Fig. 4.

Macrophage-associated interplay between metabolism and the immune system in Drosophila. During homeostasis, macrophages are maintained in a basal number and at a basal metabolic level, playing essential roles to regulate lipid storage and organism growth through Pvf/Pvr signaling and JAK/STAT signaling. However, under stress conditions due to infection or nutrition deficiency, the immune system and other tissues compete for energy metabolism. Upon infection, the energy is reassigned to the immune system by inhibiting systemic metabolisms, which supports the rapid amplification of the macrophage population to defend against the pathogens. Likewise, when the nutrition is limited, the energy is reallocated toward the metabolic processes to ensure the survivability of the organism, and the number of macrophages is suppressed to save nutrients