antigen
Americannoun
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Immunology. any substance, as a protein, carbohydrate, etc., that, on entering the body, can stimulate an immune response and combine with a specific antibody or T cell receptor having a matching molecular structure.
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Pharmacology. any commercial substance, usually synthetic, that stimulates the production of antibodies when injected or absorbed into animal tissues.
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antigens of a particular type collectively.
noun
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A substance that stimulates the production of an antibody when introduced into the body. Antigens include toxins, bacteria, viruses, and other foreign substances.
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Compare antibody See Note at blood type
Usage
What does antigen mean? An antigen is a substance that causes an immune response in the body—specifically, an antigen causes the body to produce antibodies. Antigens are things like viruses, bacteria, toxins, cancer cells, and other foreign substances, like the cells of a transplanted organ.An antibody is a protein produced by some cells as part of the immune system’s defenses. Antibodies attach to antigens and make them harmless or help the body to destroy them.Antigens are studied in fields like immunology, virology, and pharmacology. Most vaccines contain forms of antigens that trigger the body to produce specific antibodies to fight that antigen.
Other Word Forms
- antigenic adjective
- antigenically adverb
- antigenicity noun
Etymology
Origin of antigen
First recorded in 1905–10; anti(body) + -gen
Compare meaning
How does antigen compare to similar and commonly confused words? Explore the most common comparisons:
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
In a Phase 1 trial, 14 of 17 patients showed at least a 50% reduction in prostate-specific antigen, or PSA, a protein that indicates the presence of prostate cancer at elevated levels.
From Barron's • Feb. 24, 2026
It also includes a harmless antigen, an egg protein known as ovalbumin or OVA, which draws T cells into the lungs and helps sustain the boosted innate response for weeks to months.
From Science Daily • Feb. 23, 2026
This method of antigen design and adenovirus delivery closely mirrors the approach used for the COVID-19 nasal vaccine.
From Science Daily • Feb. 4, 2026
But advanced prostate cancer has increased in recent years as fewer men receive prostate-specific antigen tests.
From The Wall Street Journal • Jan. 14, 2026
When the connection is made, and a particular lymphocyte with a particular receptor is brought into the presence of the particular antigen, one of the greatest small spectacles in nature occurs.
From "The Lives of a Cell" by Lewis Thomas
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
