Foreign substances that elicit an immune response are termed:

• A. Cytokines
• B. Antigens
• C. Phagocytes
• D. Antibodies

Answer: (B)

Verified step by step guidance

1. Step 1: Begin by understanding the key terms provided in the problem. The question asks about 'foreign substances that elicit an immune response.' This means we are looking for a term that describes molecules or entities recognized by the immune system as non-self, triggering a defense mechanism.
2. Step 2: Review the definitions of the options provided: - Cytokines: These are signaling proteins released by cells, especially immune cells, to regulate immunity, inflammation, and hematopoiesis. They do not directly refer to foreign substances. - Antigens: These are molecules or substances (often proteins or polysaccharides) on the surface of pathogens or foreign particles that are recognized by the immune system and elicit an immune response. - Phagocytes: These are immune cells (e.g., macrophages) that engulf and digest foreign particles, pathogens, or debris. They are not foreign substances themselves. - Antibodies: These are proteins produced by B cells in response to antigens. They bind specifically to antigens to neutralize or mark them for destruction.
3. Step 3: Focus on the term 'foreign substances.' Among the options, 'antigens' is the term that directly refers to foreign substances that trigger an immune response. The other terms describe components or actions of the immune system but do not fit the definition of foreign substances.
4. Step 4: Recall examples of antigens to solidify understanding. Antigens can include parts of bacteria, viruses, fungi, or toxins. For instance, the protein coat of a virus or the lipopolysaccharide layer of certain bacteria can act as antigens.
5. Step 5: Conclude that the correct term for foreign substances that elicit an immune response is 'antigens,' based on the definitions and examples provided.