Nodulation is the predominant cellular defense reaction to bacterial challenge in insects. Eicosanoids mediate several steps in the nodulation process, including formation of hemocyte microaggregations. Isolated hemocyte preparations synthesize and secrete eicosanoids which mediate hemocyte immune reactions. Two major groups of eicosanoids are prostaglandins (products of cyclooxygenase pathways) and various products of lipoxygenase pathways. The goal of this study was to test the hypothesis that prostaglandins, but not lipoxygenase products, mediate hemocyte microaggregation reactions in response to bacterial challenge. The results indicate that isolated hemocyte preparations pretreated with the phospholipase A2 inhibitor, dexamethasone, and the cyclooxygenase inhibitors indomethacin and naproxen, yield fewer microaggregates than untreated control groups. Moreover, these inhibitors influence the formation of hemocyte microaggregations in a dose-dependent manner. The lipoxygenase inhibitors esculetin and caffeic acid did not impact the formation of microaggregates in this system. Furthermore, the influence of dexamethasone was reversed by amending experimental (dexamethasone-treated) preparations with prostaglandin H2, but not prostaglandin D2, prostaglandin E2, nor 5S-hydroperoxy-6E,8Z,11Z,14Z-eicosatetraenoic acid, a product of the lipoxygenase pathway. The study supports the hypothesis that prostaglandins are the primary mediators of microaggregation reactions to bacterial challenge in insect hemocyte preparations.
Species 1: Lepidoptera Sphingidae Manduca sexta (Tobacco Hornworm)
Keywords: immunity, eicosanoids
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