Figure 1.

Engulfment signaling mediates sick cell killing or tolerance. (A) C. elegans engulfment signaling pathways leading to the activation and subsequent inactivation of CED-10 (GTP- and GDP-bound, respectively). Solid and dashed arrows, characterized and unknown signaling events, respectively. (B) Sick cell killing vs. tolerance model. Cells containing the ability to engulf constantly survey their neighbors. Depending on the ‘fitness’ of a particular neighbor, the engulfing cell either tolerates, or—if necessary—actively kills and engulfs the unhealthy neighbor, thereby ensuring the fitness of the entire cell community or tissue.