Question

What are Haptens?

• A. Antigens which induce low immune response
• B. Antigens which are not immunogenic on their own
• C. Antigens which induce high immune response
• D. Antigens which are nonspecific stimulators of immune response

Hint:

• Antigen Any substance that can be bound by an antibody or T-cell receptor.
• Immunogen An antigen that can elicit an immune response (antibody production, T-cell activation).
• Hapten A small molecule that is antigenic (can bind to antibodies) but not immunogenic on its own. It becomes immunogenic when coupled to a larger carrier molecule.
• Example: Penicillin can act as a hapten, leading to allergic reactions in some individuals when it binds to host proteins.

Answer 1

The Correct Option is B

A hapten is a small molecule that can elicit an immune response (e.g., antibody production) only when attached to a larger carrier molecule, such as a protein. Key characteristics of haptens:

• Antigenic but not Immunogenic on their own: Haptens can be recognized by antibodies (they are antigenic or can act as epitopes), but they are too small to induce an immune response (i.e., stimulate antibody production or T-cell activation) by themselves (they are not immunogenic alone).
• Require a Carrier: To become immunogenic, a hapten must be covalently bound to a larger carrier molecule (usually a protein like albumin or keyhole limpet hemocyanin - KLH). The hapten-carrier conjugate is then immunogenic.
• Antibodies produced against the hapten-carrier conjugate can include antibodies specific for the hapten, antibodies specific for the carrier, and antibodies specific for the conjugate.

Let's analyze the options: (a) "Antigens which induce low immune response": Some antigens are weakly immunogenic, but this doesn't define a hapten. Haptens are *not* immunogenic *at all* on their own. (b) "Antigens which are not immunogenic on their own": This correctly describes haptens. They can bind to antibodies (are antigenic) but need a carrier to stimulate an immune response. (c) "Antigens which induce high immune response": This describes strong immunogens, not haptens. (d) "Antigens which are nonspecific stimulators of immune response": This might describe adjuvants or polyclonal activators (like mitogens), not haptens. Therefore, haptens are antigens that are not immunogenic by themselves but become immunogenic when conjugated to a carrier. \[ \boxed{\text{Antigens which are not immunogenic on their own}} \]