Antibodies, also known as immunoglobulins, are glycoproteins produced by B-cells that bind to antigens with high specificity and affinity. There are two forms of antibodies: membrane-bound, which act as B-cell receptors, and secreted forms, which eliminate antigens through various mechanisms. Antibodies are classified into five types based on their constant region structure, each with specific roles in the immune response.

1. RAYHAN
13-BATCH
Q. What is antibody ?
Another name of anti-body is immunoglobulins . Anti-body is the glycoprotein which is produce by B-
cell and which are responsible to bind antigen with higher specifity and affinity. Anti-body is mainly
distrusted in body fluid and also present surface of some cell.
Q. Write down the mechanism of antibody production ?
Anti-body produce by B-cell which are two forms. They are-
1 . Membrane bond form
2 . Secreted form
Membrane bond form – These act as antigen binding site. The interaction of antigen with antibodies
initializes B-cell response and thus regulate the recognization phase of humoral immunity. It act as B-cell
receptor.
Secreted form- These are produced by the activated B-cell which are involved effector mechanism of
humoral immunity eliminate the antigen. They are present in biological fluid
Effector mechanism –
1) Neutralization 2) Activation of complement 3) Activation of macrophage 4) Opsonization of
antigen.

2. Q . Describe the structure of anti-body ?
VH = Variable of heavy chain. VL= variable of light chain. CH= constant heavy chain. =
immunoglobulin domain. –s-s- = Disulphide bond.
Every antibody have a symmetrical core structure composed of
1 ) Two identical light chain
2 ) two identical heavy chain
Light chain is so called because their molecular weight is lighter than heavy chain. The molecular weight
of light chain is about 23-24 KD and consist of about 200 amino acids. On the other hand , the molecular
weight of heavy chain is 55-70 KD and consist of about 400 amino acids. One light chain is attached to
one heavy chain by a disulphide bond and two heavy chain are attached to each other by disulphide bond.
Every antibody has two antigen binding sites because they have two identical variable region.

3. Q . Describe the classification of antibody ?
According to the structural difference of constant region immunoglobulin are five types. Each types of
antibody are called isotype. They are- 1) Ig M 2) IgG 3) IgA 4) Ig D 5) IgE
1 . IgM
IgM represent about 8-10% of the total serum of immunoglobulin pool.
FUNCTION OF Ig M:-
1 ) IT is the first antibody that are immunologically commited to lymphocyte and gives the response to an
antigen.
2 ) they can be bind with complement system.
3 ) It has antigen receptor on the surface of B-cells.
4 ) it is the only antibody made to certain carbohydrate antigen.
2 . IgG
IgG is the major immunoglobulin in human serum according from 70-80% of total immunoglobulin pool.
FUNCTION OF IgG:-
1 ) It is the main antibody in the secondary response .
2 ) It opsonizes bacteria , making them easier to phagocytize.
3 ) It fixes complement , which enhance bacterial killing .
4 ) It neutralizes bacterial toxins and virus.
3 . IgA
IgA is present in two forms – 1) In the serum and 2) In various body secrstions.
IgA represent 15-20% human serum. Secretory IgA can be further IgA1 , IgA2.
FUNCTION OF IgA:-
1 ) It protect mucosal surface from pathogenic microbes.
2 ) It does not fix complement
3) Secretory IgA prevents attachment of bacteria.

4. 4) Ig D
Ig D represent less than 1% of the total immunoglobulin pool but is present in large amount of the
membrane of many b-cells.
FUNCTION OF IgD:-
1 ) Its true function is recognization and binding of antigen.
2 ) It acts as a regulator for synthesis of other immunoglobulin.
3 ) the antigen receptor for native B-lymphocyte.
5) IgE
IgE is represent in trace amount in the normal serum 0.05 mg/dl accunting for only 0.004% of total serum
immunoglobulin.
FUNCTION OF IgE:-
1 ) IT does not fixe complement .
2 ) It is responsible for the alargic reaction.
3 ) It is the main host defense helminth injection.
4 ) It mediates immediate hypersensitivity by causing release of mediator from mast cell and basophils
upon exposure to antigen ( allergen).
Q . Difference between antigen and antibody?
Antigen Antibody
1 Antigen is protein or non-protein substance
which produce immune response in our body
Anti-body is the glycoprotein which is produce by B-cell
and which are responsible to bind antigen with higher
specifity and affinity.
2 There are three basic kinds of antigen. There are five basic kinds of antibody
3 Antigen are made of either protein or
polysaccharide .
Antibody is made of organic structure unit.
4 Antigen can be cell. Antibody are not cell.
5 Antigen causes disease Antibody cure it