by Luana

Created on: April 17, 2010

        Definition of an Antibody.

Antibodies are proteins called immuniglobulins which are produced, by B lymphocytes  in response to an antigen. Antibodies are specific for each type of antigen and will attach to the antigen, neutralising/ destroying the antigen.  Most antibodies are protective but inapproprate formation of antibodies can lead to severe disease processes. 

An antigen is a toxin produced  or cell  such as bacteria and virus that is recognised as a foreign body by the immune system sending a message to stimulate an attack  by producing antibodies in order to get rid of this foreign body.

       Structure and Classes of Antibody. 

Each antibody consisits of  4 polypeptide chains. There are 2 heavy chains that form a 'Y' shape and 2 light chains that are attached to the outer (lateral) side of the arms (i.e the V portion) of the Y.

Each antibody has  two  main regions called the Variable and the Constant region. The Variable region has the site that binds to the antigen and the Constant region determines the mechanism of destroying the foreign body/antigen. The structure of the Constant region divides antibodies into Five Classes called  IgA, IgD,IgE,IgG and IgM. because the 'Y' shape can join at the constant regions (l portion) and function as momomers (single Y), dimers (2Y), trimers(3Y), tetramers(4Y) and pentamers(5Y)  this then determines the size and shape.

       Functions of the 5 Classes of Antibodies/Immunoglobulins 

•IgA is found in the bloodstream and  under the mucosal surfaces of areas with direct contact to the external environment such as nasal mucosa, digestive tract including mouth, vaginal mucosa,ears and secretions such as,tears,saliva,breast milk and accounts for 15%-20% of antibodies in the body.  These antibodies can function as 2Y,3Y,4Y and 5Y.

 IgD is found in blood but in small amounts. Usually together with IgM and is about 1% of antibodies. Functions as single Y only and is thought to help the B cells decide which type of Immunoglobulin to produce for that specific antigen.

• IgE is present in minute amounts in the blood about .001% but in large quantities attached to

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