title: Eicosanoids mediate the laminarin-induced nodulation response in larvae of the flesh fly, Neobellieria bullata.
abstract: Insects have a highly developed innate immune system, including humoral and cellular components. The cellular immune responses refer to hemocyte-mediated processes such as phagocytosis, nodulation, and encapsulation. Nodulation is considered the predominant defense reaction to infection in insects. Treating third instar larvae of the grey flesh fly, Neobellieria bullata, with laminarin (beta-1,3-glucan, a typical component of fungal cell walls) induced nodulation in a dose-dependent manner. This reaction was initiated very soon after injection and reached its maximal response level after 4 h. The nodules were not randomly distributed in the hemocoel, but were concentrated around the crop. The possible role of eicosanoids in this nodulation process was determined by treating larvae with the phospholipase A(2) inhibitor, dexamethasone, the cyclooxygenase inhibitor, naproxen, and the lipoxygenase inhibitor, esculetin. Both dexamethasone and naproxen significantly impaired the ability of N. bullata larvae to form nodules in response to laminarin. Supplying dexamethasone-treated larvae with the eicosanoid precursor, arachidonic acid, restored the full response. On the other hand, treating larvae with esculetin did not influence the formation of nodules in response to laminarin. This is the first study that demonstrates the occurrence of a laminarin-induced nodulation response in Diptera. Phospholipase A(2) and cyclooxygenase activities, both involved in prostaglandin biosynthesis, appear to play an important role in the regulation of this process.
authors.affiliation: Laboratory of Developmental Physiology, Genomics and Proteomics, Department of Animal Physiology and Neurobiology, Zoological Institute, K.U. Leuven, Naamsestraat 59, B-3000 Leuven, Belgium.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Franssens
authors.forename: Gert
authors.initials: G
authors.lastname: Simonet
authors.forename: Annelies
authors.initials: A
authors.lastname: Bronckaers
authors.forename: Ilse
authors.initials: I
authors.lastname: Claeys
authors.forename: Arnold
authors.initials: A
authors.lastname: De Loof
authors.forename: Jozef
authors.initials: J
authors.lastname: Vanden Broeck
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D001413:Bacillus thuringiensis; D003907:Dexamethasone / Q000494:pharmacology; D004175:Diptera / Q000276:immunology* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015777:Eicosanoids / Q000096:biosynthesis / Q000378:metabolism*; D004926:Escherichia coli; D005936:Glucans; D007113:Immunity, Innate / Q000187:drug effects*; D007814:Larva / Q000187:drug effects / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D008853:Microscopy; D009288:Naproxen / Q000494:pharmacology; D011134:Polysaccharides / Q000494:pharmacology; D012441:Saccharomyces cerevisiae; D014468:Umbelliferones / Q000494:pharmacology
chemical_list: D015777:Eicosanoids; D005936:Glucans; D011134:Polysaccharides; D014468:Umbelliferones; D016718:Arachidonic Acid; D009288:Naproxen; D003907:Dexamethasone; C008247:laminaran; C007628:esculetin