Immune cell extrudes a webbing that can encourage the growth of gallstones, a common and painful malady.

The hard lumps called gallstones can be as large as golf balls and cause intense pain, but new insights suggest a way to stop their growth.

Gallstones are pebble-like deposits of digestive fluid that form in the gallbladder. To understand how they form, Martin Herrmann at University Hospital Erlangen in Germany and his colleagues studied human gallstones that had been removed during surgery.

The team found that the stones’ surfaces were riddled with crystals of calcium and cholesterol — the basic ingredients of gallstones — mixed with DNA. Experiments on the gallstones showed that neutrophils, a type of white blood cell activated by infection, can produce net-like structures that are made mostly of genetic material and trap calcium and cholesterol.

The researchers gave one group of mice an existing drug that reduces neutrophil activity and another group a compound that blocks the cells’ formation of the net-like structures. In both groups, gallstone growth was slower than it was in untreated mice.

The authors’ findings suggest that a drug against gallstones could be just around the corner.