Ultrastructural Localization of Phenoloxidase in the Midgut of Refractory Anopheles gambiae and Association of the Enzyme with Encapsulated Plasmodium cynomolgi

A melanogenic enzyme, phenoloxidase, was localized ultrastructurally in the midgut epithelia of 2 strains of Anopheles gambiae, a refractory strain that melanotically encapsulates Plasmodium cynomolgi ookinetes on the midgut, and a susceptible strain that does not. Midguts were incubated with either...

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Bibliographic Details
Published in:The Journal of parasitology 1989-08, Vol.75 (4), p.594-600
Main Authors: Paskewitz, Susan M., Brown, Mark R., Collins, Frank H., Lea, Arden O.
Format: Article
Language:English
Subjects:
Animals
Anopheles - enzymology
Anopheles - parasitology
Anopheles - ultrastructure
Biological and medical sciences
Blood
Capsules
Catechol Oxidase - metabolism
Digestive System - enzymology
Digestive System - ultrastructure
Encapsulating
Enzymes
Fundamental and applied biological sciences. Psychology
Histocytochemistry
Insecta
Invertebrates
Labyrinths
Melanin
Microscopy, Electron
Midgut
Monophenol Monooxygenase - metabolism
Morphology. Histology. Cytology
Mosquitos
Parasites
Pathogenesis and Host Response
Plasmodium - growth & development
Reaction products
Species Specificity
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Summary:A melanogenic enzyme, phenoloxidase, was localized ultrastructurally in the midgut epithelia of 2 strains of Anopheles gambiae, a refractory strain that melanotically encapsulates Plasmodium cynomolgi ookinetes on the midgut, and a susceptible strain that does not. Midguts were incubated with either dopa or dopamine, and the resultant electron-dense product of phenoloxidase activity was localized on the basal lamina (BL) and cellular basal membrane labyrinth (BML) in uninfected mosquitoes of both strains. In infected refractory mosquitoes, the reaction products still were observed on the BL and BML but were especially dense in the BML of midgut cells near encapsulated ookinetes and in the capsule itself. In infected susceptible mosquitoes, phenoloxidase localization was reduced or absent in the BL and BML and was not observed near parasites. Phenylthiourea (PTU) inhibited the phenoloxidase reaction, indicating that the reaction product deposited in the absence of PTU resulted from enzyme activity and not autooxidation of the substrates. It is concluded that higher levels of phenoloxidase in the refractory strain following a blood meal may contribute to the ability to encapsulate ookinetes.
ISSN:0022-3395
1937-2345
DOI:10.2307/3282911