2. Introduction
Immunoglobulin are immunologically active serum protein formed in response to an
antigen and react specifically with that antigen.
They are briefly represented as (Ig). They are commonly called antibodies (Ab).
Immunoglobulin are immunological missles produced by the body. they are found in
the serum, body fluids and tissues. they are produced by vertebrates only. they are
synthesized by lymphocytes and plasma cells.
Rodney Porter (1962) -proposed the basic structure of immunoglobulin.
immunoglobulin is a glycoprotein.
it is an Y shaped or T shaped molecule. it is made up of four polypeptide chains.
May or may not react with antigen. when an immunoglobulin react with an antigen,
it is called an antibody. when is it does not react with an antigen it is simply called
immunoglobulin. All antibodies are immunoglobulin but all immunoglobulin may
not be antibodies.
3. structure of immunoglobulin
Antibody / immunoglobulin molecules are
glycoproteins composed of one or more units, each
containing four polypeptide chains-
Two chain are longer ,they are called identical
heavy chains (H) andTwo chain are short ,they are
called identical light chains (L).
Each light chain is made up of 214 amino acid and
each heavy chain is made up of 450 to 700 amino
acid.
They are two type of light chains - Kappa and
Lambda.
They are Five type of Heavy chains- Gamma, Alpha,
Mu, Delta & Epsilon.
4. One end of each chain is called amino-terminal end or N- terminal end and the other
end is called carboxy terminal end or c- terminal end. they have each has a central
flexible reason called hinge.
The four chain are interconnected by interchain disulfide bonds. The two heavy chain
are linked by 1to 13 interchain disulfide Bond. each light chain is linked to a heavy
chain by single interchain disulfide Bond.
the light chain has 2 intrachain disulfide Bonds and the heavy chain has 4 intrachain
disulfide Bonds.
The immunoglobulin consists of two region, namely a variable region ( V-region) and
a constant region (C- region).
5. Based on the functional aspect, two region can be recognized in the
immunoglobulin. They are Fab fragment or antigen binding fragment and FC
fragment or crystallisable fragment. The Fab is located at the extremely of the two
limbs of Y . The Fab fragment reacts with the antigenic determinants and its N-
terminal binds with the antigen.
Each L chain consists of one variable domain, VL, and one constant domain, CL. The
H chains consist of a variable domain, VH, and three constant domains CH1, CH2
and CH3.
6. Classes of immunoglobulin
The five primary classes of immunoglobulin are IgG, IgM, IgA, IgD and IgE.
They are named based on the nature of heavy chains they have.
Immunoglobulin Molecular weight ranges from 150000 to 950000.
The half life varies from 2 to 25 days.
S.No. Name of Ig Nature of Heavy chains
1 IgG- Immunoglobulin G Gamma
2 IgM – Immunoglobulin M Mu
3 IgA- Immunoglobulin A Alpha
4 IgD- Immunoglobulin D Delta
5 IgE- Immunoglobulin E Epsilon
7. Class- 1. IgG
• IgG is a immunoglobulin G.
• It is an antibody.
• It is a glycoprotein.
• It is Y shaped.
• It is a stable, 4 polypeptide chained molecular formed of 2 light Chains and 2
heavy chain of gamma type.
• light chain consists single constant domain(CL)and a single variable domain
(VL).
• IgG has half life of 25 days.
Properties of IgG:
Molecular weight: 150,000
H-chain type (MW): gamma (53,000)
Serum concentration: 10 to 16 mg/mL
Percent of total immunoglobulin: 75%
Glycosylation (by weight): 3%
Distribution: intra- and extravascular
Function: secondary response,
IgG is the only class of Ig that can cross the placenta in humans, and it is largely responsible
for protection of the newborn during the first months of life, IgG is the principle antibody
used in immunological research and clinical diagnostics..
8. Class- 2. IgM
• IgM is an antibody.
• It is Y shaped.
• It is often referred as the “Macroglobulin” bacause of its high mol.weight.
• It is the largest of the immunoglobulin.
• They are polymers of usually 5 molecules (pentamers structure) each with 4
polypeptide chains.
• Monomers of serum IgM are bound together by disulfide bonds and a joining
(J) chain.
• The serum level of IgM is very low.
• IgM has half life of 5 days.
Properties of IgM:
Molecular weight: 950,000
H-chain type (MW): mu (65,000)
Serum concentration: 0.5 to 2 mg/mL
Percent of total immunoglobulin: 10%
Glycosylation (by weight): 12%
Distribution: mostly intravascular
Function: It is first antibody to appear in the primary immune.
9. Class- 3. IgA
• IgA is an antibody.
• IgA is found in serum.
• It is a glycoprotein.
• It is Y shaped.
• It has two types, namely serum IgA and Secretory IgA.
• It has 4 polypeptide chains- 2 light Chains and 2 heavy.
• It occurs as a dimer formed of two molecules of IgA linked by a Secretory
component (SC) or Secretory piece and a J chain (joining chain).
• Both Secretory component or Secretory piece protein.
• IgA has half life of 6-8 days.
Properties of IgA:
Molecular weight: 320,000 (secretory)
H-chain type (MW): alpha (55,000)
Serum concentration: 1 to 4 mg/mL
Percent of total immunoglobulin: 15%
Glycosylation (by weight): 10%
Distribution: intravascular and secretions
Function: protect mucus membranes/colostrum protects the baby from intestinal
infection/immunity against tapeworms.
10. Class- 4. IgD
• IgD has a typical immunoglobulin structure.
• IgD is limits to the blood serum.
• IgD has a half life of 2-3 days.
Properties of IgD:
Molecular weight: 180,000
H-chain type (MW): delta (70,000)
Serum concentration: 0 to 0.4 mg/mL
Percent of total immunoglobulin: 0.2%
Glycosylation (by weight): 13%
Distribution: surface of B-lymphocytes.
Function: unknown
Class- 5. IgE
• IgE has a typical immunoglobulin structure.
• IgE is known as skin sensitizing antibody.
• IgE has half life of 2-3 days.
Properties of IgE:
Molecular weight: 200,000
H-chain type (MW): epsilon (73,000)
Serum concentration: 10 to 400 ng/mL
Percent of total immunoglobulin: 0.002%
Glycosylation (by weight): 12%
Distribution: basophils and mast cells in saliva and nasal secretions.
Function: protect against parasites.
11. Function of immunoglobulin
The main function of the immunoglobulin is protection of the body against
the invading microorganisms. The protective role in carried out in the
following Ways-
1 Agglutination of antigens.
2 Precipitation of antigens.
3 Neutralization of antigens.
4 Lysis of the antigens.
5 Opsonisation.
6 Tissue fixation.
7 Phagocytosis.
8 Chemotaxis.
9 Activation of mast cell and basophils
