Susceptibility of Brugia malayi and Onchocerca lienalis microfilariae to nitric oxide and hydrogen peroxide in cell-free culture and from IFNγ-activated macrophages

The susceptibility of Brugia malay and Onchocerca lienalis microfilariae to H 2 O 2 and NO either in cell-free culture or from IFNγ-activated macrophages was examined. In cell-free culture, O. lienalis microfilariae were highly susceptible to H 2 O 2 induced toxicity, exhibiting rapid reductions in motility and viability. The addition of exogenous catalase abrogated H 2 O 2 -induced killing. In contrast, B. malayi microfilariae were relatively resistant to H 2 O 2 , with concentrations as high as 50 μM having no effect on motility or viability. On exposure to NO, both species showed reductions in motility within 5-30 min, but longer was required to see effects on the viability of microfilariae. Parasites incubated with IFNγ-activated macrophages also exhibited marked reductions in motility and viability. In cultures with B. malayi and activated macrophages, inhibition of these effects was achieved by the addition of either L-NMMA, to abolish NO production, or neutralizing anti-TNFα antibodies. Attempts to inhibit parasite killing by the addition of catalase to macrophage cultures were ineffective. The results of this study show that B. malayi and O. lienalis microfilariae have different susceptibility to H 2 O 2 , but are equally affected by exposure to NO. Moreover both species are killed by IFNγ-activated macrophages and in the case of B. malayi, killing is dependent on the generation of NO via TNFα.