Mature B cells: apoptosis checkpoints.

In the present review, the apoptosis mechanisms that ensure efficiency of the B cell responses and homeostasis of mature B cells are examined. The general scheme that emerges from the literature is that these two phenomena are under the control of distinct apoptotic pathways. The extrinsic death receptor pathway intervenes in the quality control of the B cell response to thymus-dependent antigens. It prevents the bystander activation of irrelevant B cell clones and is instrumental in the affinity maturation of the antibody response. The intrinsic death pathway is responsible for homeostasis of the naive, effector, and memory B cell compartments. Recent results suggest the stress signal that triggers this pathway may be initiated by different cellular organelles depending on the B cell developmental stage.