Which statement best describes memory B cells in vaccine-induced protection?

• A. Activation of cytotoxic T cells is the primary protective mechanism.
• B. Production of long-lived memory B cells and sustained antibody levels.
• C. Immediate innate phagocytosis is the main defense.
• D. Direct destruction of pathogens by neutrophils is required.

Answer: (B)

Memory B cells are formed when B cells encounter an antigen and receive help in germinal centers, undergoing affinity maturation and class switching. These memory cells persist for long periods and can rapidly differentiate into antibody-producing cells if the pathogen is encountered again, leading to a quick, strong antibody response. Vaccines aim to establish this memory and maintain antibody levels, in large part through long-lived plasma cells that continue to secrete antibodies over time. This combination provides durable protection, whereas relying primarily on cytotoxic T cells emphasizes a cellular response that's not the main driver of lasting humoral protection in many vaccines. Innate defenses like immediate phagocytosis or neutrophil activity act quickly but do not create antigen-specific, lasting memory.