Description: Antibodies are soluble immunoglobulins (Ig) produced by plasma cells in response to an immunogen and are critically involved in the immune response. Each immunoglobulin actually binds to a specific antigenic determinant (epitope).
All immunoglobulins have a four chain structure as their basic unit. They are composed of two identical light chains (lambda or kappa; 23kD) and two identical heavy chains (alpha, delta, gamma, epsilon or mu; 50-70kD) connected by disulfide bonds.
Based on the differences in the amino acid sequences in the constant region (Fc-part) of the heavy chains the immunoglobulins can be divided into five different classes: IgG, IgM, IgA, IgD and IgE. IgGs can additionally be divided into 4 subclasses based on the number of disulfide bonds and length of the hinge region.
If different immunoglobulin classes or isotypes recognize an antigen at the same epitope, they still differ in the way the immune system reacts to the antigen. The specific Fc-part will promote a specific effector function of the immune system to the antigen.The isotype of an antibody determines ist distribution to the different compartments of the body in which their particular effector functions are appropriate.
Changes in the relative abundance of the different isotypes usually indicate immunological disorders or disease states. Isotype profiling of serum/plasma samples may help to identify or study selective antibody deficiency conditions, other immune deficiency diseases or allergic disease.
On the other hand immunoglobulin isotyping is an important application for analyzing and monitoring hybridomas during monoclonal antibody production. Different isotypes have different chemical and biological properties. They differ in their solubility and electrophoretic properties, in their susceptibility to cleavage enzymes and in their reactivity with protein A, which is important information to chose the right purification method.