BIOCHEMICAL PATHWAY OF MELANOTIC ENCAPSULATION OF BRUGIA-MALAYI IN THE MOSQUITO, ARMIGERES SUBALBATUS

The mosquito, Armigeres subalbatus, is naturally resistant to the fila rial worm, Brugia malayi, and microfilariae (mf) penetrating the midgu t are killed by melanotic encapsulation reactions in the hemocoel with in 48 h following ingestion. This vector-parasite system was used to a ssess changes in hemolymph tyrosine, tyrosine derivatives, and catecho lamine-metabolizing enzyme activities using high pressure liquid chrom atography with electrochemical detection (HPLC-ED) during melanotic en capsulation reactions against mf. Tyrosine and dopa were detected in t he hemolymph of both control and immune-activated (mf-exposed) mosquit oes, but not dopamine or N-acetyl dopamine (NADA). Tyrosine was signif icantly increased in immune-activated mosquitoes at 6 and 12 h post bl ood feeding, but was depleted following intrathoracic inoculation of m f in the absence of a blood meal. Dopa also was elevated in immune-act ivated mosquitoes at 6, 12, and 24 h post-exposure to mf. There were s ignificant increases in phenol oxidase (PO) and dopa decarboxylase (DD C) 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-ace tyl transferase (NAT) and dopachrome conversion enzyme (DCE) activitie s between control and immune-activated mosquitoes were observed. The p ossible roles these molecules play in melanotic encapsulation reaction s of A. subalbatus against mf are discussed.