Which molecule acts against a specific antigen?

• A. Antigen
• B. Antibody
• C. Basophil
• D. Cartilage

Answer: (B)

Antibody is the molecule that acts against a specific antigen. Antibodies are produced by B cells and have binding sites that fit a particular epitope on the antigen. This binding can neutralize the antigen directly and also marks it for destruction by other immune components, such as phagocytes or the complement system. The specificity comes from the antibody’s variable regions, which are tailored to recognize a specific antigen’s structure. An antigen is the target that triggers the immune response, not the agent that fights it. Basophils are immune cells involved in releasing histamine, and cartilage is connective tissue; neither acts against a specific antigen in the same targeted way as antibodies.