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Programmed cell death is first observed at stage 11 of embryogenesis in Drosophila. The systematic removal of apoptotic cells is mediated by cells that are derived from the procephalic mesoderm and differentiate into macrophages. We describe a macrophage receptor for apoptotic cells. This receptor, croquemort (catcher of death), is a member of the CD36 superfamily. Croquemort-mediated phagocytosis represents the concept that phagocytosis evolved primarily as a cellular process for the removal of effete cells. Our findings support the idea that the primordial function of macrophages may have been in tissue modeling and that their adapted role is in host defense.

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We have isolated from the hemolymph of immunized larvae of the dipteran insect Phormia terranovae two peptides that are selectively active against Gram-positive bacteria. They are positively charged peptides of 40 residues containing three intramolecular disulfide bridges and differ from one another by only a single amino acid. These peptides are neither functionally nor structurally related to any known insect immune response peptides but show significant homology to microbicidal cationic peptides from mammalian granulocytes (defensins). We propose the name "insect defensins" for these insect antibiotic peptides.

Diptericins are 9 kDa inducible antibacterial peptides initially isolated from immune haemolymph of Phormia (Diptera). Following the isolation of a Drosophila cDNA encoding a diptericin homologue, we have now cloned a genomic fragment containing the Drosophila diptericin gene. To dissect the regulation of this gene, we have transformed flies with a fusion gene in which the reporter beta‐galactosidase gene is under the control of 2.2 kb upstream sequences of the diptericin gene. We show that such a fusion gene is inducible by injection of live bacteria or complete Freund's adjuvant and respects the tissue specific expression pattern of the resident diptericin gene. Our analysis reveals at least four distinct phases in the regulation of this gene: young larvae, late third instar larvae, pupae and adults. This complexity may be related to the presence in the upstream sequences of multiple copies of response elements previously characterized in genes encoding acute phase response proteins in mammals (e.g. NK‐kappa B, NF‐kappa B related, NF‐IL6 response elements).

Insect defensins are a family of 4‐kDa, cationic, inducible antibacterial peptides which bear six cysteine residues engaged in three intramolecular disulfide bridges. They owe their name to certain sequence similarities with defensins from mammalian neutrophiles and macrophages. We report the characterization of a novel defensin isoform from Drosophila and the cloning of the gene encoding a preprodefensin. The gene, which is intronless and present in a single copy/haploid genome, maps at position 46CD on the right arm of the second chromosome. The analysis of the upstream region of the gene reveals the presence of multiple putative cis‐regulatory sequences similar to mammalian regulatory motifs of acute‐phase‐response genes. Transcriptional profiles indicate that the Drosophila defensin gene is induced by bacterial challenge with acute‐phase kinetics. It is also expressed in the absence of immune challenge during metamorphosis. These and other data on the Drosophila defensin gene lead us to suggest that insect and mammalian defensins have evolved independently.

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Injury or injection of live bacteria into third instar larvae of the dipteran insect Phormia terranovae results in the appearance in the haemolymph of at least five groups of heat-stable, more or less basic peptides with antibacterial activity against Escherichia coli. Three of these peptides have been purified. The amino acid sequence has been completely established for one of these and partially (first 40 residues from the N-terminus) for the two others. The sequences show marked homologies indicating that the three peptides belong to a common family. They are not related to other known antibacterial peptides from insects [lysozymes, cecropins (including sarcotoxin I) and attacins]. We propose the name of diptericins for this new family of antibiotic molecules.It is now well established that lepidopteran and dipteran insects respond to a bacterial challenge and also to injury by synthesizing peptides with antibacterial activity (reviewed in Boman and Gotz [l]). Several antibacterial molecules induced in Hyalophora cecropia have been fully or partially characterized : these are the cecropins (3 -5 kDa basic, heatstable peptides) [2], the attacins (20 kDa basic or acidic proteins) [3] and lysozymes [4]. In dipterans, only one induced antibacterial protein has been characterized so far; it is a basic 39-residue molecule named sarcotoxin I, isolated from the blood of injured flesh-fly larvae Sarcophaga peregrina; this molecule shares significant homology with cecropins and is found in at least three forms [5].In the course of an investigation into the cellular and humoral defence reactions of the dipteran Phormia terranovae, a species closely related to Calliphora erythrocephala, we have recently obtained evidence for the appearance in the haemolymph of immunized larvae of a number of heat-stable, basic antibacterial proteins [6, 71. There are at least five of these proteins (or groups of proteins) in the immune haemolymph; none of them corresponds to lysozyme.In the present paper we show that three of these proteins belong to a novel class of antibacterial peptides; in particular, they differ from cecropins, attacins and lysozymes. We propose that they should be named diptericins. We report how, starting with immune plasma of Phormia, we have isolated the induced protein which shows the highest antibacterial activity on Escherichia coli in our assay conditions. It is a basic molecule (PI = 8.5) containing 82 amino acid residues with a relative molecular mass of 8610. We have determined the complete amino acid sequence of this major form (diptericin A) and sufficient N-terminal sequence of two of the minor forms (diptericins B and C) to reveal that there is a family of diptericins of related structure.