The Host Defense of Drosophila melanogaster

Abstract

To combat infection, the fruit fly Drosophila melanogaster relies on multiple innate defense reactions, many of which are shared with higher organisms. These reactions include the use of physical barriers together with local and systemic immune responses. First, epithelia, such as those beneath the cuticle, in the alimentary tract, and in tracheae, act both as a physical barrier and local defense against pathogens by producing antimicrobial peptides and reactive oxygen species. Second, specialized hemocytes participate in phagocytosis and encapsulation of foreign intruders in the hemolymph. Finally, the fat body, a functional equivalent of the mammalian liver, produces humoral response molecules including antimicrobial peptides.Here we review our current knowledge of the molecular mechanisms underlying Drosophila defense reactions together with strategies evolved by pathogens to evade them.

Bacterial strategies to overcome insect defences

“…In D. melanogaster, the synthesis of immune effectors by the fat body is under the control of the Toll and Imd signalling pathways 93 . Each of these pathways activates specific nuclear factor (NF)-κB transactivators, which in turn switch on specific programmes of transcription.…”

Senescence of the cellular immune response in Drosophila melanogaster

“…Pathogen detection is followed by cellular and humoural responses. The principal component of the humoural immune response is the systemic and local production of antimicrobial peptides (AMPs) [10].…”

Prostaglandin E2 modulates the expression of antimicrobial peptides in the fat body and midgut of Anopheles albimanus

“…Hemocytes also encapsulate those invaders, such as parasitoid eggs, too big to phagocytose (Stanley, 2006;Stanley and Miller, 2006). These cellular defense mechanisms are practically immediate upon microbial invasion, but complex humoral responses, including hemolymph clotting (Blandin and Levashina, 2004), melanization, and the production of antimicrobial peptides (Yu and Kanost, 2003;Lemaitre and Hoffmann, 2007) are deployed later.Eicosanoids including prostaglandins (PGs) are fatty acid metabolites that in mammals are produced by many cell types, including epithelial and immune cells, and play key roles in hemostasis and immune regulation, among many other functions (Harris et al, 2002). The biosynthesis of PGs in insects is initiated by a phospholipase A 2 (PLA 2 ) that cleaves membrane phospholipids (C20 polyunsaturated fatty acids including arachidonic acid [AA]), and the resulting products are converted to PGs' bioactive forms by cyclooxygenases (COX) (Stanley, 2000(Stanley, , 2006, but products of the lipoxygenase pathway (LOX) have been also documented (Galdelhak et al, 1995).…”