Antibody (Ab)

Antibody (Ab)

Definition

An antibody, also known as an immunoglobulin (Ig), is a large, Y-shaped protein produced by the immune system in response to the presence of foreign substances called antigens. Antibodies play a critical role in identifying and neutralizing pathogens such as bacteria and viruses.

Structure

Antibodies are composed of four polypeptide chains: two identical heavy chains and two identical light chains, connected by disulfide bonds. The structure resembles a “Y,” where the tips of the “Y” contain regions known as paratopes that specifically bind to unique portions of an antigen called epitopes.

Function

• Recognition: Antibodies recognize and bind to specific antigens, marking them for destruction by other immune cells.
• Neutralization: They can neutralize toxins or pathogens directly by blocking their ability to interact with host cells.
• Activation of Immune Responses: Antibody binding can trigger additional immune responses, such as activating the complement system or facilitating phagocytosis by immune cells.

Types of Antibodies

There are five main classes of antibodies in humans, each with distinct functions:

1. IgG: The most abundant antibody in serum, providing the majority of antibody-based immunity against invading pathogens.
2. IgM: The first antibody produced in response to an infection; it is effective in forming complexes with antigens.
3. IgA: Found in mucosal areas, such as the gut and respiratory tract, as well as in secretions like saliva and breast milk.
4. IgE: Involved in allergic reactions and responses to parasitic infections.
5. IgD: Functions mainly as a receptor on B cells that have not been exposed to antigens.

Production

Antibodies (Ab) are produced by specialized white blood cells called B lymphocytes (B cells). Upon encountering an antigen, B cells are activated to proliferate and differentiate into plasma cells, which secrete large quantities of antibodies into the bloodstream.

Clinical Significance

Antibodies are crucial for diagnosing diseases, developing vaccines, and treating various conditions through therapies such as monoclonal antibodies. They can also be involved in autoimmune disorders when the immune system mistakenly targets the body’s own tissues.

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References

1. National Human Genome Research Institute. (n.d.). Antibody. Retrieved from Genome.gov DOI: 10.1016/j.cell.2013.05.029.
2. Wikipedia. (2023). Antibody. Retrieved from Wikipedia DOI: 10.1016/j.cell.2013.05.029.
3. Cleveland Clinic. (n.d.). Antibodies: Definition, Types & Function. Retrieved from Cleveland Clinic DOI: 10.1016/j.jpsychores.2009.02.001.
4. Britannica. (2023). Antibody | Definition, Structure, Function, & Types. Retrieved from Britannica DOI: 10.1016/j.cell.2013.05.029.
5. StatPearls – NCBI Bookshelf (2022). Physiology, Antibody. Retrieved from NCBI DOI: 10.1007/s12053-017-9571-5.