Which statement best describes the innate immune system in terms of memory?

• A. It uses memory to improve responses upon re-exposure.
• B. It relies on clonal expansion of B and T cells.
• C. It produces high-affinity antibodies.
• D. It is non-specific and lacks memory.

Answer: (D)

Innate immunity provides an immediate, broad defense that recognizes general features of pathogens using pattern-recognition receptors. This response is non-specific and does not become more efficient after a previous encounter in the way adaptive immunity does. Memory is a hallmark of adaptive immunity, which relies on antigen-specific B and T cells and the production of high-affinity antibodies to mount a faster, stronger response upon re-exposure. The statement that best fits the innate system is that it is non-specific and lacks memory. The other ideas describe adaptive features—clonal expansion of B and T cells and production of high-affinity antibodies—which are not characteristics of the innate response. (Note: some discussions mention trained immunity, but classic definitions still treat innate memory as lacking.)