What is apoptosis and why is it beneficial for cells to clean themselves up?

Every day, billions of cells in your body die in an orderly, quiet way. This is called apoptosis: a built-in self-destruction programme that the body uses to remove damaged, aged or redundant cells. The cell shrinks, breaks down neatly, and is cleared away by surrounding cells. No inflammation is involved.

That is precisely the difference from unwanted cell death, such as during a heart attack. In that case a cell swells and bursts open, which does trigger a substantial inflammatory response and causes additional tissue damage. Apoptosis is the tidy alternative: everything is handled without making a mess.

Apoptosis is essential at two moments. During the formation of the body, redundant cells are cut away through apoptosis, quite literally the way the skin between your fingers disappears. After birth, the mechanism keeps tissue healthy by replacing aged or damaged cells. Apoptosis also helps during infections: by allowing infected cells to die off before a virus or bacterium can spread further, the body limits the damage.

The balance is critical, however. Too little apoptosis and cells that should really be removed keep dividing, which can contribute to cancer. Too much apoptosis and the body clears away its own still-healthy cells. The latter plays a role in brain diseases such as Alzheimer's and after a stroke: adult nerve cells can barely renew themselves, so every neuron that is needlessly lost is a permanent loss.

Apoptosis is also not the only form of programmed cell death. Variants exist that do trigger inflammation, and these play a role in serious infections such as sepsis. The interplay between these different pathways makes targeted intervention difficult. Existing and future research is focused on restoring the balance, but concrete treatments are not yet widely available.