# antigen

/ˈæntədʒən/ (US) · /ˈæntɪdʒˌɛn/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/antigen
Updated: 2026-05-07

## Definition

a substance that makes your immune system start fighting, often by creating antibodies. It is usually something from outside your body, like a virus or bacteria.

For teachers: any substance that induces an immune response in the body, specifically the production of antibodies. Typically a protein or polysaccharide on the surface of a pathogen.

## Examples

- The vaccine introduces a harmless antigen to your body.
- Doctors use a rapid test to detect the presence of a specific viral antigen in the patient's blood sample.
- The immune system distinguishes between self and non-self by recognizing unique molecular patterns on the surface of the invading antigen, triggering a targeted defensive response.

## Usage notes

- Commonly used in medical and biological contexts; often paired with verbs like 'detect', 'recognize', or 'bind'.

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