Which term refers to any molecule that elicits an immune response?

• A. Antigen
• B. Pathogen
• C. Antibody
• D. Cytokine

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by understanding the key terms provided in the question. Each term represents a distinct concept in immunology. For example, 'antigen' refers to a molecule that triggers an immune response, 'pathogen' is an organism that causes disease, 'antibody' is a protein produced by the immune system to neutralize antigens, and 'cytokine' is a signaling molecule involved in immune communication.
2. Step 2: Focus on the phrase 'elicits an immune response' in the question. This means the molecule must directly stimulate the immune system to react, which is a defining characteristic of an antigen.
3. Step 3: Compare the definitions of the terms. While pathogens can cause disease and indirectly lead to an immune response, they are not the molecules that directly stimulate the immune system. Antibodies are produced as a result of the immune response, not the cause of it. Cytokines are signaling molecules that regulate immune responses but do not directly elicit them.
4. Step 4: Based on the comparison, identify the term that matches the definition of a molecule that directly triggers the immune system. This term is 'antigen.'
5. Step 5: Conclude that the correct answer is 'antigen,' as it is the molecule responsible for eliciting an immune response, distinguishing it from the other options provided.