Induction and localization of FAD-glucose dehydrogenase (GLD) during encapsulation of abiotic implants in Manduca sexta larvae

FAD-Glucose dehydrogenase (GLD) (EC 1.1.99.10) was assayed during the encapsulation response against abiotic implants (sterile latex) in fourth instar Manduca sexta larvae. No GLD activity was detected in fresh hemolymph or hemocytes of control or sham-treated larvae. Two types of responses occurred at 0.5 and 3 h after implantation. In the majority of larvae, only the encapsulation had high levels of GLD specific activity. In the second response, low levels of GLD specific activity were detected in hemocytes and cell-free hemolymph but not in the encapsulation. By 24 h after implantation, GLD activity was detected in the encapsulation tissue of all larvae. Levels of GLD specific activity did not significantly differ over time (0.5-72 h) during encapsulation. Freezing cell-free hemolymph from control larvae activated otherwise inactive hemolymph stores of GLD. In vitro experiments and histochemical staining demonstrated that GLD activity was localized in granules of plasmatocytes adhered to coverslips. Granules of both plasmatocytes and granulocytes contained GLD protein as detected by immunohistochemistry. Based on previous characterization of GLD, we hypothesize that GLD participates in strengthening the encapsulation and in the killing reaction, via reaction with quinones generated by phenoloxidase and subsequent production of free radicals.