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DW Stanley

Publications and source records attributed to DW Stanley.

4 recordsLinked to original sources
PubMed2000

Insect cellular reactions to the lipopolysaccharide component of the bacterium Serratia marcescens are mediated by eicosanoids.

Nodulation, which begins with the formation of cellular microaggregates, is the predominant cellular defense reaction to bacterial infections in insects. We suggested that these reactions to bacterial infections are mediated by eicosanoids. The lipopolysaccharide (LPS) component of some bacterial cells stimulates defense reactions in mammals and insects. Here, we report on experiments designed to test the hypothesis that eicosanoids mediate microaggregation reactions to LPS. Injections of LPS (purified from the bacterium, Serratia marcescens) into larvae of the tenebrionid beetle, Zophobas atratus, stimulated microaggregation reactions in a dose-dependent manner. Treatments with eicosanoid-biosynthesis inhibitors immediately prior to LPS challenge sharply reduced the microaggregation responses. Separate treatments with specific inhibitors of phospholipase A(2), cyclooxygenase and lipoxygenase reduced microaggregation, supporting our view that microaggregate formation involves lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent within 30min after injection, and microaggregation was significantly reduced, relative to control insects, over the following 90min. The dexamethasone effects were reversed by treating LPS-injected insects with the eicosanoid precursor, arachidonic acid. These findings indicate that cellular defense reactions to a specific component of bacterial cells are mediated by eicosanoids, and open up new possibilities for dissecting detailed hemocytic actions in insect immune reactions to bacterial infections.

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PubMed1999

Prostaglandin production in response to a bacterial infection in true armyworm larvae

Prostaglandin levels were determined by fluorometric HPLC analysis of hemolymph collected from larvae of the true armyworm, Pseudaletia unipuncta, that had been injected with bacteria. Prostaglandins were extracted and derivatized with the fluorogenic compound 9-anthryldiazomethane and detected by fluorescence-HPLC. One of the prostaglandins produced was identified as prostaglandin F(2alpha) based on HPLC retention time. The chemical identity of prostaglandin F(2alpha) was confirmed by isolation and derivatization followed by gas chromatography mass spectrometry analysis. Larvae injected with heat-killed bacteria, Serratia marcescens, produced about 4 times as much prostaglandin F(2alpha) as larvae injected with saline. In a separate experiment, larvae injected with bacteria and the prostaglandin precursor arachidonic acid produced still higher levels of prostaglandin F(2alpha). The production of prostaglandin was inhibited with phenidone, a dual cyclooxygenase and lipoxygenase inhibitor. These data indicate that bacterial injections stimulate increased eicosanoid biosynthesis in true armyworms, particularly biosynthesis of prostaglandin F(2alpha). Our findings add considerable support to the hypothesis that eicosanoids mediate insect cellular immune reactions to bacterial infections. Arch. Copyright 1999 Wiley-Liss, Inc.

Journal Article↗
PubMed1999

In vitro secretion of digestive phospholipase A(2) by midguts isolated from tobacco hornworms, manduca sexta

We report on secretion of phospholipase A(2) (PLA(2)) by in vitro preparations of midguts isolated from tobacco hornworms, Manduca sexta. This enzyme is responsible for hydrolysis of fatty acids from the sn-2 position of phospholipids, a necessary step in fatty acid absorption. The in vitro midgut preparations are competent to secrete PLA(2) into incubation buffer. Secretion began within the first 30 min of incubation and increased to a maximum at 8 h. We selected 2 h incubations because substantial loss of tissue integrity was observed after 8 h incubations. Using 2 h incubations, we recorded increased secretion of digestive PLA(2) from midguts incubated in buffer amended with diet or with yeast as a component of the diet. We also recorded small increases in secretion of PLA(2) from midguts incubated in buffer amended with a specific phospholipid, phosphatidylcholine. Midguts incubated in buffer amended with increased concentrations of phospholipid did not yield higher levels of PLA(2) activity. Lepidopteran midguts can be divided into three regions, and we recorded the highest secretion of PLA(2) from the middle region and lowest secretion from the anterior region. Because isolated midguts responded to food chemicals with increased secretion of digestive PLA(2), we suggest that secretion of digestive enzymes in tobacco hornworms is regulated by a prandial and/or paracrine mechanism, as suggested for digestive proteases in other insect species. Arch. Insect Biochem. Physiol. 42:179-187, 1999.Copyright 1999 Wiley-Liss, Inc.

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