Memory in adaptive immunity refers to what?

• A. Short-term recall by innate cells
• B. Long-lived B and T cells that respond more rapidly upon re-exposure to the same antigen
• C. Production of antibodies by plasma cells only during primary response
• D. Immediate but weak response to any antigen

Answer: (B)

Memory in adaptive immunity means long-lived B and T cells persist after an initial encounter and enable a faster, stronger response when the same antigen is encountered again. After the first exposure, some B cells become memory B cells and some T cells become memory T cells, while others become antibody-secreting plasma cells. Upon re-exposure, these memory cells rapidly react, proliferate, and differentiate, producing antibodies more quickly and mounting a more effective cellular response. This is why secondary responses are quicker and more robust due to prior exposure and affinity maturation.

The other statements don’t fit because memory is a feature of adaptive immunity, not innate innate recall. Plasma cells are produced during both primary and secondary responses, not exclusively the primary one. And memory responses are characterized by speed and strength, not an immediate but weak reaction to any antigen.