema，湿疹，湿疹) Death by 1-2 years of ageCD25FOXP3IPEX NormalIPEX DiagnosisPROLINE-RICH DOMAINZINC-FINGER LEUCINEZIPPERFORKHEAD DOMAINNCNLSFOXP-3 is the master control

31、gene for Treg development, encodes a novel forkhead/winged helix transcription factorFOXP3 Mutations Zn - finger FKH (DNA binding)Zip ATGA38SC424YR397WR397WR397LdelGA(TGA)1317-1318delT(TGA)13115-1316I363VF371CAgG+4AgGA384TA384T A384TA384TR347Pdel251EC565T splicingC565T splicingL76frameshift1 2 3 4 5

32、 6 7 8 9 10 11 PolyA Regulation by Inhibitory receptors1. Immune cells are activated by Ligand binding to their activating receptors2. Activation of Immune cells is mediated by Protein Phosphorylation:3. Phosphorylation is mediated by protein kinases; Dephosporylation is catalyzed by protein phospho

33、tases.1). Activating receptor: ITAM (immunoreceptor tyrosine-based activation motif) Motifs：YxxL/V Recruit : kinases, adaptor proteinsInduce activation signal2). Inhibitory receptor:ITIM (immunoreceptor tyrosine-based inhibitory motif) Motifs：I/Vx YxxLRecruit Protein phosphatasesTransduce inhibitory

34、 singnalRegulation by Inhibitory receptorsTwo type of receptorsCell typeActivation Triggeractivation motifKinase recruitedB cellBCR ITAM (Ig Ig)LynT cell TCR ITAM (CD3)LckNK cellNKG2D ITAM （DAP12）Syk.Activating receptors mediate cellular activationRegulation by Inhibitory receptorsRegulation by Inhi

35、bitory receptorsInhibitory receptorsOnce the ITIM of FcRIIB is phosphorylated, SH2-containing SHIP are recruited, which influences PI3K and ERKpathways. PIRB（paired immunoglobulin-like receptor B ） ITIMs recruites SHP1，which dephosphorylates various protein-tyrosine kinases, including SYK and Bruton

36、s tyrosine kinase (BTK). Inhibitory receptors on B cellInhibitory receptors for T cell. CTLA-4Y201 YVKMY208Inhibitory receptorsDynamic regulations of T cell activation by CD28 and CTLA4: CD28 and CTLA-4 has the same ligand B7. Resting T cell only express CD28, which is an activating coreceptor provides 2nd signaling to ensure T cell activation.Activated T cells start to express CTLA-4 on their surface, because CTLA-4 has 100 folder higher affinity to B7, CTLA-4 activation become dominant wh