In this article we will discuss about the structure of antibody with the help of suitable diagram. Also learn about the production of monoclonal antibodies.
The chemical substance produced by the body against the antigen is called antibody. Antibodies belong to a group referred to as gamma globulins and are called immuno globulins. They have molecular weight between 160,000 and 9, 70, 000. An antibody molecule is shaped like the letter ‘Y’ and has two identical antigen binding sites that precisely fit the shape of a particular antigen (Fig. 7).
Structurally it is made of two heavy chains and two light chains. Each chain has a variable region and a constant region. The variable region is responsible for the variations in the kinds of antibodies. The variable region varies greatly among different antibodies. This variable region, composed of 110-130 amino acids, gives the antibody its specificity for binding antigen.
Antibodies are of five classes – IgG, IgA, IgM, IgD and IgE. Ig stands for immunoglobulins. IgG constitutes to about 75% of the total antibodies. IgE is involved in allergy and IgM is formed during the primary response. Human body can produce nearly 100 million antibodies.
Antigen-antibody reactions (Fig. 8) are highly specific and both fit into each other like a lock and key. Because an antibody fits precisely with an antigen, an antibody that binds to one antigen cannot bind to another antigen.
Antibody can inactivate the invading agent in one of the following ways:
a. Agglutination:
Antibodies make antigens clump together. This is called agglutination; the clumped antigens are not active. Macrophages engulf and destroy the clumped antigens
b. Precipitation:
The antigen-antibody complex become large and insoluble and precipitates.
c. Neutralisation:
The antibody covers the toxic site of the antigen.
d. Lysis:
The antibody attaches to the membranes of the cellular invading agent and causes rupture of the cell.
The body has a characteristic property of distinguishing its own antigen (‘self’) from the foreign antigen (‘non-self’). Therefore, normally no antibody is produced against the body.
Monoclonal Antibodies:
Mice are immunized with an antigen, and B cells isolated from the blood (Fig. 9). These cells are fused with cancer cells that are capable of growing in culture. The hybrid cells produced are known as hybridomas, which are capable of producing monoclonal antibodies (Fig. 9). Antibodies produced from these ‘hybridomas’ are very useful in biology and medicine.
The production of antibodies from the first exposure to an antigen is known as the primary immune response. The primary immune response thus occurs when the immune system first encounters a new pathogen.
A few of the lymphoblasts however remain as the memory cells and help in fighting an infection of antigen that may enter for the second time. This is called secondary response. The time taken to initiate a secondary response is faster than the primary response because of the presence of memory cells. A secondary immune response is more powerful than the primary response, producing antibodies very quickly that the disease never gets a chance to develop.