Researchers from Ben-Gurion University and Stanford University have identified a new kind of immune cell in flatworms that defends the body by blowing itself up. The cells, called repotoblasts, react to a sharp rise in the hormone activin, which signals distress, and then trigger a chain reaction that ends in an explosive release of toxic compounds. Those compounds can kill nearby cells within minutes.
The study, published in Cell and led by Prof. Benjamin Rosenthal of Ben-Gurion University and Prof. Bo Wang of Stanford, began with microscopes showing cells disappearing rapidly and leaving behind fields of dead cells. The team found that the process is tightly controlled, since the biochemical switch is activated only by activin, and the harmful substances naturally break down within about 15 minutes, reducing the chance that surrounding cells will be accidentally destroyed.
In lab tests, a single immune cell killed up to 70 neighboring cells, including bacteria, flatworm cells, mammalian cells, and even human cancer cells. Wang said, “The speed and completeness of the destruction really surprised us,” adding that the blast releases a wave of powerful, broad-spectrum killing agents. Rosenthal said the findings reveal “a completely new strategy” that directly links hormonal signals to explosive immune defense and could inspire engineered cell therapies against harmful bacteria or abnormal cells.
The researchers also found repotoblasts in planarians, flatworms known for their regeneration, which lack antibodies but still mount strong defenses against foreign organisms. When the worms were exposed to bacteria, nearby immune cells released activin, triggering the repotoblasts and rapidly rupturing microbial membranes. Mixing tissue from two different flatworms caused severe activin buildup, mass explosions, and tissue lesions, but removing repotoblasts genetically stopped the destructive rejection entirely. The study was supported by the European Research Council, the U.S. National Institutes of Health, and the Human Frontier Science Program.
