What type of cells can initiate a rapid immune response upon re-exposure to an antigen?

Memory B cells are specialized cells that play a crucial role in the immune system's ability to respond quickly and effectively upon re-exposure to a specific antigen. When the body encounters an antigen for the first time, B cells are activated to produce antibodies and some of these cells differentiate into memory B cells. These memory B cells persist long after the initial infection has been cleared, allowing for a faster and more robust immune response if the same pathogen is encountered again.

Upon re-exposure, memory B cells can rapidly differentiate into plasma cells that produce large quantities of antibodies specific to the antigen, often within a matter of days. This quick response is significantly faster than the primary immune response, which takes longer to develop due to the time needed for naive B cells to activate, proliferate, and differentiate.

Other cell types mentioned in the question have different roles in the immune response. Macrophages primarily function as antigen-presenting cells that can initiate a response but do not store memory. Natural killer cells are involved in the innate immune response and target infected cells but do not provide long-term memory. T-helper cells assist other cells in the immune response but do not directly produce antibodies or respond independently to antigens. Thus, memory B cells are uniquely equipped to initiate a