Inhibition of carbohydrate uptake of Onchocerca volvulus infective larvae (L3) by effector cell constituents

Abstract

The in vitro killing of Onchocerca volvulus infective third stage larvae (L3) by components of their human hosts' defence mechanisms is not well documented, as no suitable assay exists. Motility is inappropriate as a criterion of larval viability because of the unsteady winding movements of L3. In the present study, a metabolic parameter for larval viability, the uptake of [³H]2-deoxy-D-glucose, was evaluated. To demonstrate the reproducibility and validity of this test, the oxygen radical hydrogen peroxide (H₂O₂) was applied to viable L3 and the death of L3 demonstrated by a 90% reduction in glucose uptake. The incorporation of glucose by the filarial larvae was also determined after in vitro exposure to lysates of the putative effector cells, i.e. eosinophilic and neutrophilic granulocytes and monocytes. Effector-cell-derived components led to a 30–80% dose-dependent decrease in deoxy-glucose uptake, with a half-maximal effect at about 500 µg ml⁻¹. These experiments demonstrate, for the first time, the deleterious impact of effector cell constituents on the metabolic activity of O. volvulus L3. The assay could be used to evaluate the effect of distinct natural or recombinant effector molecules on the viability of O. volvulus infective larvae and to investigate the effect of parasite molecules which interfere with effector mechanisms.