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8/4/2016
Antigen
• Substance when introduced into the
body stimulates the production of an
antibody
...
• May be proteins or polysaccharides
Types A
...
Incomplete antigen or hapten
• Usually non-protein substance and unable
to induce an immune response but become
immunogenic when linked to carrier
proteins
• It can react specifically with corresponding
antibody but has low molecular weight (less
than 10,000)
• eg, Blood group Glycoproteins, Drugs &
chemicals
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Properties of antigen
Foreignness
Size
Chemical nature
Susceptibilty to tissue enzymes
Antigenic specificity
Species specificity
Organ specificity
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8/4/2016
Antibodies: Structure And
Function
Antibodies
• A class of proteins referred to as the immunoglobulins
(Ig) with 4 polypeptides (2 heavy chains and 2 light
chains) held together by disulfide bridges to give them
their quaternary structure
• Most of the antibody structure is identical for all
antibodies with the “tips” variable that bind to the
epitope (exposed) region on the antigen surface
...
Structure of immunoglobulin
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8/4/2016
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IgG
IgA
IgM
IgD
IgE
Classification of Ig
contains γ-chain
contains α-chain
contains μ-chain
contains δ-chain
contains ε-chain
Antibody Classes And Biological Activities
IgG:
Most plentiful immunoglobulin of serum
Contains 75-80% of total Ig in circulation
MW : 150 Kda
Two heavy chains & two light chains
7S (sedimentation coefficient)
γ- chain (as heavy chain)
Half life : 23 days
I t triggers complement proteins and can cross
placenta Seen in secondary immune response
• Helps in opsonization
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IgM
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Macroglobulin
19S immunoglobulin
MW: 900 kDa
Five subunits each having 4 peptide chains (10 heavy chains &
10 light chains) are joined together by a J- chain polypeptide
μ chain (heavy chain)
Half life : 5 days
Helps in complement fixation
Are natural antibodies
Large molecule that initiates response by agglutinating
(clumping up) the antigens
...
• Released in secretions like Milk, saliva, tears,
mucus
...
They are in Very low serum concentration
...
Serum level increases in helminthic
infections
• Small amount, trigger the histamine release of
basophils and mast cells
...
8 days
They are found on surface of B-cells and initiate
the development of B-cells into plasma cells
...
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8/4/2016
Differences between immunoglobulins
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