Definition

1. Noun:
   • A substance that triggers an immune response: An antigen is any substance, such as a toxin, enzyme, or part of a pathogen, that the body recognizes as foreign. This recognition stimulates the immune system to produce a specific response, most notably the production of antibodies.

Usage Examples

• Noun:
  • The vaccine contains a weakened form of the viral antigen to train the immune system.
  • Doctors tested her blood for the presence of the antigen to confirm the infection.
  • Each specific antigen prompts the body to create matching antibodies.

Advanced Usage

• "Self-antigen": An antigen that originates within the body. Normally, the immune system does not attack self-antigens.

  • Autoimmune diseases occur when the body mistakenly attacks its own self-antigens.

• "Antigen-presenting cell (APC)": A specialized cell, such as a macrophage or dendritic cell, that displays an antigen on its surface to activate other immune cells.

  • Dendritic cells are crucial antigen-presenting cells that initiate the adaptive immune response.

Variants and Related Words

• Antigenic (adj): Relating to or having the properties of an antigen.

  • The virus undergoes frequent antigenic changes, making vaccine development challenging.

• Antigenicity (n): The capacity of a substance to act as an antigen; to induce an immune response.

  • The antigenicity of the protein determines how strong an immune response it will provoke.

Synonyms

• Immunogen: A substance capable of provoking an immune response. (Note: All immunogens are antigens, but not all antigens are strongly immunogenic.)
• Allergen: A type of antigen that produces an abnormally vigorous immune response (an allergy).

Related Phrases and Concepts

• Antigen-antibody reaction: The specific binding between an antigen and its corresponding antibody.

  • The antigen-antibody reaction is fundamental to many diagnostic tests.

• Antigenic determinant (epitope): The specific part of an antigen molecule that is recognized and bound by an antibody.

  • An antibody binds only to a specific epitope on the antigen.

Noun

1. any substance (as a toxin or enzyme) that stimulates an immune response in the body (especially the production of antibodies)