Which of the following is an example of a hapten?

• A. Vaccines
• B. Poison ivy
• C. Glycoproteins
• D. Serum proteins

Answer: (B)

A hapten is a small molecule that, when combined with a larger carrier such as a protein, can elicit an immune response. Haptens on their own are not immunogenic; they need to bind to a larger molecule to become recognizable to the immune system. Poison ivy contains a specific compound called urushiol, which is a hapten. When it comes into contact with the skin, urushiol binds to proteins, creating a complex that the immune system recognizes as foreign, leading to an allergic reaction.

In contrast, vaccines generally contain antigens that are immunogenic and can provoke a direct immune response without needing to bind to a larger molecule. Glycoproteins are larger molecules that often play key roles in cell communication and can be immunogenic on their own. Serum proteins are typically larger proteins found in blood, which also can invoke immune responses but are not considered haptens. Therefore, poison ivy is a classic example of a hapten due to its ability to provoke an allergic reaction only when it interacts with skin proteins.