Studies on phospholipid turnover argue against sloughing of tegumental membranes in adult Schistosoma mansoni

The tegumental membrane complex of Schistosoma mansoni is the site of inter action between the parasite and the host. The tegument is involved in uptak e of many nutrients, but also plays a crucial role in the evasion of the ac tions of the host immune system. Essential for the success of this evasion is maintaining the integrity of the tegumental membranes. The rate of turno ver of phospholipids was investigated by pulse-labelling worms cultured in vitro, followed by additional incubation in the presence of unlabelled subs trates. Tegumental membranes were isolated, characterized using antibodies against specific tegumental proteins, and analysed. It was demonstrated tha t the most prominent fatty acid found in tegumental phospholipids, palmitat e, incorporated rapidly into the phospholipid fraction during a 30 min puls e labelling. In a subsequent 20 h chase with unlabelled substrates, the inc orporated radioactivity was lost again from the tegumental membrane complex . This high turnover of palmitate was found to be limited to phosphatidylch oline (PC) only. The turnover was due to deacylation/reacylation, and not t o the sloughing of membranes as is the case in schistosomula. It is specula ted that this rapid turnover of PC in the tegument of adult schistosomes pl ays a new and important role in the immune evasion by the parasite.