Follicular dendritic cells and apoptosis: life and death in the germinal centre.

The germinal centre forms a specialized microenvironment thought to play a key role in the induction of antibody synthesis, affinity maturation of B cells and memory B cell formation. Clonal-expanded follicular B lymphocytes with mutated antigen receptors (centrocytes) have to be selected on the basis of their capacity to compete for binding to antigen held in limited amounts on the follicular dendritic cells. In this way, only high-affinity B cells are selected. Binding to a follicular dendritic cell is an unconditional prerequisite for centrocytes to survive. Cells that do not succeed in binding to a follicular dendritic cell die rapidly by apoptosis. Apoptosis is a common form of cell death characterized by the activation of an endonuclease culminating in nuclear destruction. The pathway by which apoptosis is triggered varies from cell type to cell type. However, for germinal centre B cells this process is still poorly understood.