Antibodies

Antibodies are proteins belonging to a group of glycoproteins which are synthesized in the body in response to immune reaction produced by foreign proteins or toxins,called antigens. Antibodies are referred to as immunoglobulins (Ig) , each with a specific antigenic determinant with which it combines. These are synthesized by a special process in spleen and lymphatic cells. According to a modest estimate, an individual can synthesize as many as 106 types of antibodies which can be distinguished by radioimmunoassay technique.

Five classes of immunoglobulins which have different functional roles in the body have been identified in the human plasma. These are :IgG IgA, IgM , IgD and IgE. An antibody contains two kinds of polypeptide chains, heavy and light, and can bind two antigen molecules simultaneously. One pair of identical heavy chains is combined with another pair of identical light chains in a way that each arm of the molecule contains light chain bound to an equalsized heavy chain. The arms have the amino terminal of the amino acid sequence. The stem of the molecule is composed of the remaining carboxyl terminal portions of the heavy chains. The chains are stabilized by disulphide bonds.