Antigen-Independent B Cell Development & Humoral Immune Response

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

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

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 cells plasma 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 • Germinal center: later event • General feature of Ab response

7. 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), highly repetitious molecules, bacterial flagellin bacterial cell-wall polysaccharides with repeating units.

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

11. B cells and humoral immune response • 1. Recognition of the specific Ag • 2. Activation, proliferation, differentiation • Germinal center: later event • 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 Co-sti mol B Th CD40L survive B7 survive

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

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

16. Signal 1 From antigen Signal 2 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 • Activation, proliferation, differentiation • 1) 2-signal activation • 2) signal transduction • Germinal center: later event • General feature of Ab response

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

22. Bruton’s disease 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.

23. 1937，Tiselius use Electrophoresis to analyze the serum proteins Which comprised of 5 components： albumin、a1、a2、b、g globulin anode Antibody，IgG albumin a globulin b globulin g globulin Serum of un-immunized person cathode Electrophoresis

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 • Activation, proliferation, differentiation • 1) 2-signal activation • 2) signal transduction • 3) proliferation • Germinal center: later event • General feature of Ab response

26. Early and late event in Ab response to TD antigen 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

27. （T cell）

28. Affinity maturation

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

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

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. 1、somatic hypermutation 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

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

35. 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. • cytokine determined • occur in single B cell • during RNA transcription • ligation of various C gene • the Vregion of Ig remains, the C region changed

36. With Th’ help Without Th

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

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

39. IgG IgM

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

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

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

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

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

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

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

47. BCR Mitogen receptor

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

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