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# Antibody

an·ti·bod·y - AN-tih-bod-ee

## Definition

An antibody is a Y-shaped protein produced by specialized white blood cells called B lymphocytes (B cells) as part of the body's immune defense system. Each antibody is designed to recognize and bind to a specific foreign substance called an antigen - which could be a protein on the surface of a virus, bacterium, fungus, or other [pathogen](/glossary/pathogen). When an antibody locks onto its target antigen, it either neutralizes the threat directly or flags it for destruction by other [immune cells](/glossary/white-blood-cells).

Your immune system can produce millions of different antibodies, each precisely shaped to match a specific antigen. This remarkable specificity is the foundation of adaptive immunity - the ability of your immune system to learn from previous infections and mount faster, stronger responses upon re-exposure. This is also the principle behind vaccination: vaccines introduce harmless versions of [antigens](/glossary/antigen) that train your B cells to produce protective antibodies before you encounter the actual pathogen.

There are five main classes of antibodies (IgG, IgA, IgM, IgD, and IgE), each with distinct roles in immune defense. IgG is the most abundant and provides long-term immunity. IgA protects mucosal surfaces like the gut and airways. IgM is the first antibody produced during a new infection. IgE is involved in allergic reactions and defense against parasites.

## Also Known As

Immunoglobulin Ig 

## Key Facts

-   • The human body can produce over 10 billion different antibodies, each targeting a specific antigen. 
-   • The five classes of antibodies are IgG, IgA, IgM, IgD, and IgE - each with specialized functions. 
-   • Antibody tests (serology) can detect current or past infections, autoimmune conditions, and allergies. 
-   • Monoclonal antibodies are laboratory-made antibodies used as targeted treatments for cancer, autoimmune diseases, and other conditions. 
-   • Maternal antibodies (IgG) cross the placenta during pregnancy, providing temporary passive immunity to newborns. 

## How It Relates To Your Health

Antibody testing is widely used in clinical medicine for diagnosing infections (such as HIV, hepatitis, and COVID-19), detecting autoimmune disorders (where the body produces antibodies against its own tissues), identifying allergies (through IgE testing), and monitoring immune function. If you've had blood work that included an antibody panel, your doctor was evaluating how your immune system [has](/glossary/hyaluronic-acid) responded to specific threats.

Monoclonal antibody therapies represent one of the fastest-growing areas of modern medicine, with applications in treating cancers, rheumatoid arthritis, [Crohn's disease](/conditions/crohns-disease), [psoriasis](/conditions/psoriasis), and many other conditions where targeted immune modulation can reduce disease activity.

## Related Terms

[Antigen](/glossary/antigen)[T-Cells](/glossary/t-cells)[Autoimmune Response](/glossary/autoimmune-response)[Immune Response](/glossary/immune-response)[Allergen](/glossary/allergen)

## Sources

1.  [Antibodies](https://www.niaid.nih.gov/research/immune-cells) - National Institute of Allergy and Infectious Diseases (NIH)
2.  [Immunoglobulins](https://www.ncbi.nlm.nih.gov/books/NBK513460/) - StatPearls / PubMed
3.  [The Immune System](https://www.hopkinsmedicine.org/health/conditions-and-diseases/the-immune-system) - Johns Hopkins Medicine

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