Which cells respond more quickly to a second antigen exposure than to the initial exposure?

• A. Thymocytes
• B. Monocytes
• C. Memory B cells
• D. Neutrophils

Answer: (C)

Memory B cells are the ones that respond more quickly to a second exposure because they carry antigen-specific information from the first encounter. After the initial exposure, some B cells become long-lived memory cells. When the same antigen appears again, these memory B cells rapidly recognize it and differentiate into antibody-secreting plasma cells, producing antibodies much faster and in greater amounts. This brisk, enhanced response is the hallmark of the secondary immune response, often with higher-affinity IgG antibodies due to prior exposure and affinity maturation.

The other options don’t fit this recall mechanism: thymocytes are immature T cells in the thymus, not memory B cells; monocytes are innate immune cells that act as phagocytes/presenters but don’t provide a rapid, antigen-specific secondary antibody response; neutrophils are frontline innate cells without memory for specific antigens.