Jeannette Tenthorey is investigating how mammals’ immune systems stop bacterial invaders from growing. One family of immune proteins unravels molecular strings that some bacteria use to travel through infected cells. Tenthorey has identified rapidly evolving changes in these immune proteins – a sign that they are mutating to counteract bacterial attempts to evade or destroy them. She plans to determine the specific mutations that help these proteins resist attack. The work could offer new tools for halting bacterial growth.