Apoptosis or programmed cell death is how multicellular organisms purposefully destroy and recycle their old, damaged or pre-cancerous cells. In human adults, roughly 70 billion cells are killed off every day through apoptosis. In this animation, a killer T cell — one of the foot soldiers of our bodies’ defence system — binds to the diseased cell using a special molecule or ligand. Akin to the Grim Reaper’s bony outstretched hand, the killer T cell’s death ligand triggers a cascade of chemical signals in the diseased cell which ultimately kills it. First, the diseased cell shrinks, and then breaks into small fragments, which are ‘eaten’ by other body cells. As well as being used to destroy damaged, malfunctioning cells, apoptosis also sculpts organs and tissue during development. Our fingers and toes are formed like gloves from mittens as cells apoptose between digits.
Written by Andrew Purcell
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences (the new name for the MRC Clinical Sciences Centre) the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.