advanced molecular biology

1. CHAPTER 8
Immunoglobulin:
Structure and Function

2. Learning Objectives
Up on completion of this chapter the student will be able to:
Discuss the general properties of all immunoglobulin's
Describe the basic structure of immunoglobulin's
Relate immunoglobulin structure with function
Define immunoglobulin hypervarialble regions
Define and describe immunoglobulin classes, subclasses,
types and subtypes
Describe B cell receptor
Explain antibody diversity and class switching

3. Outline
8.1. Introduction to Immunoglobulins and antibodies
8.2. General Functions of Immunoglobulins
8.3. Basic immunoglobulin Structure
8.4. Immunoglobulin Fragments: Structure/Function
Relationships
8.5. Human immunoglobulin classes

4. 8.1. Introduction
1. Definition - Molecules that are produced
by the body in response to a foreign
substance and are antagonist to it.
2. They are known as Immunoglobulins
when not referring to their specificity
3. Immunoglobulins reside in the globulin
fraction of serum.
Source: Kuby. Immunology 2007 5th
ed).

5. 8.2. General Functions of Immunoglobulins
 Effector functions (Usually require Ag binding)
 Fixation of complement
 Binding to various cells
• Ag binding
– Can result in protection
– Valence

6.  Immunoglobulin's - heterogeneous
 Myeloma proteins - homogeneous
immunoglobulin's
8.2. General Functions of Immunoglobulins

7.  Heavy & Light
Chains
 Disulfide bonds
 Inter-chain
 Intra-chain
8.3. Basic Immunoglobulin Structure
CH1
VL
CL
VH
CH2 CH3
Hinge Region
Carbohydrate
Disulfide bond
Source: Kuby. Immunology 2007 5th
ed).

8.  Variable &
Constant Regions
 VL & CL
 VH & CH
 Hinge Region CH1
VL
CL
VH
CH2 CH3
Hinge Region
Carbohydrate
Disulfide bond
8.3. Basic Immunoglobulin Structure
Source: Kuby. Immunology 2007 5th
ed).

9.  Domains
 VL & CL
 VH & CH1 - CH3
(or
CH4)
 Oligosaccharides
CH1
VL
CL
VH
CH2 CH3
Hinge Region
Carbohydrate
Disulfide bond
8.3. Basic Immunoglobulin Structure
Source: Kuby. Immunology 2007 5th
ed).

10. Immune serum
Ag adsorbed serum
α1 α2 β γ
+ -
albumin
globulins
Mobility
Amount
of
protein
Antibodies
Source: Kuby. Immunology 2007 5th
ed).

11. Five Immunoglobulin Classes;
IgG, IgA, IgM, IgD, & IgE
Fab, Disulphide bonds Hinge, Domains,
Variable regions, Constant regions,
COOH end, NH3 end, Binding site
Antibodies
Source: Kuby. Immunology 2007 5th
ed).

12. 1. Genetic Variation in Antibody Heterogeneity
 Isotypes
 Allotypes
 Idiotypes
2. Properties
 C’ Fixation
 Placental transfer
Antibodies
Source: Kuby. Immunology 2007 5th
ed).

13. (a) Isotypic determinants are constant region determinants that
distinguish each Ig class and subclass within a species.
(a) Allotypic determinants are subtle amino acid differences
encoded by different alleles of isotype genes. Allotypic
differences can be detected by comparing the same antibody
class among different inbred strains.
(a) Idiotypic determinants are generated by the conformation of
the amino acid sequences of the heavy- and light-chain
variable regions specific for each antigen. Each individual
determinant is called an idiotope, and the sum of the
individual idiotopes is the idiotype.
Antibodies

14. Source: Kuby. Immunology 2007 5th
ed).

15. 8.4. Immunoglobulin Fragments:
Structure/Function Relationships
 Fab
 Ag binding
 Valence = 1
 Specificity
determined by VH
and VL
Papain
Fc
Fab
• Fc
– Effector functions
Source: Kuby. Immunology 2007 5th
ed).

16. Ag Binding
Complement Binding Site
Placental Transfer
Binding to Fc
Receptors
8.4. Immunoglobulin Fragments:
Structure/Function Relationships
Source: Kuby. Immunology 2007 5th
ed).

17.  Fab
 Ag binding
 Fc
 Effector functions
 F(ab’)2
Pepsin
Fc
Peptides
F(ab’)2
8.4. Immunoglobulin Fragments:
Structure/Function Relationships
Source: Kuby. Immunology 2007 5th
ed).

18. 8.5. Human Immunoglobulin Classes
 IgG - Gamma (γ) heavy chains
 IgM - Mu (µ) heavy chains
 IgA - Alpha (α) heavy chains
 IgD - Delta (δ) heavy chains
 IgE - Epsilon (ε) heavy chains

19. Human immunoglobulin sub classes
IgG Subclasses
 IgG1 - Gamma 1 (γ1) heavy chains
 IgG2 - Gamma 2 (γ2) heavy chains
 IgG3 - Gamma 3 (γ3) heavy chains
 IgG4 - Gamma 4 (γ4) heavy chains
IgA subclasses
 IgA1 - Alpha 1 (α1) heavy chains
 IgA2 - Alpha 2 (α2) heavy chains
8.5. Human Immunoglobulin Classes

20. Human immunoglobulin light chain types
Kappa (κ)
Lambda (λ)
8.5. Human Immunoglobulin Classes

21. Human immunoglobulin light chain subtypes
Lambda light chains
 Lambda 1 (λ1)
 Lambda 2 (λ2)
 Lambda 3 (λ3)
 Lambda 4 (λ4)
8.5. Human Immunoglobulin Classes

22. Immunoglobulin’s
Nomenclature
 IgM (kappa)
 IgA1(lambda 2)
 IgG
Heterogeneity
8.5. Human Immunoglobulin Classes

23. Antibodies - Properties

24.  Structure
 Monomer (7S)
IgG1, IgG2 and IgG4 IgG3
IgG
Source: Kuby. Immunology 2007 5th
ed).

25. IgG
 Characteristics
 150,000 MW
 Highest serum conc.
 Transported across placenta
via Fc - relevant to Lab
diagnosis of ID, Laboratory
false positive serologies
 Four subclasses (IgG1-4)
 Monomeric in form
Source: Kuby. Immunology 2007 5th
ed).

26.  Characteristics
 Dimer, monomer
 Two subtypes (1,2)
 Secretions
 Tears, Saliva, GI tract, Colostrum
 Secretory IgA has Secretory component made by
epithelial cells, that protects it from enzymatic and other
chemical degradation
 It prevents viral and some bacterial attachment to
mucosal epithelial cells
 Dimeric form has J chain – connects
IgA
Source: Kuby. Immunology 2007 5th
ed).

27.  Characteristics
 Pentameric form
 Primary response
 Role in Lab Diagnostics
 Does not pass placenta
 Effective agglutinator
 Most efficient C’ fixation
IgM
Cµ4
J Chain
Source: Kuby. Immunology 2007 5th
ed).

28. Fixation of C1 by IgG and IgM Abs
C1r C1s
C1q
C1r C1s
C1q
No activation Activation
Source: Kuby. Immunology 2007 5th
ed).

29.  Characteristics
 Extra Constant region domain (C4)
 Lowest serum concentration
(meaning to diagnostic Lab tests)
 Binds to Mast cells via Fc - Allergic
reactions
 Protection - Parasitic infections
IgE
Source: Kuby. Immunology 2007 5th
ed).

30.  Low concentration in serum (<1%)
 Function largely unknown - may act as Antigen receptor for
B cells
 No clinical need to measure - clue to physician competence
& clerical error
IgD

31. Antibody - Antigen Interactions
 Antibody binding site
 Folded structure - forming cleft between
Heavy and Light chains - tertiary
 Apple analogy - best fit
 Antigen binding site
 Quite small (6 amino acids)
 Epitope
 Sequential vs. Conformational -
Implications to Lab tests
Source: Kuby. Immunology 2007 5th
ed).

32. Outcomes to Antibody Binding
1. Agglutinates Ag
2. Initiates immune response
1. Cellular
2. Humoral
3. Activates Complement
4. Cleared/Killed by
phagocytic system
Source: Immunobiology 2001 5th
ed).

33. Summary
 An antibody molecule consists of two identical light chains
and two identical heavy chains, which are linked by
disulfide bonds. Each heavy chain has an amino-terminal
variable region followed by a constant region.
 In any given antibody molecule, the constant region
contains one of five basic heavy-chain sequences (α,,γ, 
or ) called isotypes and one of two basic light-chain
sequences ( or к) called types.
 The heavy-chain isotype determines the class of an
antibody (, IgM; γ, IgG; , IgD; α, IgA; and , IgE).

34. Review questions
Explain the general properties of all immunoglobulin's
Draw roughly basic structure of immunoglobulin's and label
it correctly
Discus immunoglobulin structure with function
Define and describe immunoglobulin classes, subclasses,
types and subtypes
Explain antibody diversity and class switching

35. Reference
1. Kuby; Goldsby et. al. Immunology. 2007 (5th
ed)
2. Tizard. Immunology an introduction,4th
edition ,Saunders publishing,1994
3. Naville J. Bryant Laboratory Immunology and Serology 3rd
edition.
Serological services Ltd.Toronto,Ontario,Canada,1992
4. Abul K. Abbas and Andrew H. Lichtman. Cellular And Molecular
Immunology 2008, 5th
edition
5. Mary T. Keogan, Eleanor M. Wallace and Paula O’Leary Concise clinical
immunology for health professionals , 2006
6. Ivan M. Roitt and Peter J. Delves Essential immunology 2001, 3rd
ed
7. Reginald Gorczynski and Jacqueline Stanley, Clinical immunology 1990.