Which immune cell subset is responsible for the rapid secondary antibody response upon re-exposure to an antigen?

• A. Memory B cells
• B. Regulatory T cells
• C. Natural killer cells
• D. Macrophages

Answer: (A)

The key idea is immunological memory driving a faster, stronger humoral response. After the first exposure, B cells that specifically recognize the antigen become memory B cells and some differentiate into long-lived cells that await a second encounter. When the same antigen is encountered again, these memory B cells rapidly react, proliferate, and differentiate into antibody-secreting plasma cells, producing large amounts of high-affinity antibodies quickly. This rapid secondary antibody production relies on the preprogrammed, high-affinity B cells built during the primary response.

Other cell types don’t drive this rapid antibody surge. Regulatory T cells modulate and suppress immune responses; natural killer cells are innate cytotoxic cells; macrophages are phagocytes and antigen-presenting cells that help initiate responses but don’t mediate the quick, high-volume antibody production seen on re-exposure.