Antigen | Definition, Function, Types, & Facts - Encyclopedia Britannica

🤑 Explore Britannica's Newest Newsletter: Money Matters Learn More Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos antigen Introduction References & Edit History Related Topics Images & Videos Quizzes A Visit with the Word Doctor: Medical Vocabulary Quiz All About Biology Quiz 44 Questions from Britannica’s Most Popular Health and Medicine Quizzes Contents Health & Medicine Conditions & Diseases Trauma CITE verifiedCite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/science/antigen Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback

Our editors will review what you’ve submitted and determine whether to revise the article.

External Websites

• National Center for Biotechnology Information - Blood group antigens are surface markers on the red blood cell membrane
• Healthline - What�s the Difference Between Antigens and Antibodies?
• Biology LibreTexts - Antigens
• PNAS - Physical extraction of antigen and information
• CellPress - Current Biology - Antigen presentation
• Demo Pressbooks Network - Boundless Anatomy and Physiology - Antigens
• Mustansiriyah University - Antigen and antibody (PDF)
• Cleveland Clinic - Antigen

Britannica Websites Articles from Britannica Encyclopedias for elementary and high school students.

• antigen - Student Encyclopedia (Ages 11 and up)

antigen biochemistry Ask Anything Homework Help Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Feb. 18, 2026 •History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

antigen, substance that is capable of stimulating an immune response, specifically activating lymphocytes, which are the body’s infection-fighting white blood cells. In general, two main divisions of antigens are recognized: foreign antigens (or heteroantigens) and autoantigens (or self-antigens). Foreign antigens originate from outside the body. Examples include parts of or substances produced by viruses or microorganisms (such as bacteria and protozoa), as well as substances in snake venom, certain proteins in foods, and components of serum and red blood cells from other individuals. Autoantigens, on the other hand, originate within the body. Normally, the body is able to distinguish self from nonself, but in persons with autoimmune disorders, normal bodily substances provoke an immune response, leading to the generation of autoantibodies. An antigen that induces an immune response—i.e., stimulates the lymphocytes to produce antibody or to attack the antigen directly—is called an immunogen.

Key People: Sir Peter B. Medawar Peter C. Doherty Rolf M. Zinkernagel (Show more) Related Topics: Why Are There Different Blood Types? epitope agglutinogen H-Y antigen Australia antigen (Show more) On the Web: Biology LibreTexts - Antigens (Feb. 18, 2026) (Show more) See all related content

On the surface of antigens are regions, called antigenic determinants, that fit and bind to receptor molecules of complementary structure on the surface of the lymphocytes. The binding of the lymphocytes’ receptors to the antigens’ surface molecules stimulates the lymphocytes to multiply and to initiate an immune response—including the production of antibody, the activation of cytotoxic cells, or both—against the antigen. The amount of antibody formed in response to stimulation depends on the kind and amount of antigen involved, the route of entry to the body, and individual characteristics of the host.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Adam Augustyn.