Structure and Function of Antibodies

Antibodies, also known as immunoglobulins (Ig), are Y-shaped proteins produced by B cells in response to foreign substances called antigens. Structurally, antibodies are composed of four polypeptide chains: two identical heavy chains and two identical light chains, linked by disulfide bonds. This creates two main regions: the Fab (fragment antigen binding) region and the Fc (fragment crystallizable) region.

The Fab region is located on the two arms of the Y-shape and is responsible for antigen recognition. Each Fab region contains a variable domain that forms the antigen binding site, allowing the antibody to specifically bind to a unique epitope on the antigen. The variable regions are highly diverse, allowing the immune system to recognize a wide range of pathogens.

The Fc region is located in the stem of the antibody and mediates the interaction with the immune system. It binds to Fc receptors on immune cells (e.g. macrophages, NK cells) and activates immune responses such as phagocytosis or antibody-dependent cellular cytotoxicity (ADCC). The Fc region also plays a role in activating the complement system, thereby enhancing the destruction of pathogens.

Antibodies work by neutralizing pathogens, marking them for destruction (opsonization), and recruiting other immune components to attack infected cells. They are essential in protecting the body from infection and are also widely used in diagnostic, research, and therapeutic applications due to their high specificity for antigens.

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References

[1] Ryan Malonis et al., Chem Rev 2020 (10.1021/acs.chemrev.9b00472)

[2] Monica Fernandez-Quintero et al., 2023 (10.3390/antib12040067)