Phospholipase A2 is secreted by cercaria of Schistosoma mansoni
Cardoso LS; Rocha FF, Rumjanek FD and Atella GC
Instituto de Bioquímica Médica, Centro de Ciências da Saúde - Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ. lcardoso@bioqmed.ufrj.br
Schistosomiasis is infectious disease caused by trematode flatworms of the genus Schistosoma. There are three major species of Schistosoma. Schistosoma mansoni, a major species in Africa and South America, was used as a model in this study. The initial infection of the human host by schistosome involves skin penetration by a multicelullar larva called cercaria. These larvae secrete different proteins that make possible the penetration, degrading the dermis cells, and also play an essential role by avoiding response from the host’s immunological system. Phospholipases A2 (PLA2) are enzymes responsible for hydrolyzing phospholipids yielding lysophospholipids and fatty acids. In this work we investigated the presence of a PLA2 in cercaria and its secretions.
Cercarias were “shed” from their host snails in glass culture dishes. Cercarias were then removed from the supernatant by centrifugation at 3000 rpm. The centrifugation step separates the cercarias (pellet) and the supernatant composed by the production of cercarial secretions. Both were assayed using PED6, a fluorogenic substrate for PLA2. After incubation, media were collected and subjected to lipid extraction and thin-layer chromatography, followed by scanning on a Storm 860 laser scanner and quantification of fluorescent fatty acid. PLA2 activity was detected in both preparations, but the activity was 80% higher in cercaria secretion than pellet. The effect of calcium on enzyme activity was determined by incubations of pellet and supernatant in the presence of calcium and EGTA. The biggest activity was observed in sample with calcium while, in the sample with EGTA, the activity of PLA2 reduced until approximately 95%.
This study demonstrates for the first time that cercaria synthesize a PLA2 and release it into the culture medium, this molecule may play a role in the parasite invasion on human skin.
Supported by CNPq, FAPERJ, IFS
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