Submitted to: Journal of Innate Immunity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/18/2008
Publication Date: 3/27/2009
Citation: Stanley, D.W., Miller, J., Tunaz, H. 2009. Eicosanoid Actions in Insect Immunity. Journal of Innate Immunity. 1:287-290. Interpretive Summary: The concept of biological control of insects is based on the idea that direct application of some of these pathogens and parasites can reduce pest insect populations and the economic damage due to pest insects. The problem, however, is the efficiency of these organisms in biological control programs is limited by insect immune defense reactions to challenge. One approach to improving the efficiency of biocontrol agents would be to somehow disable insect immune reactions to viral, bacterial, fungal and parasitic infections. We have discovered one group of molecules that mediate insect cellular immune reactions. We also found that some common, over-the-counter, pain relievers such as aspirin, block the production of these molecules during infection in insects. In this paper we present a background description of insect immunity and discuss the roles of the molecules we discovered in mediating insect immune reactions to infection. In doing so, we join two disparate concepts in insect science: one is research designed to understand how chemical mediators act in cellular immunity. The other is research designed to understand how chemical treatments can disable insect immunity. This new conjunction will be directly useful to scientists who are working to improve the efficacy of biological control methods. The ensuing improved biological control methods enhance long-term environmental and agricultural sustainability. These enhancements will benefit agricultural producers and the people who consume their products.
Technical Abstract: Insects express three lines of protection from infections and invasions. Their cuticles and peritrophic membranes are physical barriers. Infections and invasions are quickly recognized within insect bodies; recognition launches two lines of innate immune reactions. Humoral reactions involve induced synthesis of antimicrobial peptides, the bacteriolytic enzyme lysozyme and activation of the prophenoloxidase system. Cellular immune reactions include phagocytosis, nodulation and encapsulation. These reactions entail direct interactions between circulating hemocytes and the invaders. Antimicrobial peptides typically appear in the hemolymph some hours after infection and cellular immune reactions begin immediately an invasion is detected. Microaggregation is a step in the nodulation process, which is responsible for clearing the bulk of bacterial infections from circulation. Coordinated cellular actions lead to encapsulation of invaders, such as parasitoid eggs, that are very much larger than individual hemocytes. In this paper we review the roles of eicosanoids as crucial mediators of insect immune reactions, particularly cellular reactions. We briefly describe insect immune functions, outline eicosanoid biosynthesis and treat eicosanoid actions in cellular immunity of insects. Eicosanoids act in several cellular defense functions, including microaggregation, nodulation, encapsulation, cell spreading and hemocyte migration toward a source of the bacterial peptide fMLP. We also describe our most recent work on the influence of one group of eicosanoids, prostaglandins, on gene expression in an established insect cell line.