EICOSANOIDS MEDIATE MICROAGGREGATION AND NODULATION RESPONSES TO BACTERIAL-INFECTIONS IN BLACK CUTWORMS, AGROTIS-IPSILON, AND TRUE ARMYWORMS, PSEUDALETIA-UNIPUNCTA

Nodulation is the first, and quantitatively predominant, cellular defe nse reaction to bacterial infection in insects and other invertebrates , Inhibition of eicosanoid biosynthesis in true army-worms, Pseudaleti a unipuncta, and black cutworms, Agrotis ipsilon, immediately prior to intrahemocoelic injections with heat-killed preparations of the bacte rium, Serratia marcescens, severely impaired the nodulation response. Five eicosanoid biosynthesis inhibitors, including dexamethasone (a ph ospholipase A(2) inhibitor), indomethacin, ibuprofen (cyclooxygenase i nhibitors), phenidone (dual lipoxygenase/cyclooxygenase inhibitor) and eicosatetraynoic acid (an arachidonic acid analog that inhibits all a rachidonic acid metabolism) severely reduced nodulation in infected in sects, The dexamethasone effects were reversed by treating true army-w orms with arachidonic acid immediately after infection, In addition to these pharmacological findings, we demonstrate that an eicosanoid bio synthesis system is present in these insects, Arachidonic acid is pres ent in fat body phospholipids at about 0.4% of total phospholipid fatt y acids, Fat body expressed a phospholipase A(2) that can hydrolyze ar achidonic acid from the sn-2 position of cellular phospholipids, Fat b ody preparations were competent to biosynthesize prostaglandins, of wh ich PGE(2) was the major product. These findings support the hypothesi s that eicosanoids mediate cellular immune reactions in insects. (C) 1 997 Elsevier Science Ltd. All rights reserved.