Mediation of inducible nitric oxide and immune-reactive lysozymes biosynthesis by eicosanoid and biogenic amines in flesh flies

Abstract Nitric oxide (NO) plays various roles in insect immunity: as a cytotoxic component and as a signalling molecule; and immune-reactive lysozymes (IrLys) provide a first line of humoral immune functions against invading bacteria. Although there is considerable literature on eicosanoid and biogenic monoamine actions on insect immunity, there is no information on the role(s) of these chemicals in inducing NO and IrLys. We addressed this gap by challenging third instar Sarcophaga (Liopygia) argyrostoma (Robineau-Desvoidy) with the Gram-positive bacterium Micrococcus luteus. Here, we report that bacterial challenge induces elevation of NO and IrLys concentrations in haemocytes and in the fat body. The plasma pool content is comparatively low. Eicosanoid biosynthesis inhibitors (EBIs) lead to suppression of both NO and IrLys levels. Control larvae have low constitutive levels of NO and lysozyme concentrations. Octopamine (OA) elicits elevation of NO and IrLys concentrations. A similar effect is obtained by 5-hydroxytryptamine (5- HT) for NO. These data indicate immune-mediating roles of eicosanoids, OA and 5-HT in NO and IrLys activities.Larval filth-breeding flies like the flesh fly Sarcophaga argyrostoma (Robineau-Desvoidy) (Diptera: Sarcophagidae) live in highly bacteria-contaminated habitats and are constantly exposed to infection. We hypothesized that flesh flies express NO and lysozymes in response to bacterial-challenge and that eicosanoids and biogenic monoamines (BMAs) mediate these responses. In this paper, we investigate the roles of eicosanoids, using eicosanoid biosynthesis inhibitors (EBIs) and BMAs as mediators of NO and lysozyme biosynthesis