Eating oneself and uninvited guests: autophagy-related pathways in cellular defense.

The eukaryotic cell uses an evolutionarily conserved lysosomal pathway of self-digestion (autophagy) for survival when extracellular nutrients are limited. In this issue of Cell, new evidence indicates that autophagy is used to for survival when intracellular nutrients are limited by growth factor deprivation (Lum et al., 2005). Other recent studies indicate that the autophagy machinery is also used to degrade foreign microbial invaders (xenophagy).