Think of it as communicating with Silly String. When some of our white blood cells detect viruses or other microbes that have invaded our bodies, they may alert other cells to the threat by spraying out some of their DNA. This unexpected warning system, described in a study out this week, could hasten the body’s response to pathogens.

“It might be a new way for immune cells to detect infections and get rid of them,” says innate immunologist Paul Kubes of the University of Calgary in Canada, who isn’t connected to the study.

Researchers already know that some of our cells deploy DNA to directly fight infections. Immune cells known as neutrophils can eject their DNA, forming a mesh of sticky strands called a neutrophil extracellular trap (NET) that captures and kills microbes. Other immune cells generate similar DNA snares. The material for these traps often comes from the nucleus, but it can also spring from mitochondria, cells’ energy-producing power plants.

In the new study, a team led by biochemist Björn Ingelsson and immunochemist Anders Rosén of Linköping University in Sweden investigated whether NETs might also spur the growth of cancerous white blood cells in one type of leukemia—something scientists had previously hypothesized. While testing that idea, the researchers noticed something peculiar about cancerous cells that had been removed from leukemia patients and were growing in lab dishes.

The abnormal white blood cells—known as B cells—sometimes released skeins of DNA similar to NETs. These DNA webs, as the researchers call them, weren’t just a quirk of leukemia cells. The scientists demonstrated that B cells from healthy people also squirt out DNA in response to the distinctive molecular patterns that occur in many bacteria and viruses. Four other types of white blood cells also produce the webs, the team reported online this week in the Proceedings of the National Academy of Sciences. Sequencing the discharged DNA showed that it came from mitochondria, not the nucleus.