Demonstration and partial characterization of a tegument associated capping response on adult male Schistosoma mansoni

Abstract

The tegumental surface of the adult schistosome functions as the primary interface between the parasite and its host. Lateral redistribution of antigens on the tegumental surfaces of adult male Schistosoma mansoni due to the binding of ligands was examined. Ligand induced lateral redistribution resulted in an anatomical and physiological phenomenon reminiscent of cellular capping. Parasites were observed to cap absorbed host antigens (mouse IgG) and tegumental components containing sugar moieties (alpha-D-glucose and/or alpha-D-mannose) upon the addition of colloidal gold labeled goat anti-mouse IgG or colloidal gold concanavalin A, respectively. A highly ordered lateral displacement of both probes was observed over a time span of 8-10 minutes, culminating in a concentrated cap on the apex of dorsal anterior and posterior tubercles. The ligands which induced the formation of the caps were ultimately expelled from the parasite. Capping in schistosomes was determined to be similar to cellular capping in that both processes were temperature sensitive, Ca[^2+]-calmodulin dependent, and triggered an influx of Ca[^2+] during the process. The utilization of inhibitory drugs to block capping suggests that schistosome capping, as in unicellular capping, is a microtubular and microfilament dependent process. Schistosome tegument capping differed from uni-cellular capping in that, under normal conditions, patching was not observed; numerous caps were formed per parasite and not all ligands binding to the surface induced capping. Alternatively, exposure to parasite antigen specific antibodies resulted in minimal binding of these antibodies and no capping. Calcium influx during anti-parasite antibody exposure was noted at the onset of the assay, but quickly returned to baseline levels. Additionally, the effects of the anthelmintic drug praziquantel (PZQ) on antibody induced capping and calcium influx were investigated. Parasites exposed to anti-host or anti-parasite antibodies and praziquantel displayed accelerated capping, an inhibition of cap expulsion and a radical increase in calcium uptake. These results indicated that PZQ's efficacy may, in part, be predicated upon interference with the parasite's ability to control immunological events occurring at the host-parasite interface.