When pathogens invade the body, the immune system must react immediately to prevent or contain an infection. But how do our defence cells stay ready when no attacker is in sight? Scientists from Vienna have found a surprising explanation: They are constantly stimulated by healthy tissue. This keeps them active and ready to respond to pathogens. Based on this insight, future medications could be devised to selectively enhance our immune system’s attention. The study has been published in the journal Nature Immunology.