The immune response in Drosophila: pattern of cecropin expression and biological activity.

Abstract

Cecropins are antibacterial peptides, induced in Drosophila as part of the humoral immune response to a bacterial invasion. We have used the cloned Drosophila cecropin genes CecA1, A2 and B as probes to study the developmental and tissue specific regulation of this response. The genes are strongly expressed in fat body and hemocytes after injection of bacteria, the CecA genes being much more active than CecB in the fat body. All parts of the fat body and 5‐10% of the hemocytes are involved in this response. CecA1 and A2 are most active in larvae and adults; CecB is preferentially active in early pupae. A small peak of constitutive cecropin expression in early pupae appears to be caused by bacteria in the food. Cecropin A, the common product of the CecA1 and A2 genes, was identified in the hemolymph of immunized flies at a concentration of 25‐50 microM, enough to kill all tested bacteria except Serratia, a Drosophila pathogen. A useful in vitro system to study the immune response has been found in Schneider's line 2 cells which respond to lipopolysaccharide and laminarin by cecropin expression.

The humoral antibacterial response of Drosophila

“…Studies performed on the expression profiles of the genes encoding cecropins [19,20,23], diptericin [21], defensin [25] and drosocin [24] in bacteria-challenged Drosophila yielded results similar to those obtained in other species of the recent insect orders (namely in Hvalophora cecropia (reviewed in [15]), Munduca sexta [26], Sarcophuga peregrina [ 11,27-291, Phormia terranovae [30]). The genes are rapidly transcribed following challenge (1 to 2 h), the transcription rate increases over a period varying between 6 and 24 h, depending on the gene, and thereafter either stops or levels off.…”

“…In association with Hultmark's group, we isolated in 1990 [19,20,23] and diptericin [21] were deduced from DNA cloning studies; cecropin A was directly isolated from immune adults of Drosophila in our laboratory and the deduced sequence [19] was confirmed by Edman degradation and molecular mass determination (m/z = 4155.2). Bold residues differ among the three expressed cecropins [19,20,23]. We suspect diptericin to be post translationally modified by 0-glycosylation, as demonstrated in the case of diptericin from the fleshfly Phormia terranovae (unpublished).…”

Structural and functional characterization of pseudopodocyte, a shaggy immune cell produced by two Drosophila species of the obscura group

“…Their cytoplasm encloses a well-developed Golgi apparatus, a rough endoplasmic reticulum (RER) developed in large cisternae, numerous free ribosomes, lipidic vesicles, and phagolysosome-like inclusions (Ribeiro and Brehélin, 2006). Plasmatocytes are involved in phagocytosis, wound healing, production of antimicrobial peptides and, probably, in foreign body recognition, too (Brehélin, 1982;Franc et al, 1999;Ribeiro and Brehélin, 2006;Samakovlis et al, 1990;Dimarcq, 1997;Tzou et al, 2002;Meister, 2004;Charoux and Royet, 2009). They also contribute to encapsulation: they were shown attaching to the chorion of a parasitoid egg within a few hours after parasitization, thus being the first cells to come in contact with the foreign body at the very beginning of capsule formation (Russo et al, 1996;Williams et al, 2005).…”

CecC, a cecropin gene expressed during metamorphosis in Drosophila pupae

“…In vaccinated larvae and adults, most of the cecropin mRNA comes from two of the genes, CecAl and CecA2, whereas the third gene, CecB, is much less active. At these stages, the fat body was shown to be the major site of synthesis although some transcription could also be demonstrated in hemocytes [4]. In the early pupa, a different pattern of cecropin gene expression was evident.…”

“…Corre.spndence fo D. Hultmark induced pupae, some expression was observed in the fat body [4], but the situation appeared to be more complex and transcripts were also detected elsewhere.…”