Biochemical pathway of melanotic encapsulation of Brugia malayi in the mosquito, Armigeres subalbatus

Abstract

The mosquito, Armigeres subalbatus, is naturally resistant to the filarial worm, Brugia malayi, and microfilariae (mf) penetrating the midgut are killed by melanotic encapsulation reactions in the hemocoel within 48 h following ingestion. This vector-parasite system was used to assess changes in hemolymph tyrosine, tyrosine derivatives, and catecholamine-metabolizing enzyme activities using high pressure liquid chromatography with electrochemical detection (HPLC-ED) during melanotic encapsulation reactions against mf. Tyrosine and dopa were detected in the hemolymph of both control and immune-activated (mf-exposed) mosquitoes, but not dopamine or N-acetyl dopamine (NADA). Tyrosine was significantly increased in immune-activated mosquitoes at 6 and 12 h post blood feeding, but was depleted following intrathoracic inoculation of mf in the absence of a blood meal. Dopa also was elevated in immune-activated mosquitoes at 6, 12, and 24 h post-exposure to mf. There were significant increases in phenol oxidase (PO) and dopa decarboxylase (DDC) activities in immune-activated mosquitoes as compared to controls, and these elevated activities were correlated with changes in tyrosine and dopa levels in the hemolymph. No significant differences in N-acetyl transferase (NAT) and dopachrome conversion enzyme (DCE) activities between control and immune-activated mosquitoes were observed. The possible roles these molecules play in melanotic encapsulation reactions of A. subalbatus against mf are discussed.