OUTCOMES By the end of this session student should be able to know The structure of antibody Immunoglobulin classes Monoclonal antibodies VS polyclonal INTRODUCTION Antibodies are globulin proteins (immunoglobulins [Ig]) that react specifically with the antigen that stimulated their production. They make up about 20% of the protein in blood plasma. Blood contains three types of globulins, alpha, beta, gamma, Antibodies are gamma globulins. INTRODUCTION There are five classes of antibodies: 1. IgG, 2. IgM, 3. IgA, 4. IgD, 5. IgE Antibodies are subdivided into these five classes based on differences in their heavy chains. ROLE OF ANTIBODIES The most important functions of antibodies are to neutralize toxins and viruses, to opsonize microbes so they are more easily phagocytosed, to activate complement, and to prevent the attachment of microbes to mucosal surfaces. In addition to these functions, antibodies have a catalytic (enzymatic) capability Antibody Type IgA IgD IgE IgG IgM Function Found in saliva, tears, mucus, breast milk and intestinal fluid, IgA protects against ingested and inhaled pathogens. This antibody is found on the surface of your B cells. Though its exact function is unclear, experts think that IgD supports B cell maturation and activation. Found mainly in the skin, lungs and mucus membranes, IgE antibodies cause your mast cells (a type of white blood cell) to release histamine and other chemicals into your bloodstream. IgE antibodies are helpful for fighting off allergic reactions. This is the most common antibody, making up approximately 70% to 75% of all immunoglobulins in your body. It’s found mainly in blood and tissue fluids. IgG antibodies help protect your body from viral and bacterial infections. Found in your blood and lymph system, IgM antibodies act as the first line of defense against infections. They also play a large role in immune regulation. MONOCLONAL VS POLYCLONAL A. Polyclonal antibodies contain a heterologous mixture of IgGs against the whole antigen B. monoclonal antibodies are composed of a single IgG against one epitope. Polyclonal antibodies Monoclonal antibodies Refer to a mixture of immunoglobulin molecules that are secreted against a particular antigen. Refer to a homogenous population of antibodies that are produced by a single clone of plasma B cells. Produced by different clones of plasma B cells. Produced by the same clone of plasma B cells. A heterogeneous antibody population. A homogenous antibody population. Interact with different epitopes on the same antigen. Interact with a particular epitope on the antigen. STRUCTURE OF ANTIBODY Immunoglobulins are glycoproteins made up of 1. light (L) 2. heavy (H) polypeptide chains. The terms light and heavy refer to molecular weight STRUCTURE OF ANTIBODY The simplest antibody molecule has a Y shape consist of

1. ANTIBODIES
Dr. Rimsha Shahid
DVM (RVMP), Mphil. Pathology
Lecturer

3. OUTCOMES
By the end of this session student should be able to know
The structure of antibody
Immunoglobulin classes
Monoclonal antibodies VS polyclonal

4. INTRODUCTION
Antibodies are globulin proteins (immunoglobulins [Ig]) that react
specifically with the antigen that stimulated their production.
They make up about 20% of the protein in blood plasma. Blood
contains three types of globulins,
alpha,
beta,
gamma,
Antibodies are gamma globulins.

5. INTRODUCTION
There are five classes of antibodies:
1. IgG,
2. IgM,
3. IgA,
4. IgD,
5. IgE
Antibodies are subdivided into these five classes based on differences
in their heavy chains.

6. ROLE OF ANTIBODIES
The most important functions of antibodies are to
neutralize toxins and viruses,
to opsonize microbes
so they are more easily phagocytosed, to activate complement, and to
prevent the attachment of microbes to mucosal surfaces.
In addition to these functions, antibodies have a catalytic (enzymatic)
capability

7. Antibody
Type
Function
IgA
Found in saliva, tears, mucus, breast milk and intestinal fluid, IgA protects
against ingested and inhaled pathogens.
IgD
This antibody is found on the surface of your B cells. Though its exact
function is unclear, experts think that IgD supports B cell maturation and
activation.
IgE
Found mainly in the skin, lungs and mucus membranes, IgE antibodies
cause your mast cells (a type of white blood cell) to release histamine and
other chemicals into your bloodstream. IgE antibodies are helpful for
fighting off allergic reactions.
IgG
This is the most common antibody, making up approximately 70% to 75% of
all immunoglobulins in your body. It’s found mainly in blood and tissue
fluids. IgG antibodies help protect your body from viral and bacterial
infections.
IgM
Found in your blood and lymph system, IgM antibodies act as the first line of
defense against infections. They also play a large role in immune regulation.

8. MONOCLONAL VS POLYCLONAL
A. Polyclonal antibodies contain a heterologous mixture of IgGs
against the whole antigen
B. monoclonal antibodies are composed of a single IgG against one
epitope.

10. Polyclonal antibodies Monoclonal antibodies
Refer to a mixture of immunoglobulin
molecules that are secreted against a
particular antigen.
Refer to a homogenous population of
antibodies that are produced by a single
clone of plasma B cells.
Produced by different clones of plasma B
cells.
Produced by the same clone of plasma B
cells.
A heterogeneous antibody population. A homogenous antibody population.
Interact with different epitopes on the same
antigen.
Interact with a particular epitope on the
antigen.

11. STRUCTURE OF ANTIBODY
Immunoglobulins are glycoproteins made up of
1. light (L)
2. heavy (H) polypeptide chains.
The terms light and heavy refer to molecular weight

12. STRUCTURE OF ANTIBODY
The simplest antibody molecule has a Y shape
consists of four polypeptide chains:
1. two H chains
2. two L chains
The four chains are linked by disulfide bonds.
An individual antibody molecule always consists of identical H chains and
identical L chains.
L and H chains are subdivided into
1. variable
2. constant regions.

13. STRUCTURE OF ANTIBODY
The variable regions of both L and H chains have three extremely
variable amino acid sequences at the amino-terminal end that form
the antigen-binding site

16. HEAVY CHAINS
Five types of heavy chains are present
They are;
1)alpha(α)
2)gamma(γ)
3)delta(Δ)
4)epsilon
5)mu(μ)

17. LIGHT CHAINS
Two types of light chains are present
They are;
1)kappa
2)lambda
All antibodies have one of the two kinds of light chains

18. 1. IgG:
Molecular weight: 150,000 Da
IgG is the most abundant class of Immunoglobulin in serum and constitute
of about 80% of total serum immunoglobulin.
IgG molecule consists of two gamma (γ) heavy chains and two kappa (k) or
two lambda (λ) light chains.
There are four sub class of IgG ( IgG1, IgG2, IgG3 and IgG4) on the basis of
decreasing serum concentration.
It has longest half-life among other antibodies. Half-life is about 23 days.
IgG is the only antibody that can cross placenta. It cross placenta and
provide immunity to fetus upto 6 month of age. The immunity is known as
natural passive immunity.
It can also activate complement.

19. 1. IgG:
Biological functions:
IgG is the major antibody produced in secondary immune response.
Ig, IgG3 and IgG4 readily cross the placenta and play important role
in protecting the fetus.
IgG3 is the most effective complement activator followed by IgG1 and
IgG2. IgG4 is not able to activate complement at all.
IgG1 and IgG3 binds with high affinity to Fc receptor on phagocytic
cell and thus mediate opsonization.
IgG helps in bacterial immobilization.
IgG neutralize toxin and viruses

21. 2. IgM:
Molecular weight: 900,000 Da
IgM accounts for 5-10% of total serum Immunoglobulin
IgM is secreted by plasma cell and it exists in pentameric form in which five
IgM mononers are linked together by disulphide bond (J-chain).
Due to large size, IgM is also known as millionare molecule.
There are 10 antigen binding site (Fab) in pentameric IgM molecule but it
cannot bind to 10 complete antigen due to steric hindrance.
It is the major antibody produced during primary immune response.

22. 2. IgM:
Biological functions:
IgM is the first antibody produced in primary immune response and it
is also the first Ig produced by neonate.
IgM has higher valency (antigen binding site) due to its pentameric
form.
IgM is more efficient than IgG in complement activation.
IgM plays important accessory role as secretory immunoglobulin due
to J-chain.

24. 3. IgA:
Molecular weight: 320,000 Da
IgA constitute 10-15% of total serum immunoglobulin.
It is the predominant Immunoglobulin in external secretions such as breast
milk, saliva, tears and mucus of bronchial, genitourinary and digestive tracts.
IgA primarily exists as monomeric form but dimeric, trimeric and some
tetrameric form are also present.
IgA in blood occurs in monomeric form whereas those in body secretion
occurs in dimeric or multimeric forms.
IgA can cross epithelial layer and enter into body secretion. The process of
crossing epithelial layer by IgA is known as transcytosis.
There are two sub-class of IgA ie. IgA1 and IgA2.

25. 3. IgA:
Biological functions;
IgA can cross the epithelial layer and enter into body secretion and
provides local immunity in GI tracts, respiratory tract, genital tract etc
In body secretion IgA neutralize viruses and prevent attachment on
host surface.

28. 4. IgD:
Molecular weight: 180,000 Da
IgD is present in extremely low concentration and it constitute 0.2%
of total serum immunoglobulin.
IgD together with IgM is the major membrane bound immunoglobulin
expressed on mature B-cell.
There are two sub-classes of IgD (IgD1 and IgD2)
IgD plays important role in maturation and proliferation of B-cell.

30. 5. IgE:
Molecular weight: 200,000 Da
IgE accounts for 0.3% of total serum Immunoglobulin.
IgE is also known as reagenic antibody due to its involvement in
allergic reaction. IgE mediate immediate hypersensitivity reaction and
responsible for symptoms like hey fever, asthma, anaphylactic
shocks, etc.
Fc region of IgE binds on blood basophils and tissue mast cells. The
cross reaction with antigen to Fc region bound IgE causes
degranulation of mast cell and basophils releasing histamine.
Histamine is responsible for symptoms of allergy.

31. 5. IgE:
Biological functions;
IgE provides immunity against parasite by Antibody dependent cell
mediated cytotoxicity (ADCC).
Level of IgE antibody in blood of normal individual is very low and its
level increases during parasitic infection and in allergic reactions.