Do Memory B Cells Form Secondary Germinal Centers? Yes and No.

Memory is the defining feature of the adaptive immune system. Humoral immune memory is largely though not exclusively generated in the germinal center (GC), which spawns long-lived plasma cells that support ongoing serum antibody titers as well as "memory B cells" (MBCs) that persist in the immune host at expanded frequencies. Upon reencounter with antigen, these MBCs are reactivated and potentially can contribute to protection by further expansion, rapid differentiation to antibody-forming cells, and/or reseeding of a new round of GCs along with somatic V region mutation and selection. Here I will discuss what controls these various potential fates of MBCs and the functional significance of different types of MBC reactivation.