ANTIBODIES

ANTIBODIES ( IMMUNOGLOBULINS )

"Antibodies are large protein molecules produced by the body in response to an antigen and capable of reacting specifically with an antigen"

They are found in serum and some types are also found in body secretions.
STRUCTURE OF ANTIBODY

An antibody molecule is basically shaped like a Y. the molecule has two parts.

1. one part varies from antibody to anibody, depending on which antigen the antibody targets. The antigen attaches to the variable part.

2. the other part ( Constant part ) is one of five structures, which determines the antibody's class --- IgG , IgM , IgD , IgE or IgA. This part is the same within each class.



MAJOR TYPES ( CLASSES ) OF ANTIBODY

Antibodies are categorized into 5 classes, depending on the amino acids sequence in the C-Region and H-Region

1. IgA


2. IgD


3. IgE


4. IgG


5. IgM


1.IgA

• It occurs in two forms A) Serum IgA B) Secretory SIgA

• It occurs in mucus , tears and saliva

• Concentration in serum is very low

• But its concentration is significantly high in secretions

• Plays major role in defense against pathogens in the respiratory , gastrointestinal and genitourinary tracts.

• Copra antibodies are IgA antibodies Secreted into the intestinal tract.

• They provide protection against those food that otherwise would act as allergens.

• May be value in influenza, dysentery and pneumococal infection.
2.IgD

• Serves as a receptor for antigen on B Cells , usually along with IgM

• Can also play a role in immune suppression.
3.IgE

• Responsible for hay fever

• Rather than circulating in the blood it attaches itself to the mast cells and basophils.

• Triggered to release compounds such as histamine in the presence of the antigen to which the IgE binds

4.IgG

• Most Abundant Class Of Antibody in the serum.

• Accounts for 80-85% of the total serum antibodies.

• Can readily pass through the walls of the small blood vessels into extra cellular body spaces at the site of infection and reacts with antigen and stimulate chemotactic action.

• Capable of crossing the placenta and thus is responsible for conferring passive immunity.

• Largest half-life in serum and persists for 25 days

5.IgM

• Largest immunoglobulin molecule

• Found primarly in the circulation

• Effectively prevents microorganisms to disseminate in the body through blood stream.