Role of a Galactose-Binding Insect Lectin in Defense Response (s) Against Invading Pathogens

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The purpose of the proposed research is further to elucidate the role of insect lectins in the defense response against pathogens. A galactose binding lectin from Spodoptera exigua (beet armyworm) will be used in these studies. This lectin is easily extracted from larval hemolymph and has been shown to opsonize potential fungal pathogens which have surface galactose residues. Monoclonal antibodies against the lectin will be prepared in order to localize the molecule in insect tissues. Light and electron microscopy will be used for these studies and in experiments using direct probes to localize lectin receptors on cell walls of selected microorganisms. Antimicrobial properties of the lectin will be assessed as well as the fate of opsonized microbes phagocytosed by host granulocytes. Viability of ingested cells will be determined by conventional plating methods and by use of a methylene blue staining assay. Finally, the distribution of lectin receptors on both immunocompetent and immunosuppressed granulocytes will be examined. Lectins are specific sugar-binding proteins that have been detected in the body fluids of numerous animal species. Although little is known about the function of these molecules, it has been suggested on the basis of a variety of sketchy evidence that in insects they may function in defense against bacteria or fungi by coating the microorganisms and promoting their removal by scavenger cells in the insect's blood. This research will examine this hypothesis more thoroughly and should elucidate the role(s) of lectins in an insect's defense against invading microorganisms.