A cell capable of exploding like a tiny biological grenade has just been identified in flatworms.
Named "ruptoblast," it sacrifices itself to release toxic substances. These quickly destroy neighboring cells and certain bacteria. This immune strategy, described by researchers at Stanford University, does not resemble any known cellular mechanism to date.
The discovery was made in planarians, small aquatic worms known for their regenerative abilities. After an injury, these animals can rebuild organs, or even reform an entire body. Scientists were studying their reaction to foreign tissues when they observed cells suddenly disappearing, surrounded by a zone of destruction.
To trigger this reaction, the team had fused pieces from two different planarians. The new organism then progressively rejected the foreign tissues, similar to transplant rejection. This response was accompanied by strong inflammation and an increase in activin, a hormone involved in several biological functions in these animals.
Under the effect of a high concentration of activin, certain ruptoblasts begin to swell before bursting. This phenomenon, named "ruptosis," occurs in a matter of seconds or minutes. The cell then releases diffusible toxic agents and almost completely disappears. A single explosion can kill several dozen cells located in its immediate vicinity.
Other cells can also rupture upon their death, but the process is generally slower. Pores progressively appear in their membrane, allowing their contents to leak out over several hours. Ruptosis is much more sudden. Researchers thus present it as the fastest explosive form of cell death observed to date.
Ruptoblasts also destroyed Escherichia coli bacteria, human kidney cells, and mouse blood cells in the laboratory. Their action remains, however, very localized: the released substances quickly lose their toxicity and do not trigger a chain reaction.
The researchers now plan to study the substances released during ruptosis. Such a localized mechanism could inspire methods capable of targeting bacteria or tumor cells.