Immunoglobulins are glycoprotein molecules produced by plasma cells in response to antigens that function as antibodies. They have a basic structure consisting of two heavy chains and two light chains held together by disulfide bonds, forming variable and constant regions. The variable regions determine antigen binding specificity, while the constant regions determine effector functions. The five major classes in humans are IgG, IgM, IgA, IgD, and IgE, which have different structures, properties, and functions in the immune response.
2. Immunoglobulins:Structure and
Function
Definition: Glycoprotein molecules that
are produced by plasma cells in response
to an immunogen and which function as
antibodies
+ -
Amount of protein
albumin
globulins
1 2 Immune serum
Ag adsorbed serum
Mobility
3. General Functions of
Immunoglobulins
• Ag binding
– Can result in protection
– Valency
Effector functions
Fixation of (Usually require Ag binding)
complement
Binding to various
cells
5. Immunoglobulin Structure
Disulfide bond
Heavy & Light
Chains Carbohydrate
Disulfide bonds
Inter-chain CL
VL
Intra-chain
CH2 CH3
CH1
Hinge Region
VH
6. Immunoglobulin Structure
Disulfide bond
Variable & Carbohydrate
Constant
Regions CL
VL
VL & CL
CH2 CH3
VH & CH CH1
Hinge Region
VH
Hinge Region
7. Immunoglobulin Structure
Disulfide bond
Domains
VL & C L Carbohydrate
VH & CH1 - CH3
(or CL
CH4) VL
CH2 CH3
Oligosaccharides CH1
Hinge Region
VH
8. IgG molecule
Used with permission from: Dr. Mike Clark, Immunology
Division, Department of Pathology Cambridge University,
Cambridge, England
9. Structure of the Variable Region
Hypervariable (HVR) or complimentarity
determining regions (CDR) HVR3
150
Variability Index
100 HVR2
HVR1
50
FR1 FR2 FR3 FR4
0 25 50 75 100
Amino acid residue
Framework regions
13. Human Immunoglobulin
Classes
IgG - Gamma heavy chains
IgM - Mu heavy chains
IgA - Alpha heavy chains
IgD - Delta heavy chains
IgE - Epsilon heavy chains
14. Human Immunoglobulin
Subclasses
IgG Subclasses
IgG1 - Gamma 1 heavy chains
IgG2 - Gamma 2 heavy chains
IgG3 - Gamma 3 heavy chains
IgG4 - Gamma 4 heavy chains
IgA subclasses
IgA1 - Alpha 1 heavy chains
IgA2 - Alpha 2 heavy chains
19. IgG
Structure
Properties
Major serum Ig
Major Ig in extravascular spaces
Placental transfer – Does not require Ag binding
(IgG2)
Fixes complement (IgG4)
Binds to Fc receptors (IgG2, IgG4)
Phagocytes - opsonization
K cells - ADCC
21. IgM
Structure
Properties
3rd highest serum Ig
First Ig made by
fetus and B cells
Fixes complement
22. Fixation of C1 by IgG and IgM Abs
C1r C1
s
C1q
C1r C1
s
C1q
No activation Activation
23. IgM
Structure
Properties
3rd highest serum Ig
First Ig made by fetus
and B cells
Fixes complement
Agglutinating Ig
Binds to Fc receptors Tail
Piece
B cell surface Ig
27. IgA
Structure
Properties
2nd highest serum Ig
Major secretory Ig (Mucosal or Local
Immunity)
Tears, saliva, gastric and pulmonary
secretions
Does not fix complement (unless
aggregated)
Binds to Fc receptors on some cells
31. IgE
Structure
Properties
Least common serum Ig
Binds to basophils and mast cells (Does not
require Ag binding)
Allergic reactions
Parasitic infections (Helminths)
Binds to Fc receptor on eosinophils
Does not fix complement