Later exposure to the same foreign substance elicits which type of immune response due to memory?

• A. Primary response
• B. Autoimmune response
• C. Tolerance
• D. Secondary response

Answer: (D)

Memory from prior exposure allows the immune system to respond faster and more strongly the next time the same antigen appears. After the first encounter, the adaptive immune system creates memory B and T cells that persist. When re-exposed, these memory B cells quickly become plasma cells and produce large amounts of high-affinity antibodies, while memory T cells streamline the helper and cytotoxic responses. This rapid, robust reaction is the secondary immune response (anamnestic response). It is faster and yields a higher antibody titer than the initial encounter, which is the primary response and tends to be slower with antibodies starting as IgM before switching to IgG.