Allergens differ from antigens because:

• A. allergens are produced by the body, while antigens are always foreign substances
• B. allergens are recognized only by B cells, while antigens are recognized by T cells
• C. allergens specifically trigger hypersensitivity reactions in the immune system
• D. allergens are always proteins, whereas antigens can be any type of molecule

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the definitions of antigens and allergens. Antigens are any molecules that can be recognized by the immune system and trigger an immune response. Allergens are a specific type of antigen that cause hypersensitivity or allergic reactions.
2. Step 2: Analyze the first option: 'allergens are produced by the body, while antigens are always foreign substances.' This is incorrect because allergens are typically foreign substances, not produced by the body.
3. Step 3: Analyze the second option: 'allergens are recognized only by B cells, while antigens are recognized by T cells.' This is incorrect because both B cells and T cells can recognize antigens, including allergens.
4. Step 4: Analyze the third option: 'allergens specifically trigger hypersensitivity reactions in the immune system.' This is correct because allergens are antigens that cause exaggerated immune responses known as hypersensitivity or allergic reactions.
5. Step 5: Analyze the fourth option: 'allergens are always proteins, whereas antigens can be any type of molecule.' This is not entirely accurate because while many allergens are proteins, some can be other types of molecules, and antigens can also be proteins, polysaccharides, lipids, or nucleic acids.