EICOSANOIDS MEDIATE NODULATION RESPONSES TO BACTERIAL-INFECTIONS IN LARVAE OF THE SILKMOTH, BOMBYX-MORI

1) Nodulation is the first, and qualitatively predominant, cellular de fense reaction to bacterial infections in insects and other invertebra tes; 2) treating silkworms, Bombyx mori, with the eicosanoid biosynthe sis inhibitor, dexamethasone, strongly reduced nodulation responses to bacterial infections; 3) the influence of dexamethasone was reversed oy injecting the eicosanoid-precursor polyunsaturated ratty acid, arac hidonic acid (20:4n-6), into dexamethasone-treated, infected larvae; 4 ) the presence of an eicosanoid biosynthesis system in silkworms was d ocumented. Demonstrated elements include a digestive phospholipase Az, incorporation of exogenous 20:4n-6 into fat body phospholipids, the p resence of 20:4n-6 in cellular phospholipids, a fat body intracellular phospholipase A? that can hydrolyze 20:4n-6 from cellular phospolipid s, and eicosanoid biosynthetic enzymes; and) these findings support th e hypothesis that eicosanoids mediate cellular immune responses to bac terial infections in silkworms. (C) 1997 Elsevier Science Inc.