Immunoglobulins Module 6

8/9/2019 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

Immunoglobulins Module 6

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