Susceptibility ofBrugia malayiandOnchocerca lienalismicrofilariae to nitric oxide and hydrogen peroxide in cell-free culture and from IFNγ-activated macrophages

Abstract

SUMMARYThe susceptibility ofBrugia malayiandOnchocerca lienalismicrofilariae to H2O2and NO either in cell-free culture or from IFNγ-activated macrophages was examined. In cell-free culture,O. lienalismicrofilariae were highly susceptible to H2O2induced toxicity, exhibiting rapid reductions in motility and viability. The addition of exogenous catalase abrogated H2O2-induced killing. In contrast,B. malayimicrofilariae were relatively resistant to H2O2, 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 withB. malayiand activated macrophages, inhibition of these effects was achieved by the addition of eitherL-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 thatB. malayiandO. lienalismicrofilariae have different susceptibility to H2O2, but are equally affected by exposure to NO. Moreover both species are killed by IFNγ-activated macrophages and in the case ofB. malayi, killing is dependent on the generation of NO via TNFα.