Differentiation and cell death: lessons from the immune system.

The immune system provides a unique vantage point from which to view the interrelationship between differentiation and cell death, as apoptosis is a prominent feature of B- and T-lymphocyte development. Two common themes emerge from recent experimental observations. First, survival signals are crucial during the differentiation process. The upregulation of Bcl-2 during positive selection suggests that this molecule serves as a survival signal to maintain lymphoid homeostasis. Second, if cell death is repressed, cellular differentiation can occur in the absence of inductive signals.