Antibody is very important in human haematology and blood banking

1. Antibodies
DR.SHAHIDA BALOCH

2. WHAT ARE ANTIBODIES? Antibodies, also known as
immunoglobulins, are Y-shaped proteins
that are produced by the immune
system to help stop intruders from
harming the body. When an intruder
enters the body, the immune system
springs into action. These invaders,
which are called antigens, can be
viruses, bacteria, or other chemicals.
When an antigen is found in the body,
the immune system will create
antibodies to mark the antigen for the
body to destroy.

3. Basic structure of Antibody
IMMUNOGLOBULIN DOMAINS
Antibody is composed of two identical heavy polypeptide chains and
two identical light chains, bonded via interchain disulphide[s-s]
linkages
Each chain is composed of structural domains called
Immunoglobulin domains
These domains contains about 70-110 aminoacids

4. Function
The antibodies act sort of like the immune system's scouts. They find
antigens, stick to them, and identify for the immune system the
exact type of antigen so that it can be destroyed. Each antibody is
made for one and only one antigen, and it's fitted with special
receptors that will only bind to that antigen. For instance, a specific
antibody is created to help destroy the chickenpox virus. Only that
particular antibody will attack a chickenpox virus.

5. STRUCTURE
All antibodies share a basic structure
Antibodies are heavy globular plasma proteins[or]glycoproteins
The attached glycans are critically important to the structure and function of
the antibody
Each antibody is heterodiamer with a molecular weight of approximately 150KD

6. How Antibodies Fight Antigens
When an antigen tries to enter the body? When it does, the immune
system is triggered. Chemical signals are sent to alert all the different
parts of the immune system into action.
First, the virus is met by a type of cell called B cells. The B cells are
responsible for creating antibodies to match the antigen. Remember,
each type of antibody matches to only one antigen. After the B cells
have created their antibodies, the antibodies stick to the virus,
marking it for the next round of attack. T cells are then ordered to
attack the antigen that the antibodies have marked for it.
After the antigen has been destroyed, the cleanup crew comes
along. A wave of phagocytes, large cells that can consume foreign
matter, eats the remains of the infection.

7. Immunizations
After an infection is defeated, the antibodies still remain in the body.
They are left there to wait in case that particular antigen returns. For
example, after a person gets chickenpox, the antibody that was
created by the immune system to get rid of the chickenpox will
remain in the body. The next time the chickenpox virus tries to
invade the patient, the antibody will be ready. It will instantly attach
to the virus, calling the T cells and phagocytes much quicker, and
stopping the infection much earlier.
Immunizations take advantage of the fact that antibodies remain in
the body after an infection is eradicated. Most immunizations consist
of a weak or diluted form of an antigen - not enough of the antigen
to make the patient sick, but just enough to trigger the creation of
antibodies. This way, the body can instantly attack any form of the
infection it encounters, stopping the infections before they begin.

8. Types of Antibodies
There are 5 types of antibodies. Each type found in a different part of
the body has different set of duties.
Ig= Immunoglobulin
High molecular glycoprotein

9. Types Of Antibodies

10. DIFFERENT CLASSES OF
ANTIBODIES
There are five classes of antibodies are present
They are;
1)IgG
2)IgM
3)IgA
4)IgD
5)IgE
The antibody classes are named as correspond to their heavy chain
types

11. Ig Major Functions
Ig G
Main antibody in the secondary response. Opsonizes
bacteria, making them easier to phagocytize. Fixes
complement, which enhances bacterial killing. Neutralizes
bacterial toxins and viruses. Crosses the placenta.
Ig A Secretory IgA prevents attachment of bacteria and viruses
to mucous membranes Does not fix complement.
Ig M Produced in the primary response to an antigen. Fixes
complement. Does not cross the placenta. Antigen receptor
on the surface of B cells.
Ig D Uncertain. Found on the surface of many B cells as well as
in serum.
Ig E
Mediates immediate hypersensitivity by causing release of
mediators from mast cells and basophils upon exposure to
antigen (allergen). Defends against worm infections by
causing release of enzymes from eosinophils. Does not fix
complement. Main host defense against helminth
infections.

12. Naive B cells which never exposed to
antigen on encountering them
differentiate into Memory Cells and
plasma cells. Memory B cells recognize
the antigens epitopes and have longer
life,while plasma cells are effector cells
they secrete the antibodies and have
shorter life.
Plasma cells and Memory B cells

13. B lymphocytes mature within the bone marrow.
Mature, naive B cells then migrate to peripheral lymph nodes, where they await B cell
activation mediated by dendritic cells and CD4+ effector cells.
Once in the circulation, they express a single, unique immunoglobulin (IgM).
When a B cell encounters an antigen that matches its antibody, it proliferates rapidly and
differentiates into memory B cells and effector B cells (Plasma cells).
Memory B cells have a longer life span and express membrane-bound antibody.
Plasma cells produce soluble antibody. Although they live for only a few days, they secrete
enormous amounts of antibody, estimated at perhaps 2000 molecules per second.

14. Immune Response
Primary response. After first injection of the antigen
there is a long lag phase of several days before
antibody appears.
Secondary immune response. If the same host is
subsequently exposed to the same antigen, then the
secondary immune response is usually mote
pronouced and occur more rapidly. Because of the
availability of specific memory cells, an increased
number of effector cells are produced.
The antibody formed in primary response is
predominantly IgM and in secondary response IgG.

15. Immunoglobulin
1)IgG
They makes up approximately 80% of the serum antibodies
They has a half-life of 7-23 days
 IgG is a monomer and has 2-epitope binding sites
 This is the only class of antibodies that can cross the placenta and enter the fetal circulation
Functions
 Immunity to new born
 Neutralization of Toxins
 IgG3 binds to Fc receptor by Phagocytosis

16. Immunoglobulin
 2)IgM
 They makes up approximately 13% of the serum antibodies
 They has a half-life of about 5 days
 Most of the IgM are pentamer and has 10 - epitope binding sites, some are monomer
 It is the first immunoglobulin class produced in a primary response to antigen
 functions
 Activation of classical pathway
 Defence against multivalent antigens
 Act as Opsonin

17. Immunoglobulin
IgA
 They makes up approximately 6% of the serum antibodies
 They has a half-life of approximately 5 days
 IgA is a dimer and has 4-epitope binding sites
 They found mainly in body secretions such as saliva,mucous,tears,colostrum
and milk
 Functions
 It as a Secretory antibody
 Effective against virus that causing Influnza
 Production to Infant gut

18. Immunoglobulin
 4)IgD
 They makes up approximately 0.2% of the serum antibodies
 IgD is a monomer and has 2-epitope binding sites
 This class antibodies are found on the surface of B-lymphocytes
Function
 B cell activation.
 Act a receptor for antigen binding

19. Immunoglobulin
5)IgE
 It was discovered by KandT Ishizaka
 It is very low concentration in blood(17-450ng/ml)
 It contain small percentage of Lympocytes
Functions
 Responsible for Immediate hypersensitivity
 Binds to Fc receptor on basophils and mast cells
 Release of substance like histamine ,vasoactive mediators