Cognate interactions between Ag-specific B cells, CD4+ T helper cells, and DCs in response to foreign Ag lead to the formation of germinal centers (GCs). GCs are specialized structures in B cell follicles of secondary lymphoid tissues
where somatic hypermutation of Ig variable (V) region genes and selection of high-affinity B cells occur, followed by differentiation of longlived memory or plasma cells (PC). This process ensures the development of long-lived humoral
immunity after infection or vaccination with T cell–dependent (TD) Ag and is a unique feature of the mammalian immune system