1. Section 4

2. Outline Outline  Introduction  Structure of Immunoglobulin  Function of Immunoglobulin  Characteristics and Functions of 5 Ig Classes of 5 Ig Classes  Monoclonal Antibody (conception of Ab and Ig)

3. An enormous family of related, but nonidentical glycoproteinsAn enormous family of related, but nonidentical glycoproteins

6. Expression of Ig membrane Ig, mIg : expressen on the surfaces of resting B lymphocytes, as receptormembrane Ig, mIg : expressen on the surfaces of resting B lymphocytes, as receptor secreted Ig, sIg : as antibody(Ab)secreted Ig, sIg : as antibody(Ab)

7. Major functions of Ig Binding AgBinding Ag Secondary biologic activitiesSecondary biologic activities –Opsonins –Activate the complement cascade –Cross the placental barrier

8. Chapter 1 organization of organization of immunoglobulins immunoglobulins

10. Molecular structure of Ig An enormous family of related, but nonidentical glycoproteinsAn enormous family of related, but nonidentical glycoproteins Ab are bifuctional molecules:Ab are bifuctional molecules: bind specifically to Ag bind specifically to Ag secondary phenomena secondary phenomena

11. The four-chain basic unit Symmetrical structure  Two Heavy (H) chains, about twice as large as the L chain  Two Light (L) chains, the smaller  Covalent interchain disulfide bridges

13. (Ag-biding site) L chain H chain (,,,,)(,,,,) V region C region  H2L2 H2L2 H2L2 H2L2  hinge region  2 regions κ/λ (2:1) Monomer of Ig

14. domains  Both H and L chains contain folded globular domains  Each domains has a single intrachain disulfide bond  L chains always contain two domains  H chains contain either 4 or 5 domains

16. Immunoglobulin variable regions and constant regions variable region (V region) The sequences of the N-terminal The sequences of the N-terminal domain in a heavy- or light-chain polypeptide are variable – V H – V L

17. constant region (C region) The sequences of the other domains remain relatively constantThe sequences of the other domains remain relatively constant –C H –C L L-chain polypeptides contain only a C L domainL-chain polypeptides contain only a C L domain H-chain polypeptides contain 3 or more C H domainsH-chain polypeptides contain 3 or more C H domains

18. （二）可变区和恒定区

19.  The V H is juxtaposed with the V L to form an Ag-binding site  Each monomer of Ig contains two Ag-binding sites

21. Hinge region  Located between the CH1 and CH2 of the H chains in most Ig  Permits flexibility between the two Fab arms of Ab  Allows the two arms to open and close to accommodate binding to two epitopes

22. Flexibility of immunoglobulins

24. Hypervariable regions The V regions contain two regions:  Framework regions----relatively invariant  Hypervariable regions----extremely variant Complementarity-determining regions (CDRs)

25. Complementarity-determining regions (CDRs) Each VH and VL contains 3 CDRs

29. Antigen-binding Can Take Many Forms – Best Method

30. J chain  IgM and IgA generally exist as polymers  Joint  Joint monomers to form polymers n(H 2 L 2 ) n(monomer) n(H 2 L 2 ) n(monomer) J chain (H 2 L 2 )n J polymer polymer J chain and secretary component

33. Secretory component Associated only with IgA and is found almost exclusively in body secretionsAssociated only with IgA and is found almost exclusively in body secretions

35. Enzymatic digestion products of Ig Be most susceptible to cleavage near Be most susceptible to cleavage near the hinge region Enzyme papainEnzyme papain Enzyme pepsinEnzyme pepsin

36. Enzyme papain Splits an Ig into 3 fragments of Splits an Ig into 3 fragments of roughly similar size

38. Fab region: each Fab is monovalent with respect to Ag-binding activity Fab region: each Fab is monovalent with respect to Ag-binding activity Fc region:  be recognized by the Fc receptors found on many types of cells  Determine most of the secondary biologic properties of Ig

39. Enzyme pepsin Splits an Ig into:  A single large fragment ----F(ab) ’ 2 fragment  PFc ’

41. F(ab) ’ 2 fragment: roughly corresponds to 2 disulfidelinked Fab fragmentsroughly corresponds to 2 disulfidelinked Fab fragments Has divalent Ag-binding activityHas divalent Ag-binding activity PFc ’ : Extensively degradedExtensively degraded Usually does not survive as an intact fragmentUsually does not survive as an intact fragment

42. Hydrolytic fragment of Ig 2 Fab + 1Fc 1 F(ab ’ ) 2 +pFc’ (papain)(pepsin)

43. Chapter 2 Ig classes and Ig classes and subclasses subclasses

44. Ig classes, subclasses and types Classes and subclasses are determined on the basis of CHClasses and subclasses are determined on the basis of CH According to CH sequences and their physical and biologic propertiesAccording to CH sequences and their physical and biologic properties

45. Classes Humans express five different classes of Ig heavy chainsHumans express five different classes of Ig heavy chains All of the heavy chains in any given Ig are identicalAll of the heavy chains in any given Ig are identical

46. The classes of heavy chains γ μ α δ ε γ μ α δ ε The classes of Ig containing these CH IgG IgM IgA IgD IgE IgG IgM IgA IgD IgE The μ and ε contain 5 CH The γ, α and δ contain 4 CH

48. Subclasses or subtypes IgG1, IgG2, IgG3, IgG4IgG1, IgG2, IgG3, IgG4 IgA1, IgA2IgA1, IgA2

49. CH of all Ab molecules of one CH of all Ab molecules of one isotype of subtypes have essentially isotype of subtypes have essentially the same amino acid sequence the same amino acid sequence

50.  All light chains can be classified into 2 types according to CL sequence Kappa (κ)Kappa (κ) lambda (λ)lambda (λ)  No known functional differences exist between two typs  An Ab molecule has either 2 κ or 2 λ light chains, but never one of each

51. Isotypes, allotypes and idiotypes of Ig Ig are proteinsIg are proteins Ig can be immunogenicIg can be immunogenic –Isotypic----isotype –Allotypic----allotype –Idiotypic----idiotype

52. isotypes  The antigenic features of a class of Ig H  The genes for isotypic variants are present in all healthy members isotype

53. allotypes  Vary among individuals within a species and are under genetic control allotypes

54. idiotypes The unique V-region amino acid sequences of the homogeneous Ig molecules produced by a single B cell cloneThe unique V-region amino acid sequences of the homogeneous Ig molecules produced by a single B cell clone idiotype

56. Membrane and secreted Ig membrane Ig, mIg : expressen on the surfaces of resting B lymphocytes, as receptormembrane Ig, mIg : expressen on the surfaces of resting B lymphocytes, as receptor secreted Ig, sIg :secreted Ig, sIg : as antibody(Ab) as antibody(Ab)

57. Chapter 3 biological activities of Ig biological activities of Ig

58. Activities of variable regions Bind to Ag in vivo or in vitro---resistant to infection by:  Opsonizing (coating) organisms  Bind to viruses, prevent invation  Neutralize toxins of microorganisms

59. 返回

60. Neutralization By Antitoxin Antibodies

61. Neutralization By Antiviral Antibodies

62. Bacterial ‘Neutralization’ By Ab

63. Activities of constant regions Complement fixationComplement fixation OpsonizationOpsonization ADCCADCC

64. Complement fixation  Ag-bound IgM and IgG can initiate the classical pathway of complement activation  Activated complement mediated lysis of the pathogen (or other cell)

66. Opsonization  IgG is an opsonizing Ab  Fc confers the opsonizing property  Many phagocytic cells bear receptors of the Fc region of IgG Macrophages Polymorphonuclear phagocytes phagocyte

67. 调理作用 Opsonization

69. ADCC

70. Fc  RIII CD16 Antibody Marks Target Cells For NK Cell Attack (ADCC)

72. Chapter 4 biological properties and functions of Ig classes biological properties and functions of Ig classes

73. IgG  About 75% of the total serum Ig in normal adults  The most abundant Ab produced during secondary IR  The only class of Ig that can cross the placenta  Be capable of fixing serum complement  Bind the Fc receptors

74. IgA In secretions: SIgA ---- dimerIn secretions: SIgA ---- dimer On B cell surfacesOn B cell surfaces monomer monomer In the bloodIn the blood

76.  The predominant Ig produced by B cells in submucosal lymphoid tissues  The most abundant Ab class found in secretions (milk, bronchial secretions, intestinal mucus)

77. IgM  Pentamer in serum  Predominate in early primary immune responses  The most efficient complement fixing Ig  Expressed on the surfaces of B cells, particularly na ï ve B cells

78.  Can be synthesized during the late embryo stage  The first Ig produced in primary immune responses  Natural blood group antibody

82. IgD  The physiologic function of IgD is unknown  Rarely secreted in significant amounts in blood  Commonly found on the surfaces of B cells

83. mIgMmIgD 成熟 B 细胞活化 B 细胞未成熟 B 细胞  mIgD can bind Ag and transmit signals to the cell interior  When B cells containing mIgD become activated, mIgD expression ceases

84. IgE  Represents only a minute fraction of all serum Ab  Has central involvement in allergic disorders  In monomeric form

85. Fc  RI IgE Antibody Binds To Mast Cells & Basophils To Arm Them For Mediator Release

86. Chapter 5 Ab technology Ab technology

87. Poly-clonal abtibody, PcAb The antiserum from an animal The antiserum from an animal immunized against an immunogen is a immunized against an immunogen is a complex mixture of structurally diverse complex mixture of structurally diverse Abs recognizing multiple epitopes on Abs recognizing multiple epitopes on the immunogen, and its composition the immunogen, and its composition fluctuates unpredictably over the life of fluctuates unpredictably over the life of the animal the animal

88. 带有多个表位 抗原 针对不同表位 的 B 细胞 克隆增殖 多种抗体的混合物 （多克隆抗体） 刺激小鼠

89. Mono-clonal antibody,McAb