Programmed cell death.

Programmed cell death (PCD) is currently one of the most intensively studied areas in cell biology. Substantial evidence now exists demonstrating the integral role of PCD in many fundamental immunologic processes; therefore, understanding the mechanisms of PCD may provide advances with broad implications in immunobiology. This Overview provides a definition of PCD, a description of known PCD biochemical pathways, and finally a discussion of the implications of PCD in transplantation.