Immunoglobulin%20Structure%20

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Immunoglobulin Structure Function

• Assigned Reading
• Performance Ojectives
• Key terms
• Key Concepts
• Content Outline
• Short Answer Questions

2
Angels Devils
3
Assigned Reading

• Chapter 5 pp107-142
• Janis Kubys Immunology 3rd Ed

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Content Outline

• Basic Structure
• B Cell Receptor
• Antigenic Determinants of Igs
• Immunoglobulin Superfamily
• Ig Classes

• Monoclonal Antibodies (MABS)
• Immunoglobulin Sequencing Studies
• Immunoglobulin Fine Structure

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Background
6
Tiselius
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Electrophoresis
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General Structure of Immunoglobulins

• Electron microscopy
• Crystallography
• Hinge region
• light heavy chains
• binding site
• domains
• fragments

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IgG Crystal
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X - Ray Crystallography

• Crystallized Antigen or Antigen - Antibody
  Complex
• Electron Density Map of the Molecule
• Three Dimensional Images

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Antibodies contain a flexible hinge region

• EM evidence
• Location
• Chemical Structure
• Advantages

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Antibody Flexibility

• EMs of same conc of antibody mixed with different
  conc of antigen
• Ag-Ab complexes form different shapes
• Ag is inflexible
• AB MUST BE FLEXIBLE

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Ag-Ab Complexes
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Immunoglobulin flexible hinge
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Hinge Prolines
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Advantages of hinge

• Rotation around central point
• Bind antigens at various distances
• Bind various ratios of antigens

Blocks or binds to antigens over a wide range of
concentrations
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Structure of IgG
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IgG Domains
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IgG Enzyme hydrolysis
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Ag-Ab complexes after Pepsin
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B Cell Receptor

• BEFORE IMMUNIZATION
• Ig genes are organized Igs assembled
• Anchored on membrane as specific receptors for
  immunogen
• AFTER IMMUNIZATION
• different expression of Ig genes
• lose anchorgtgt secreted
• different class of Ig secreted

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Antigenic Determinants of Igs

• Immunoglobulins are immunogenic
• Inject human antibodies into a mouse
• Mouse develops anti-Human antibodies
• Use these antibodies to probe structure of
  immunoglobulins
• Three classes of anti-antibodies
• Isotypes
• Allotypes
• Idiotypes

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Antibody Classes Outline

• 5 classes of antibodies
• Concentration of classes
• Structure and function of
• IgG
• IgM
• IgA
• IgD
• IgE

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Immunoglobulin Classes

• Immunoglobulin A IgA, mA
• Immunoglobulin D IgD, mD
• Immunoglobulin E IgE, mE
• Immunoglobulin G IgG, mG
• Immunoglobulin M IgM, mM

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Immunoglobuin concentrations
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Ig Superfamily
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IgG Physicochemical Properties

• Molecular weight
• Sedimentation constant 7S
• Total 146,000
• Heavy chain 51,000
• Isotypes 4
• Heavy chain domains 4
• Carbohydrate () 2-3
• half life (days) 21

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Structure of IgG
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IgG Domains
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IgG subclasses
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IgG Functions

• Bind antigen in tissue fluids
• Promote destruction of antigen
• activates complement
• Promote phagocytosis
• binds to Fc receptors on macrophages
• Passive protection of fetus
• binds to receptors on placenta
• transferred to fetal circulation

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Functions of IgG Domains

• VH VL Antigen binding
• CH1 Complement binding c4b
• CH2 complement binding C1q
• CH3 Macrophage binding,Fc receptor
• CH2 CH3 neutrophil K cell binding, bind to
  placental syncytiotrophoblast

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Primary vs Secondary Response
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IgMPhysicochemical Properties

• Molecular weight
• Sedimentation constant 19 S
• Total 900,000
• Heavy chain 65,000
• Isotypes 1
• Heavy chain domains 5
• Carbohydrate () 12
• half life (days) 5

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IgM Structure
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IgM Heavy chains
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IgM Functions

• Antigen receptor for B cell
• Short term protection
• binds tightly to antigen
• (high avidity)

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IgAPhysicochemical Properties

• 
  Serum Secretory
• Molecular weight
• Sedimentation constant 7S 11S
• Total 160,000
  385,000
• Heavy chain 52-56,000
  52,56,000
• Isotypes 2
  2
• Heavy chain domains 4 4
• Carbohydrate () 7-11 7-11
• Half life (days) 6 6

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Structure of IgA
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IgA dimers
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EM of IgA
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Secretion of IgA
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IgA Functions

• Protects body surfaces against invading microbes
• Secretory IgA -
• transported to epithelium
• secreted in mucus, milk tears
• Blood IgA -
• transported to liver
• binds to hepatocytes
• secreted into bile

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J chain

• Small polypeptide chain
• found in polymeric classes of antibodies
• Acts as a clasp to join prototype subunits
• produced by same cell that makes antibodies

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J chain structure
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J chain Beta sheets
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J Chain Barrel
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IgE Physicochemical Properties

• Molecular weight 188,000
• Sedimentation constant 8S
• Total 188,000
• Heavy chain 72,500
• Isotypes 1
• Heavy chain domains 5
• Carbohydrate () 12
• half life (days) 2

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Structure of IgE
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Molecular model of IgE
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IgE Functions

• Mediates inflammatory response
• Immunity to parasitic worms
• Mediates many allergies (type I)

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IgD Physicochemical Properties

• Molecular weight
• Sedimentation constant 7S
• Total 184,000
• Heavy chain 70,000
• Isotypes 1
• Heavy chain domains 4
• Carbohydrate () 9-14
• half life (days) 3

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IgD Structure
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IgD Hinge region
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Substructure of IgD
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Mouse IgD
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Mouse IgD
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IgD Function

• Activation of B cells by antigen
• IgD membrane antigen receptor
• Indicator of Mature B cells
• low levels of IgD IgM in Bone marrow
• high levels of IgD IgM in peripheral lymphoid
  organs

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DONE!!!
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Performance Objectives
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Key Terms

• allotypes, allotypic determinants, Am
  determinants, Gm determinants,
• Km determinants, Bence Jones proteins,
  Antibodies, immunoglobulin classes,
• antibody subclasses, constant region (C), Fab
  fragment, Fab' fragment,
• F(ab')2 fragment, Fc fragment, Framework residues
  (FR), Heavy chain,

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• hinge regions, chimeric antibodies, hybridoma,
  hypervariable regions (HVRs),
• complematrarity determining regions(CDRs)
• Hypoxantinine-Aminoopterin-Thymidine medium
  (HAT),idiotypes, idiotypic determinants,
• immunoglobulin domains immunoglobulins, isotype,
  isotypic determinants,

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• joining chain (J), Light chain, monoclonal
  antibodies, multiple myeloma,
• Secretory Iga, Segmental flexibility, variable
  regions (V)

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Key Concepts

• Distinguish between the overall structure and the
  fine structure of immunoglobulins
• Describe the variable and constant regions of
  immunoglobulins light and heavy chains
• Explain the structural organization of the
  variable regions of an immunoglobulins light and
  heavy chains

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• Differentiate between Hypervariable regions and
  complementarity determining regions
• Contrast monoclonal antibody production vs
  polyclonal antibody production
• Discuss the differences in the biological
  effector functions of the different classes of
  immunoglobulins

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• Diagram the procedure for monoclonal antibody
  production
• Construct a table comparing the biological
  characteristics of the five classes of
  immunoglobulins
• Construct a table comparing the biochemical and
  biophysical characteristics of the five classes
  of immunoglobulins

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Short Answer Questions
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• The analysis of IgG molecules after hydrolysis by
  pepsin and papain led to similar yet different
  results. Explain.
• What is the difference between and immunoglobulin
  and a myeloma protein?
• Why were myeloma proteins and Bence Jones
  proteins critical to the early studies on
  antibody structure? What has largely replaced
  them?

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• Differentiate among, complementarity determining
  regions, hypervariable regions and framework
  regions.
• Explain the statements "Antibodies can be
  antigens" and "Antibodies can be used to
  characterize antibodies".
• Discuss the terms immunoglobulin isotypes,
  immunoglobulin allotypes and immunoglobulin
  idiotypes and give examples of each.

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• Compare conventional antibody production with
  monocloanl antibody production and recombinant
  antibody production.
• What are antibody domains?
• Why can't light chains be used to classify
  antibodies?
• The function of an immunoglobulin molecule is
  related to its structure. Explain.

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• Different cellular fusion products can
  potentially occur in a hybridoma fusion.
• What are the potential products?
• Why are they a problem?
• How can you obtain the appropriate
  combination?
• Distinguish between idiotypes and anti-idiotypes.