In living organisms, no tissue acts in isolation. We address how multiple tissues work together in innate immunity and in the development and adaptation of the blood cell system, using the powerful model organism Drosophila melanogaster. In a recent project, we discovered a central role for a new blood cell reservoir at the respiratory epithelia of adult Drosophila. The reservoir serves as major receptacle of blood cells and foreign particles, and executes a local humoral immune response that is initiated by immune cell signaling. Other research in the lab focuses on blood cell transdifferentiation, where we dissect the central role of sensory neurons, their activity and signals, in the regulation of the blood cell pool related to vertebrate tissue macrophages.