Immune defense in Drosophila has humoral and cellular components that act effectively to control infectious organisms through the production of antimicrobial proteins and the phagocytosis and encapsulation of invading organisms (reviewed in 9). The main tissue of humoral immune defense is the fat body, which corresponds to the mammalian liver. Cellular immune defense is mediated by the hematopoietic system, which consists of hemocytes and lymph glands.