EICOSANOIDS MEDIATE CELLULAR IMMUNE RESPONSE AND PHENOLOXIDASE REACTION TO VIRAL INFECTION IN ADULT Pimpla turionellae

Abstract

Nodulation is the predominant insect cellular immune response to microbial infections. We posed the hypothesis that parasitoid insects in their adulthood express melanotic nodulation reactions to viral challenge and that eicosanoids mediate nodulation reactions and phenoloxidase (PO) activation in response to viral challenge. To test this idea, we injected Pimpla turionellae adults with indomethacin, a nonsteroidal anti-inflammatory drug, immediately prior to intrahemocoelic injection of Bovine herpes simplex virus-1 (BHSV-1). Treating newly emerged adults of P. turionellae with BHSV-1 induced nodulation reactions, and decreased PO activity at high viral doses. Relative to vehicle-treated controls, indomethacin-treated adults produced significantly reduced numbers of nodules following viral infection (down from approximately 21 nodules per adult to less than six nodules per adult). In addition to injection treatments, increasing dietary indomethacin dosages (from 0.01% to 0.1%) were associated with decreasing nodulation (by six-fold) and PO (by about three-fold) reactions to BHSV-1 injection. Wasp adults orally fed with the lowest dietary indomethacin concentration (0.001%) expressed significantly increased PO activity (1.45 unit/min/mg protein) while nodulation reaction was not affected in response to viral challenge compared to control adults. We infer from these findings that cyclooxygenase (COX) products, at least prostaglandins, mediate nodulation response and PO action to viral infection in adults of these highly specialized insects.