Immunoglobulins Module 6
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Transcript of Immunoglobulins Module 6
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Immunoglobulins
Prof. Dr: Sabah Abdel-Hady
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What are Immunoglobulins?
Immunoglobulins are -globulins that act asantibodies.
They mark pathogen for destruction by phagocytesand complement proteins
Synthesized to bind to one specific antigen
Immunoglobulins are glycoprotein in nature.
They are produced by plasma cells in response to an
immunogen.
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There are 5 classes
of immunoglobulins: IgG, IgA, IgM, IgD and IgE.
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The basic structure of Antibodies
Is the same for all classes:
Y-shaped
Composed of 4 polypeptide chains:
- 2 identical light chains (L)
- 2 identical heavy chains (H)
Linked by disulphide bonds.
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Both L and H chains have variable regions (VL & VH) amino
terminal NH2 part and constant regions (CL & CH) carboxy
terminal COOH part. The constant region has almost
constant amino acid sequence in
all Ig`s of the same class.
Some carbohydrate are
bounded to the constant regions
of the heavy chains.
Each Ig has 2 identical
antigen-binding sites.
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Fab region
Fc region
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Heavy chains
The VH region is the amino terminal , while CH region is thecarboxy terminal of H-chain.
The structure of CH region determines the class of Ig.
There are 5 types of heavy chains: ,, , , and those willdetermine the classes of Ig.
1. IgG - Gamma heavy chains ()
2. IgM - Mu heavy chains ()
3. IgA - Alpha heavy chains ()
4. IgD - Delta heavy chains ()
5. IgE - Epsilon heavy chains ()
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Immunoglobulin Subclasses
The classes of immunoglobulins can be divided into
subclasses based on small differences in the amino acid
sequences in the constant region of the heavy chains.
All immunoglobulins within a subclass have very similarheavy chain constant region amino acid sequences.
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Immunoglobulin Subclasses
1. IgG Subclasses
a) IgG1 - Gamma 1 heavy chains
b) IgG2 - Gamma 2 heavy chains
c) IgG3 - Gamma 3 heavy chains
d) IgG4 - Gamma 4 heavy chains
2. IgA Subclasses
a) IgA1 - Alpha 1 heavy chains
b) IgA2 - Alpha 2 heavy chains
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Light chains
Have lower molecular weight andlength than the H-chains.
The VL region is the amino terminal ,while the CL region is the carboxyterminal of L-chain.
CL region will determine the lightchains types: there are 2 types of lightchains: Kappa (k) and lambda ( ).
A given immunoglobulin moleculecontains two (k) or two ( ).
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The variable regions of Ig`s:
It has a variable amino acid
sequence and form the
antigen binding site of theimmunoglobulin.
Specific to Ag
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Digestion of an Ig`s
By the enzyme papain:
Occures at the hinge region, therefore it
produces two antigen binding
fragments (Fab) and one crystallizable
fragment (FC). By pepsin: Antigen binding fragment
(Fab)2 linked by disulphide bond.
(FC) crystalline fragment that will be
degraded to amino acids as digestionoccurs near the carboxy terminal half.
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IgG:
It is the most abundant immunoglobulin in serum. IgG is the major Ig in serum - 75% of serum Ig is IgG
It is the major Ig in extra vascular spaces
Structure:
Each IgG exists as a monomer consisting of two (k) or ()
light chains and two () heavy chains: (2L2). IgG1,IgG2,
IgG3 and IgG4 with 1 2 3 4 H chain.
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Secretory
IgA
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Structure:It exists as pentamer:
IgM
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IgE
IgE exists as a monomerconsisting of 2 (k) or () light chains
and 2 () heavy chains: (2L2).
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Which statement about the Fc part of
antibodies is not true?
A) It varies depending on the antigen class.B) It contains oligosaccharides.
C) It resembles of the L and of the H chains.
D) It can bind to antigen.
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How many heavy and light chains does a typical
immunoglobulin from the type G (IgG)contain?
A) one light and one heavy chain
B) two light and two heavy chains
C) two light and four heavy chains
D) four light and two heavy chains
E) four light and four heavy chains
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The antigen specificity of the antibody is located:
A) exclusively in the region of the heavy chains
B) within the C-terminal part of theimmunoglobulin chains
C) within the Fab-part of the immunoglobulins
D) within the Fc-part of the immunoglobulins
E) only in the variable part of the light chains