Which term refers to molecules that activate adaptive immunity?

• A. Antigens
• B. Antibodies
• C. Immunogens
• D. Epitopes

Answer: (C)

Immunogens are the molecules that trigger the adaptive immune response by being recognized and processed in a way that activates B and T cells, leading to clonal expansion and memory. They must be presented with the right signals from antigen-presenting cells to provoke a full, specific immune response. This category includes many proteins, polysaccharides, and even some lipids that can elicit immunity; note that very small molecules (haptens) can become immunogenic only when linked to a larger carrier protein.

Antigens, in contrast, are anything that can be recognized by the immune system, but not every antigen will necessarily provoke a strong immune response on its own. Epitope refers to the specific part of an antigen that binds to an antibody or T cell receptor—the precise binding site, not the whole molecule. Antibodies are the immune system’s effector proteins produced in response to immunogens.