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Introduction to Monoclonal Antibodies (mAbs)

Antibodies are proteins that when synthesized in vivo, typically by specific white blood cells in the bone marrow, are used by the body's immune system to target and remove any pathogenic agents (such as bacteria or viruses) that have been detected. An antigen is a specific molecule of the harmful pathogen that induces this immune response.

Figure 1: Monoclonal antibodies (mAbs)

Antibodies are a part of a family of globular proteins called immunoglobulins (Ig). The most common immunoglobulin class used for biopharmaceutical monoclonal antibodies (mAbs) is immunoglobulin G (IgG); notable by their characteristic Y-shape. The area that recognizes the pathogen as harmful is the antigen-binding site in the variable regions, located at the two tips of the Y 'arms'.


Figure 2: Structural features of a monoclonal antibody (mAb)

The whole Y 'arms' section of the mAb is referred to as the fragment antigen binding (Fab) portion of the structure. Each antibody Fab portion contains a section of both constant and variable heavy chain, as well as the constant and variable regions of the light chains. The fragment crystallizable (Fc) region is comprised of the remaining, identical, heavy chain constant regions. It is this lower section of an antibody (the 'stem' of the Y) that is responsible for interacting with other proteins and cell surface receptors to trigger an immune response.

The characteristic Y format of the antibody is held in place by disulfide bon1ds; responsible for linking the two sections of the heavy chains, and also the light chain to the heavy chain. These disulfide bonds are crucial for maintaining the antibody structure, and therefore biological function. It is essential that these disulfide linkages are correctly formed and do not become modified as they play a vital role in determining the structural confirmation of the antibodies; specifically the position of the Fab and Fc sections relative to each other, due to the disulfide bonds within the hinge region. An antibody with an unusual confirmation will not be able to interact in the necessary manner to perform its required function.

There are multiple additional disulfide bonds located at various locations across IgG surfaces that also play a role in deciding antibody structure and function.

 
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