What is the significance of memory cells in immunity?

• A. They produce antibodies immediately
• B. They remember specific antigens and enable a faster immune response upon re-exposure
• C. They only function during the initial exposure
• D. They are responsible for histamine release

Answer: (B)

Memory cells carry the signature of past encounters with antigens and are central to long-term immunity. After the first exposure, some B and T cells that recognize the antigen persist as memory cells. When the same antigen appears again, these cells respond much more rapidly and robustly, proliferating and differentiating into antibody-producing cells (and cytotoxic cells if needed) so the body can neutralize the threat before it causes illness. This accelerated, higher-affinity secondary response is the basis for lasting protection and why vaccines can provide long-term immunity.

The other options don’t fit because memory cells aren’t the cells that produce antibodies immediately during the first encounter (that’s the job of plasma cells), they aren’t active only during the initial exposure, and they aren’t responsible for releasing histamine (which involves mast cells and basophils).