Rat cells’ immune response has been switched on and off with a magnetic field, a technique that could control treatment of allergies and other illnesses more precisely.

Children’s Hospital in Boston researchers created iron nanobeads that bind to receptor molecules on the surface of rats’ immune cells. When exposed to a magnetic field, the beads cluster together, pulling the receptors with them. Changes to the receptors due to aggregation set off a series of chemical reactions that trigger the cell’s immune response.

Many drugs work by triggering aggregation, but nanobeads and the magnetic field allow the process to be stepped up or switched off.