Abstract
Insects, like all invertebrates, express robust innate, but not adaptive, immune reactions to infection and invasion. Insect immunity is usually resolved into three major components. The integument serves as a physical barrier to infections. Within the hemocoel, the circulating hemocytes are the temporal first line of defense, responsible for clearing the majority of infecting bacterial cells from circulation. Specific cellular defenses include phagocytosis, microaggregation of hemocytes with adhering bacteria, nodulation and encapsulation. Infections also stimulate the humoral component of immunity, which involves the induced expression of genes encoding antimicrobial peptides and activation of prophenoloxidase. These peptides appear in the hemolymph of challenged insects 6–12 hours after the challenge. Prostaglandins and other eicosanoids are crucial mediators of innate immune responses. Eicosanoid biosynthesis is stimulated by infection in insects. Inhibition of eicosanoid biosynthesis lethally renders experimental insects unable to clear bacterial infection from hemolymph. Eicosanoids mediate specific cell actions, including phagocytosis, microaggregation, nodulation, hemocyte migration, hemocyte spreading and the release of prophenoloxidase from oenocytoids. Some invaders have evolved mechanisms to suppress insect immunity; a few of them suppress immunity by targeting the first step in the eicosanoid biosynthesis pathways, the enzyme phospholipase A2. We proposed research designed to cripple insect immunity as a technology to improve biological control of insects. We used dsRNA to silence insect genes encoding phospholipase A2, and thereby inhibited the nodulation reaction to infection. The purpose of this article is to place our view of applying dsRNA technologies into the context of eicosanoid actions in insect immunity. The long-term significance of research in this area lies in developing new pest management technologies to contribute to food security in a world with a rapidly growing human population.
Highlights
Insects and other invertebrates have been used a model systems since of the beginning of immunological research
The pioneering work on the roles of eicosanoids in insect immunity revealed that pharmaceutical inhibitors of eicosanoid biosynthesis lethally impaired clearance of injected bacteria from hemolymph circulation [21], with only speculation on what the eicosanoids do
We showed that challenging late instar Tribolium castaneum with the bacterium E. coli evoked nodulation in a time- and bacterial dose-related manner
Summary
Insects and other invertebrates have been used a model systems since of the beginning of immunological research. Elie Metchnikoff, born in Kharkov, Russia, was an embryologist who became fascinated with what he called phagocytes He studied phagocytes, first as an embryological study; his seminal observation with respect to animal immunology came in 1882, after he moved from Russia to Messina, Italy. First as an embryological study; his seminal observation with respect to animal immunology came in 1882, after he moved from Russia to Messina, Italy He placed a splinter into the transparent body of a starfish, the bipinnaria larval stage, observed phagocytes surrounding the splinter. The recent advent of gene silencing tools opens the possibility of applying knowledge of eicosanoid signaling to insect pest control technologies In this brief paper we sketch insect immunity, outline eicosanoid systems and review the roles of eicosanoids as crucial mediators of insect immune functions. We report on our efforts to cripple pest insect immunity using molecular tools
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