Eicosanoids mediate nodulation responses to bacterial infections in larvae of the silkmoth, Bombyx mori

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