EFFECTS OF INHIBITORS OF SERINE-PROTEASE, PHENOLOXIDASE AND DOPA DECARBOXYLASE ON THE MELANIZATION OF DIROFILARIA-IMMITIS MICROFILARIAE WITH ARMIGERES SUBALBATUS HEMOLYMPH IN-VITRO

The melanization of Dirofilaria immitis microfilariae in Armigeres sub albatus haemolymph in vitro is a two-step process. Firstly, the microf ilariae are encased in a transparent capsule, then the capsule materia l is melanized later. Benzamidine HCl and p-amidinophenylmethanesulfon yl fluoride, both serine protease inhibitors, inhibited the deposition of the transparent capsule material and melanization. Diethyldithioca rbamate, a phenoloxidase inhibitor, did not prevent the deposition of the transparent capsule material but it did inhibit melanization. m-Hy droxybenzylhydrazine, a dopa decarboxylase inhibitor, had no inhibitor y action on the deposition of the transparent capsule material. Howeve r, the time for the transparent capsule to become melanized was delaye d due to the presence of m-hydroxybenzylhydrazine in the test system. Immunocytochemical localization showed that prophenoloxidase and/or ph enoloxidase was present in the transparent capsule material. These res ults suggest (1) that prophenoloxidase cascade is essential in the mel anization of microfilariae in mosquitoes and its putative activation b ehaviour is similar to that of other insects and (2) that the depositi on of transparent capsule material is a result of the activation of pr ophenoloxidase by serine proteases and the melanization of the transpa rent capsule material is due to the presence of active phenoloxidase i n capsule.