Shedding of surface-bound antibody by adult Dictyocaulus viviparus

Dictyocaulus viviparus-infected calves exhibit strong antibody responses to the surface of all stages of the parasite. To examine whether surface-bound antibody is released, fluorescent-labelled antibody was bound to living parasites that were incubated either at 37 degrees C, or in the presence of a metabolic inhibitor at 2 degrees C. The amount of surface-bound antibody was measured by quantitative fluorescence before and after incubation for 24 h. Loss of antibody from the parasite surface was compared in adult worms, sheathed and artificially exsheathed third-stage larvae (L3). Rapid reductions in fluorescence were observed with adult parasites maintained at 37 degrees C but this was inhibited by incubation at 2 degrees C in the presence of sodium azide. In contrast, there was no such loss from the surface of the sheathed or exsheathed L3 maintained at 37 degrees C.