1. B cell subsets and development Fetus liver ： B1 B Bone Marrow ： HSC proB preB imB mB spleen ： NF B FP FO B MZ B Antigen-independent development of B cells

2. three major naive peripheral B-cell populations B cell Immunol Rev 2004; 197:206 High-affinity IgG

3. INSTITUTE FOR IMMUNOBIOLOGY B cell and B cell-mediated humoral immune response Part II Department of Immunology Fudan University Wei Xu, Ph.D 021-54237749 wx2362@hotmail.com

4. Overview of the humoral immune response against bacterial B cellsplasma cells

5. Significance of humoral immunity eliminate extracellular bacterium and toxin eliminate extracellular virus

6. B cells and humoral immune response 1. Recognition of the specific Ag 2. Activation, proliferation, differentiation 2.Germinal center: later event 3.General feature of Ab response

7. highly repetitious molecules, bacterial flagellin bacterial cell-wall polysaccharides with repeating units. thymus-dependent (TD) antigens B response to TD Ag requires direct contact with Th cells, thymus-independent (TI) antigens TI- 1 Ag TI-2 Ag bacterial cell-wall components, lipopolysaccharide (LPS),

8. Recognition of TD Ag Directly recognize Ag (B cell epitope) No MHC involvement surfaced displayed B cell-epitopes

9. Ab (BCR) binds the B-cell epitope directly, TCR binds with a self-MHC-T-cell-epitope complex

10. B cell activation B cell epitope BCR-Ig  /Ig  -coreceptor complex B cell epitope BCR Iga/b Signal + Ag-C3d CR2 CD19 Signal + +++ （ CD21-CD19-CD81 ） coreceptor

11. B cells and humoral immune response 1. Recognition of the specific Ag 2. Activation, proliferation, differentiation 2.Germinal center: later event 3.General feature of Ab response

12. 1) activation A. 2-signal activation model B. the help from Th cell 2) Signal transduction 3) Proliferation and differentiation

13. the 2-signal rule signal 1 ： BCR － B cell epitope signal 2 ： CD40 － CD40 L B Th Co-sti mol CD40L survive B7 survive

14. B cell activation requires 2 signals Signal 3: IL-4

15. Signal 1From antigen BCR serves 2 roles: 1.Ag-induced clustering of BCRs delivers signals that initiate the activation process. 2.BCR internalize the Ag into endosome, process and present on surface for T recognition Receptor-mediated Ag endocytosis T cell epitope-MHC II presentation B cell epitope Recognition of

16. Signal 2 Signal 1 From antigen From Th Signal 3 From Th

17. Antigen crosslinks mIg(BCR), generating signal 1, which leads to increased expression of class II MHC and costimulatory B7. Antigen–BCR complexes are internalized by receptor-mediated endocytosis and degraded to peptides, which are bound by class II MHC and presented as peptide–MHC complexes. Th cell recognizes Ag–class II MHC and B7-CD28 co-stimulation on B- cell membrane which activates TH cell. Th cell begins to express CD40L. Interaction of CD40 and CD40L provides signal 2. Th cell release large quantities of cytokines( IL-4 ) signal 3 to support the progression of the B cell replication and differentiation.

18. Signal 3 Th-secreting cytokines Regulate B cell differentiation

19. B cells and humoral immune response 1. Recognition of the specific Ag 2.Activation, proliferation, differentiation 1) 2-signal activation 2) signal transduction 2.Germinal center: later event 3.General feature of Ab response

20. PTK Src family immunoreceptor tyrosine-based activation motif (ITAM) Tyrosine kinase phosphorylation cascade

22. a genetically determined immunodeficiency disease inability to synthesize all classes of antibody. discovered in 1952 by O. C. Bruton. Case: a young boy who had mumps 3 times and experienced 19 different episodes of serious bacterial infections during 4 years. Do not raise Abs to any vaccines. Bruton’s disease

23.  globulin  globulin  globulin 1937 ， Tiselius use Electrophoresis to analyze the serum proteins Which comprised of 5 components ： albumin 、  1 、  2 、  、  globulin Antibody ， IgG albumin Serum of un- immunized person Electrophoresis cathode anode

24. Pathogenesis: failures in B-cell development. inhibition pro–B to pre–B-cell transition In 1990s, the gene was cloned which encodes Bruton’s tyrosine kinase (Btk). Btk play important roles in B-cell signaling vital to the function of mature B cells Absence of Btk results in the failure of B activation and Ab generation

25. B cells and humoral immune response 1. Recognition of the specific Ag 2.Activation, proliferation, differentiation 1) 2-signal activation 2) signal transduction 3) proliferation 2.Germinal center: later event 3.General feature of Ab response

26. Early events ： follicle （ B ） -paracortex （ T ） border, B activation and T-B activation Small amounts of Ab production Late events ： At the germinal center Presence of Ag and Th Affinity maturation Ig class switch (IgM IgG) Memory B Early and late event in Ab response to TD antigen

27. （ T cell ）

28. Affinity maturation

29. 1 、 somatic hypermutation 2 、 affinity maturation 3 、 Ig class switch AgTh late event in Ab response to TD antigen in LN

30. Dark zone Light zone （ mantle zone ） Un-activated lymphocytes

31. Follicular DC (FDC) No MHC II Bind with Ag-Ab （ IC ） by FcR ， maintain Ag for long Provide persistent Ag signal for B cells

32. In presence of Ag, by Th’s co-stimulation Point Mutation of CDR in the Ig V region Affinity-enhanced BCR(B cell) is selected affinity maturation 1 、 somatic hypermutation

34. 2 、 affinity maturation Result of somatic hypermutation of B cell B cells with high affinity would survive Affinity enhancement

35. cytokine determined occur in single B cell during RNA transcription ligation of various C gene the V region of Ig remains, the C region changed 3 、 Ig class (isotype) switch In response to CD40-CD40L signal and IL-4 from Th cell, the activated B cells undergo the process of heavy chain isotype (class) switching leading to production of Abs with different class of heavy chain.

36. Without Th With Th’ help

37. Th cell-secreting cytokines determines the Ig class switch

38. CD40L signal 、 IL-4 from Th No Th The V gene would recombine with a downstream C region gene and the other DNA deleted

39. IgM IgG

40. 1 、 somatic hypermutation 2 、 affinity maturation 3 、 Ig class switch (Th’s help) AgTh late event in Ab response to TD antigen in BM

41. 5) Fate of the activated B cell plasma cell ， PC move to BM? Secret high level of Abs move to BM? Secret high level of Abs memory B cell maintain in BM? Never die? maintain in BM? Never die?

42. follicular B plasma cells short-lived form a germinal centre plasma cells 1 ． plasma cell follicle long-lived plasma cell Bone Marrow marginal-zone B plasma cells Bm Early stage Th later

43. Formation of plasma cells Nat Rev Immunol 2005; 5:232

44. plasma cells crucial survival signals (BM) BAFF- BCMA IL-6- IL-6R Long-lived plasma cells in the bone marrow 内皮细胞选择素 血管细胞黏附分子 retention of plasma cells in BM somatic mutation class-switch CXCR4 B-cell- activating factor survival signals BCMA ： receptor B-cell maturation antigen Germinal Center

45. B cell response to TI antigen CD5 ＋ B1 Low-affinity IgM No help from Th No class switch (no IgG)

46. Signal 1 ： Ag Signal 2 ： mitogen Mitogen receptor Polyclonal strong B activation

47. Mitogen receptor BCR

48. Signal 1 ： cross-linking of lots of BCR By polymeric saccharide B cell response to TI-2 antigen Repetitive units

49. B cells and humoral immune response 1. Recognition of the specific Ag 2. Activation, proliferation, differentiation 2.Germinal center: later event 3.General feature of Ab response

50. The general feature of humoral immunity primary response Mostly IgM with low affinity ， IgG secondary response Mostly IgG with high affinity and high level

51. primary immune response ① lag phase: long 5 － 10 days ② log phase ③ plateu phase short ④ decline phase quickly Mostly IgM, later IgG, low level and affinity

52. secondary immune response ① long Lag phase: short, 1-3 days ， quickly to the top ② strong The Ab level is 10 times more than that of the primary response ③ most IgG enhanced affinity mB act as APC ， with high mB7 ， and high-affinity BCR, small amounts of Ag can stimulate mB

53. 5-10 days1-3 days

56. 4 、 受体修正 (receptor revision) 生发中心内 识别自身抗原的 B 细胞 发生 Ig V(D)J 基因的二次重排， 使 BCR 被修正为针对非自身抗原。 清除自身反应性 B 细胞 使针对外来抗原的 BCR 具有更广泛的多样性。

57. Where do Th and B cell encounter ？ follicle （ B ） -paracortex （ T ） boundary

58. （ T cell ）

59. Ag 特异性 T （蓝色） 向滤泡边缘移动 Ag 特异性 B （蓝色） 向滤泡边缘移动 Ag 特异性 T （棕色） Ag 特异性 B （蓝色） 在滤泡边缘相遇 滤泡区： B T 副皮质区： T B