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Effects of inhibitors of serine protease, phenoloxidase and dopa decarboxylase on the melanization of Dirofilaria immitis microfilariae with Armigeres subalbatus haemolymph in vitro

Published online by Cambridge University Press:  01 July 1997

C. T. LIU ,
R. F. HOU ,
M. ASHIDA  and
C. C. CHEN
C. T. LIU
Affiliation:
Department of Parasitology, School of Medicine, National Yangming University, Shihpai, Taipei 112, Taiwan, Republic of China Department of Entomology, National Chung Hsing University, Taichung 402, Taiwan, Republic of China
R. F. HOU
Affiliation:
Department of Entomology, National Chung Hsing University, Taichung 402, Taiwan, Republic of China
M. ASHIDA
Affiliation:
Biochemical Laboratory, Institute of Low Temperature Science, Hokkaido University, Sapporo 060, Japan
C. C. CHEN
Affiliation:
Department of Parasitology, School of Medicine, National Yangming University, Shihpai, Taipei 112, Taiwan, Republic of China
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Abstract

The melanization of Dirofilaria immitis microfilariae in Armigeres subalbatus haemolymph in vitro is a two-step process. Firstly, the microfilariae are encased in a transparent capsule, then the capsule material is melanized later. Benzamidine HCl and p-amidinophenylmethanesulfonyl fluoride, both serine protease inhibitors, inhibited the deposition of the transparent capsule material and melanization. Diethyldithiocarbamate, a phenoloxidase inhibitor, did not prevent the deposition of the transparent capsule material but it did inhibit melanization. m-Hydroxybenzylhydrazine, a dopa decarboxylase inhibitor, had no inhibitory action on the deposition of the transparent capsule material. However, the time for the transparent capsule to become melanized was delayed due to the presence of m-hydroxybenzylhydrazine in the test system. Immunocytochemical localization showed that prophenoloxidase and/or phenoloxidase was present in the transparent capsule material. These results suggest (1) that prophenoloxidase cascade is essential in the melanization of microfilariae in mosquitoes and its putative activation behaviour is similar to that of other insects and (2) that the deposition of transparent capsule material is a result of the activation of prophenoloxidase by serine proteases and the melanization of the transparent capsule material is due to the presence of active phenoloxidase in capsule.

Keywords

Armigeres subalbatusDirofilaria immitisprophenoloxidasedopa decarboxylaseinhibitormelanization
Type
Research Article
Information
Parasitology , Volume 115 , Issue 1 , July 1997 , pp. 57 - 68
Copyright
1997 Cambridge University Press

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