1. Chapter 8 The Development and Survival of Lymphocytes

2. - Positive selection : self antigen + lymphocyte receptors weak interaction survival signal establishment of repertoire for foreign antigens -Negative selection : self antigen + lymphocyte receptors strong interaction death signal removal of self reactive repertoire establishment of immunological tolerance

3. Development of B lymphocyte -B cell development Figure 8.1 -Lymphocytes derive from a ‘early lymphocyte progenitor’ Figure 8.2 -Intrinsic developmental program requires signals from specialized microenvironments -stromal cell → interact with the developing lymphocytes → provide signals by growth factors and cell surface molecule

8. The early stages of B cell development are dependent on bone marrow stromal cells Figure 8.3 - stromal cell → Flt3 ligand ↔ Flt3 → IL-7 → SCF ↔ Kit → CXCL12 (SDF-1) → TSLP (?) - The common lymphoid progenitor gives rise to the earliest B-lineage cells, the pro-B cell

10. A definitive B-cell fate is specified by induction of E2A (E12 and E47) and EBF - PU.1 and Ikaros → E2A → EBF → the pro-B cell state - IL7 : promoters the survival of commited progenitors - As B-lineage cells mature, they migrate within the marrow, remaining in contact with the stromal cells. - The final stages of development of immature B cells into mature B cells occur in peripheral lymphoid organs such as spleen

11. B cell development bigins by rearrangement of the heavy-chain locus Figure 8.4 - E2A and EBF RAG-1 and RAG-2 Pax5 → CD19, Ig , BLNK - Sequential cell surface molecule Figure 8.5 - Pro B ⇒ the production of intact μ heavy chain ( pro B cell that do not produce a μ chain → eliminated ) ⇒ Pre B cell - In at least 2 out of 3 case, the first V H to DJ H rearrangement is non productive ⇒ A rough estimate of the chance of generating a pre-B cell : 55%, (1/3 + (2/3 x 1/3)) = 0.55 D-J early at both alleles V-DJ late on one chromosome

14. The pre-B cell receptor - Pre B cell receptor H chain + a surrogate light chain ↓ pre B cell receptor Figure 8.6 ↓ Ig , Ig  pre B cell receptor complex : an important checkpoint in B cell development - Pre B cell receptors → interaction of each other → formation of dinner or oligomers → signaling → no more H chain gene rearrangement → become IL-7 senstive → cell proliferation → the large pre-B cells 5 V pre B Figure 8.7 E2A and EBF

17. Pre-B cell receptor signaling inhibits further heavy-chain locus rearrangement and enforce allelic exclusion Figure 8.8 - allelic exclusion : only one of the two alleles of a gene is expressed - Signaling from the pre B cell receptors ⇒ promotion of H chain allelic exclusion · reducing the expression of RAG-1 and RAG-2 · further reducing levels of RAG-2 by its phosphorylation and degradation · reducing access of the heavy-chain locus to the recombinase machinery - In the absence of pre-B cell receptor signaling ⇒ no allelic exclusion e.g. 5 knockout mice ⇒ rearrangements of the heavy chain genes on both chromosome

19. Pre-B cells rearrange the light-chain locus and express cell surface immunoglobulin - large pre B cell resting small pre B cell RAG1, RAG2 reactivation different Light chain gene rearrangement ⇒ BCR diversity - multiple successive L chain gene rearrangement ⇒ The chance of generating an intact light chain is very high Figure 8.9 ⇒ immature B cells Several Division (30~60 fold)

21. -The expression of proteins regulating Ig gene rearrangement and function is developmentally programmed Figure 8.10 -The stages of B cell development up to the point of assembly of a complete surface Ig : Figure 8.11 ⇒ the point at which developing B cell can be lost as a result of failure to produce a productive join - Isotypic exclusion : the production of a light chain from  or gene

24. Immature B cells are tested for auto reactivity before they leave the bone marrow - Immature B cell → tested for tolerance to self antigens in the bone marrow → establishment of central tolerance → escape → mature in the periphery → removed by self antigens → establishment of peripheral tolerance ⇒ Figure 8.12

26. -receptor editing Figure 8.13 : self-reactive B cell might be rescued by further light chain gene rearrangement e.g. transgenic mice ⇒ replace the autoreactive light chain transgene with a non-autoreactive gene (strong cross-linking of sIgM → RAG expression) -immature B cell + self antigens of low valence (soluble protein) ⇒ weak interaction ⇒ a state of permanent unresponsiveness : anergy ⇒ not immediately die ⇒ die later on ⇒ can not be activated with help from antigen specific T cells ⇒ signal transduction is blocked -immature B cell + self antigens with a weak but definite affinity ⇒ very weak interaction or no interaction ⇒ no change : ignorance ⇒ can be activated ⇒ cause autoimmune disease

31. T cell development in the thymus Figure 8.14 - thymus structure cortex medulla thymic stroma : a network of epithelial cells - progenitor cell T cell lineage - The cortex : immature thymocytes, macrophage - The medulla : mature thymocytes, dendritic cell, macrophage - The importance of thymus in T cell development thymectomy DiGeorge ’ s syndrome nude mice Notch signal from stromal cell Figure 8.16 Figure 8.15 T cell development in the thymus

37. -experiments in nude and SCID mice Figure 8.17 nude : thymus defect SCID : no gene rearrangement → lymphocyte defect -most developing T cells die in the thymus 5 X 10 7 cell generation each day ↓ Figure 8.18 10 6 ~ 2 X 10 6 leave the thymus each day

43. Successive stages in the development of thymocytes - lymphoid progenitors in the bone marrow ↓ the thymus Double negative (CD3-CD4-CD8-) (60% of thymocyte)  T cell major  cell minor CD4 T cells CD8 T cells  T cell NKT double (  ) positive single positive Figure 8.19

45. - The  pathway kit and CD44 expression in DN1 cells ↓ CD25 expression (DN2), Figure 8.20 reduced kit and CD44 expression (DN3) ↓  Chain gene rearrangement (DN2 → DN3) ↓ expression of  chain loss of CD25 expression ↓ expression of a surrogate pre T cell receptor  chain, pT  (DN3) ↓ pre T cell receptor + CD3 complex expression ↓ proliferation (DN4) with dimerization of pre-TCR

47. ↓ no more  chain gene rearrangement CD4 and CD8 expression proliferation ↓ no more proliferation  chain gene rearrangement (multiple successive rearrangement) low levels of TCR proliferate die mature Small Double positive thymocytes large double positive (CD4 +, CD8 + ) thymocytes no self MHC + peptide Self MHC + peptide

48. ↓ high level of TCR either CD4, CD8 expression ↓ ↓ Survive die ↓ exit to the periphery no self MHC + peptide self MHC + peptide single positive thymocyte

49. Distinct part of thymus progenitors from the bone marrow enter at the cortico-medullary junction Figure 8.21 ↓ large immature double negative thymocytes at the outer edge of the cortex ↓ Small immature double positive thymocytes at the deeper cortex ↓ single positive cell in the medullar -Cortical epithelial cell : MHC class I and MHC class II expression ⇒ positive selection -dendritic cell in the medulla : MHC class I and II expression ⇒ negative selection

51. T cells with  or  receptors arise from a common progenitor - The ,  and  loci undergo rearrangement simultaneously in developing thymocytes pre TCR  TCR  TCR Figure 8.22

55.  T cell arise in an ordered sequence early in life - The first T cells to appear during embryonic development carry  TCR Figure 8.23 -In mice,  T cell first appear in discrete waves with the T cells in each wave populating distinct sites the epidermis : dendritic epidermal T cell Figure 8.24 the reproductive tract intestinal epithelium, lymphoid organs