Which of the following statements does NOT describe characteristics of the acquired immune system?

• A. It develops a response only after exposure to a substance recognized as nonself.
• B. It is the first line of defense against invading agents.
• C. Vaccination activates this system.
• D. It includes both antibody-mediated response and cell-mediated response.

Answer: (B)

The acquired immune system is highly specific and relies on exposure to an antigen to activate it. It develops memory so a second exposure triggers a faster, stronger response. Vaccination deliberately exposes the immune system to antigens to elicit this memory, engaging both B cells (antibody-mediated) and T cells (cell-mediated). It’s this adaptive, memory-oriented response that characterizes the acquired system as opposed to immediate, non-specific defenses. The first-line defense, on the other hand, is provided by the innate system with barriers and generic responses; that role is not a feature of the acquired immune system.