Antibody Structure

Antibodies are a group of glycoprotein found in the serum and body fluids. They are gamma-globulins and therefore are known as immunoglobulin. Some are carried on the surface of B cells, where they act as receptors for specific antigens. Other antibodies are free in the blood or lymph. All antibodies have a similar overall structure with two light and two heavy chains. These are linked by both covalent (disulphide bridges) and non-covalent forces. They are made up of a series of domains of related amino acid sequence which possess a common secondary and tertiary structure. This conserved structure is found frequently in proteins involved in cell-cell interactions and is especially important in immunology.5 distinct classes of immunoglobulin molecules are recognized in most higher mammals which are IgG, IgA, IgM, IgD and IgE.They differ in size, charge, amino acid composition and carbohydrate content. They differ between classes and within each class. Electrophoretically, the immunoglobulin show a unique range of heterogeneity which extends from g to the a fractions of normal serum. Immunoglobulins are bifunctional molecules. One region of the molecule is concerned with binding to antigen while a different region mediates effector functions.Effector functions include binding of the immunoglobulin to host tissues, to various cells of the immune system, to some phagocytic cells, and to the first component (C1q) of classical complement system.