Conserved microRNA miR-8 in fat body regulates innate immune homeostasis in Drosophila

► Elevation of antimicrobial peptides (AMPs) by miR-8 loss in non-immunized state. ► Ectopic melanization occurs in miR-8 null flies without immune challenge. ► Increase of Drosomycin in miR-8 null larva is fat body organ specific. ► Re-introduction of miR-8 into fat body rescues the systemic AMP alteration. ► miR-8 in fat body regulates systemic AMP homeostasis independently of PI3K.