Which of the following best describes an antigen?

• A. A protein produced by B cells to neutralize pathogens
• B. A type of white blood cell that engulfs pathogens
• C. A molecule that is recognized by the immune system and can trigger an immune response
• D. A chemical signal that attracts immune cells to the site of infection

Answer: (C)

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: For example, 'a protein produced by B cells' refers to antibodies, not antigens; 'a type of white blood cell that engulfs pathogens' refers to phagocytes like macrophages; 'a chemical signal that attracts immune cells' refers to cytokines or chemokines.
3. Recall that antigens are typically foreign molecules such as proteins or polysaccharides found on the surface of pathogens that the immune system detects.
4. Match the correct description to the definition of an antigen: The option stating 'a molecule that is recognized by the immune system and can trigger an immune response' aligns with the scientific definition of an antigen.
5. Conclude that the best description of an antigen is the molecule recognized by the immune system that triggers an immune response, distinguishing it from antibodies, immune cells, or signaling molecules.