Memory B cell

A memory B cell is a long-lived lymphocyte that persists after an initial immune response and enables rapid, amplified secondary responses upon re-encounter with the same antigen. Unlike naive B cells, memory cells have undergone clonal selection and affinity maturation in the germinal center, giving them higher receptor affinity and lower activation thresholds. They circulate between blood, lymph, and tissues as a distributed archive of immunological experience.

The existence of memory B cells transforms the immune system from a purely reactive network into a learning system with temporal depth. Their persistence is measured in years to decades, yet the mechanisms that sustain their longevity remain incompletely understood. The population is not static: some memory cells differentiate into plasma cells upon reactivation, while others self-renew to maintain the memory pool. This bifurcation is itself a decision whose logic — why one cell becomes an effector while another remains memory — is one of the open questions in immunology.