Which statement about active immunity is true?

• A. Temporary results from transfer of antibodies from outside of the body (passive immunity)
• B. Immunologic defenses developed by person's own body last many years, may last a lifetime
• C. Administration of antigens so patient actively mounts a protective immune response
• D. Immunity obtained from mother to infant through breastfeeding

Answer: (B)

Active immunity is when the body’s own immune system is stimulated to produce its own antibodies and memory cells in response to an antigen. This self-generated response tends to be long-lasting because memory B and T cells remain, providing protection for many years or even a lifetime.

That quality—long-lasting, self-produced protection—is what makes the statement about defenses developed by the person lasting many years the best description of active immunity. The other statements describe passive immunity (receiving antibodies from outside the body or from mother to infant), which is typically temporary, or describe a method to induce active immunity (such as vaccination) but don’t state the lasting, self-generated protection as clearly.