Chapter 10 T-Cell Maturation, Activation, and Differentiation

1. Chapter 10 T-Cell Maturation, Activation, and Differentiation MHC CD4/CD8 TCR zz gde Dec 7 & 12, 2006

2. 你需要學習的課題： 1. 什麼叫做 positive selection 及 negative selection？ 它們產生什麼結果？ 2. T 細胞需要 costimulatory signals 才得完全活化。 3. 什麼叫做 clonal anergy？ 4. Superantigen 有何性質及作用？ 5. T 細胞分化及其 subpopulations。 6. T 細胞凋亡。

3. Two-step Selection Process of Thymocytes Positive Selection: permits the survival of only those T cells whose TCRs recognize self-MHC molecules.  generation of aself-MHC-restricted repertoire of T cells Negative Selection: eliminates T cells that react too strongly with self-MHC or with self-MHC plus self-peptides.  generation of a T-cell repertoire that isself-tolerant Thymic stromal cells, which express high levels ofclass Iandclass II MHC molecules, play a role in this process.

4. ThymicStromal CellsPlay Essential Roles in Positive and Negative Selection Stromal cells: (expressing Notch ligand) produce regulatory factors and express high levels of class I and class II MHC molecules maturation

5. Development of ab T Cells in the Mouse receptor for stem-cell growth factor adhesion molecule involved in homing [CD3-, CD4-, CD8-] recombination-activating gene (RAG-1/2) a chain of IL-2R (double negative; CD4-CD8-) H L < 5% positive selection negative selection

6. Pre-TCR (pre-Ta / TCRb) Activates Signal Transduction Pathways

7. Thymic Selection of the T-Cell Repertoire

8. PositiveSelection Ensures MHC Restriction (double positive cells) class I class II death by neglect !

9. NegativeSelection Ensures Self-tolerance

10. Thymus only selects for T cells whose TCRs recognize Ag presented on target cells with the haplotype of the thymus irradiated infect withLCMV chimeric mouse (source for cytotoxic T cells)

11. Positive Selection Requires Binding of Thymocytes to Class I or Class II MHC Molecules

12. CD8+ T cells only mature in transgenics with H-2k corresponding to the MHC restriction of the TCR transgene → Interaction between TCR and self-MHC on immature thymocytes is required for positive selection.

13. Negative Selection of Thymocytes Requires Both Self-peptide & Self-MHC → Interaction between TCR and MHC + peptide on immature thymocytes is required for negative selection. → H-Y-reactive thymocytes were self-reactive in the male mice and were eliminated. ♂ ♀

14. A Paradox in Positive and Negative Selection The T cells which recognize self-MHC : after positive selection → survival ↓ after negative selection → death What is left???

15. Study of Thymic Selection in Vitro consisting of CD4-CD8- thymocytes gestational age of day 16 ↓ Study the development of T cells in vitro

16. Effect of Peptides in Thymic Selection • TAP deficient cells (described in Chapter 8 p. 211) • RMA-S cell line is an antigen processing-defective tumor cell line. It • expresses only ~ 5% of the normal levels of class I MHC on the membrane, • although the cells synthesize normal levels of class I a chains and b2M. • Addition of pre-digested peptides to RMA-S cells restores the expression • of class I MHC molecules on the membrane. TAP -/- mouse very few CD8+ cells When a diverse peptide mixture is added to the culture, the CD8+ T-cell restoration is greater than when a single peptide is added.

17. dependent on TCR-peptide-class I interactions recognizes a specific MHC- LCMV peptide unable to form peptide-MHC complexes unless peptide is added avidity hypothesis (quantitative) vs differential-signaling hypothesis (qualitative)

18. Models for the Role of CD4/CD8 Coreceptors in DP → SP (double positive to single positive) T Cells

20. TH -Cell Activation The central event in the generation of both humoral and cell-mediated immune responses is the activation and clonal expansion ofTH cells. Interaction of a TH cell with Ag initiates a cascade of biochemical events that induces the resting TH cell to enter the cell cycle, proliferating and differentiatingintoeffectorcells ormemorycells.

21. TCR Engagement Initiates Multiple Signaling Pathways Overview of Common Themes in Signal Transduction (Chapter 1 p.11) (hydrophobic)

24. MultipleSignaling Pathways Are Initiated by TCR Engagement ITAM: immunoreceptor tyrosine-based activation motif

27. Activation of the small G protein, Ras

28. Immediate genes, expressed within 30 min of Ag recognition, encode a number of transcription factors.

29. Early genes, expressed within 1 – 2 hr of Ag recognition, encode cytokines & cytokine receptors.

30. Late genes, expressed more than 2 days after Ag recognition, encode various adhesion molecules.

31. Co-stimulatory Signals Are Required for Full T-cell Activation Naïve T cells require 2 distinct signals for activation and proliferation into effector cells Signal 1 the initial signal, is generated by interaction of an antigenic peptide with the TCR-CD3 complex. Signal 2a subsequent Ag-nonspecific co- stimulatory signal, is provided by interactions betweenCD28on the T cell and members of theB7family on the APC.

32. TH-cell Activation Requires a Co-stimulatory Signal Provided by APCs CD28 is expressed by both resting and activated T cells. + - B7-1 (CD80) B7 (B7-1 and B7-2) are constitutively expressed on dendritic cells, and induced on activated macrophages and activated B cells. B7-2 (CD86) (CD152) CTLA-4 is expressed on activated T cells. CD28 & CTLA-4 act antagonistically.

33. Clonal Anergy Ensues if a Co-stimulatory Signal Is Absent Clonal Anergy (Unresponsiveness): - inability of cells to proliferate in response to a peptide-MHC complex - If a resting TH cell receives the TCR-mediated signal (signal 1) in the absence of a suitable co-stimulatory signal (signal 2), the TH cell become anergic. - In the presence of both signal 1 and signal 2,clonal expansionresults.

34. induction of B7 is inhibited. CD28 no signal 2 no signal 2

35. The Resulting Anergic T Cells Cannot Respond to Normal APCs

36. signal 1 signal 2 signal 1 signal 2

37. Differences in the Properties of 3 Kinds of Professional APCs

38. Activation of a TH Cell Up-regulates Expression of IL-2 and IL-2 Receptor, Leading to the Entry of the T Cell into the Cell Cycle The co-stimulatory signal increases the half-life of the IL-2 mRNA ↓ IL-2 100 x ↑ entry into cell cycle effector T → TH & T C memory cells

39. EffectorTH cells: short-lived TH1 subset:- secretes IL-2, IFN-g, and TNF-b - responsible for cell-mediated functions, such as delayed-type hypersensitivity and the activation of CTL TH2 subset:- secretes IL-4, IL-5, IL-6, and IL-10 - helper for B-cell activation MemoryTH cells: long-lived - Less stringent requirements for activation due to the expression of high levels of numerous adhesion molecules RegulatoryT cells (Treg): CD4+CD25+ cells that inhibit the proliferation of other T-cell populations in vitro.

40. Superantigen-mediated Crosslinkage of TCR and Class II MHC Molecules Exogenous superantigens : exotoxins secreted by G(+) bacteria, e.g., staphylococcal enterotoxin A & B (SEA, SEB) Endogenous superantigens: cell-membrane proteins encoded by certain viruses that infect mammalian cells, e.g., mouse mammary tumor viral (MMTV) protein • Viral or bacterial proteins that bind simultaneously • to particular Vb sequences of TCR and to the a • chain of a class II MHC molecule – induce poly- • clonal T-cell activation & proliferation

41. Programmed Cell Death Is an Essential Homeostatic Mechanism

42. normalapoptotic thymocyte thymocyte

43. AICD: activation-induced cell death TCR-mediated negative selection: Two Pathways to T-cell Apoptosis Fas-associated protein with death domain apoptosis- inducing factor apoptotic protease-activating factor 1