The Antimicrobial Host Defense of Drosophila

Abstract

It has long been known that insects are particularly resistant to bacteria. Early workers in the late 19th century attributed this resistance to phagocytosis and to encapsulation by hemocytes (Kowalevsky 1887; Cuénot 1896). Around 1920, a number of independent studies established that insects could be protected against the injection of lethal doses of bacteria by the prior administration of low doses (Metalnikow 1920; Paillot 1920; Glaser 1918) and that this induced protection was correlated to the appearance of a potent antibacterial activity in the cell-free hemolymph. These studies, and most of the subsequent investigations in the field of insect immunity, were performed on large-sized insect species. It was only in 1972 that the problem of the inducible antibacterial activity was addressed in the small-sized Drosophila. Studies by Boman and associates (Boman et al. 1972) demonstrated that in Drosophila, as in other larger insect species, a primary infection can induce a protection against a secondary infection which otherwise would be lethal. In spite of the obvious interest of Drosophila as a model system, Boman and associates turned to the large pupae of the Cecropia moth for the first isolation of induced antibacterial molecules (cecropins; Steiner et al. 1981; attacins; Hultmark et al. 1983). Other groups subsequently worked on large-sized fly species, such as Sarcophaga peregrina (Okada and Natori 1985; Ando and Natori 1988; Matsuyama and Natori 1988) and Phormia terranovae (Dimarcq et al. 1988; Lambert et al. 1989). In the mid-eighties, two independent studies confirmed that Drosophila responds to the inoculation of bacteria within a few hours by the de novo synthesis of several peptides/polypeptides, some of which were presumed to be homologous to cecropins and attacins (Robertson and Postlethwait 1986; Flyg et al. 1987).