Which of the following best describes an antigen?

• A. A protein produced by B cells that binds specifically to pathogens
• B. A chemical substance used to kill bacteria on surfaces
• C. A type of white blood cell that engulfs pathogens
• D. A molecule that is recognized by the immune system and can trigger an immune response

Answer: (D)

Verified step by step guidance

1. Understand the definition of an antigen: An antigen is any molecule or molecular structure that can be recognized by the immune system and can trigger an immune response.
2. Review the options given and identify key terms: Look for descriptions involving recognition by the immune system or triggering immune responses.
3. Eliminate options that describe other immune components or unrelated substances, such as proteins produced by B cells (which are antibodies), chemicals that kill bacteria (disinfectants), or white blood cells that engulf pathogens (phagocytes).
4. Focus on the option that describes a molecule recognized by the immune system and capable of triggering an immune response, as this matches the definition of an antigen.
5. Conclude that the best description of an antigen is a molecule recognized by the immune system that can trigger an immune response.