Immune defence mechanisms exist across the tree of life in such a wide diversity that the immune mechanisms of bacteria (antiphage systems) were considered unrelated to immunity of eukaryotes. However, recent discoveries unveiled hundreds of novel antiphage systems. Among this diversity of novel bacterial immune mechanisms, it emerged that a subset of antiphage defense systems are conserved in eukaryotes and are major actors of diverse immune pathways, leading us to revisit this paradigm. I will discuss the evolutionnary dynamics of immunity across domains of life and how the conservation of immune modules in bacteria, plants and animals can lead to discoveries in prokaryotes and eukaryotes.