A hitchhiking, deadly fungus hacks the body’s immune system to spread to the brain. Breathing in airbone fungi, humans contract a lung disease called Cryptococcosis. When the infection starts, the first human cell to respond is a white blood cell called a macrophage, whose job it is to identify the fungus, destroy it, and alert the rest of the immune system. But in the case of Cryptococcosis, the invading fungus has evolved itself forward so that it can survive inside that white blood cell and hitchhike on its transportation system to move around the body. White blood cells can fight back, throwing the hitchhikers off the bus through a method called vomocytosis. In new research, scientists at the University of Birmingham, in collaboration with the Universities of Sheffield, Dundee, and Manchester in the UK, as well as the University of Leuven in Belgium and Harvard Medical School in the US , set out to identify how white blood cells in Zebrafish recognize and expel the potentially deadly hitchhikers. The scientists first identified signals that white blood cells use to control their behavior and then, one by one, disabled those signals. What they discovered was that one particular molecule, called ERK5, could be manipulated to encourage white blood cells either to throw out pathogens better or to keep them inside and try to kill them for longer. By blocking ERK5 in zebrafish, researchers were able to increase vomocytosis rates in their white blood cells and prevent the deadly fungal infection from spreading to the brain.The researchers hope the discovery will lead to the development of therapies that target this process, such as drugs that could limit an infection and prevent it from spreading from the initial site of attack.