Schistosomiasis, caused by parasitic helminths, remains a serious human disease in the tropics. Cercariae of Schistosoma mansoni infect their hosts by direct skin penetration, aided by secretions from acetabular and head glands. Both proteolytic and immunomodulatory properties have been ascribed to the released material, but to date only five isoforms of elastase and one putative anti-inflammatory protein (Sm16) have been cloned. We analyzed secretions from mechanically transformed cercariae by two-dimensional electrophoresis. An average gel image was created and compared with a separation of soluble larval extract, revealing a less complex spot pattern in the secretions with 60% of the spots matched to the larval extract. Subsequent tandem mass spectrometric analysis identified 48 spots from the released material, representing approximately 80% of its normalized volume. Twenty-nine of these are likely to originate in the vesicles, and 18 are likely to originate in the cytosol of the glands (the latter class being present due to holocrine secretion); one is unknown. The vesicular proteins were significantly more enriched than the cytosolic proteins in the released material when compared with the larval extract. A novel metalloproteinase (termed SmPepM8) was the second most abundant constituent after three isoforms of cercarial elastase. In addition, a dipeptidyl peptidase IV (SmDPP IV) was discovered but in much smaller quantity. A new serine protease inhibitor (SmSerp_c) was also prominent. Along with Sm16, four potential immunomodulators were identified, three with similarity to venom allergens (SmSCP_a, _b, and _c) and one with homology to the potassium channel blockers in scorpion venom (SmKK7). Interrogation of the expressed sequence tag database found transcripts encoding the majority of vesicular proteins present solely in the intramolluscan stages of the life cycle. Distinct patterns of radiolabel incorporation suggested three separate origins for the vesicular proteins. All the novel constituents merit investigation as vaccine candidates, and the potential immunomodulators merit investigation as therapeutic agents.

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The blood fluke Schistosoma mansoni can live for years in the hepatic portal system of its human host and so must possess very effective mechanisms of immune evasion. The key to understanding how these operate lies in defining the molecular organisation of the exposed parasite surface. The adult worm is covered by a syncytial tegument, bounded externally by a plasma membrane and overlain by a laminate secretion, the membranocalyx. In order to determine the protein composition of this surface, the membranes were detached using a freeze/thaw technique and enriched by sucrose density gradient centrifugation. The resulting preparation was sequentially extracted with three reagents of increasing solubilising power. The extracts were separated by 2-DE and their protein constituents were identified by MS/MS, yielding predominantly cytosolic, cytoskeletal and membrane-associated proteins, respectively. After extraction, the final pellet containing membrane-spanning proteins was processed by liquid chromatographic techniques before MS. Transporters for sugars, amino acids, ions and other solutes were found together with membrane enzymes and proteins concerned with membrane structure. The proteins identified were categorised by their function and putative location on the basis of their homology with annotated proteins in other organisms.

Schistosoma mansoni is a well-adapted blood-dwelling parasitic helminth, persisting for decades in its human host despite being continually exposed to potential immune attack. Here, we describe in detail micro-exon genes (MEG) in S. mansoni, some present in multiple copies, which represent a novel molecular system for creating protein variation through the alternate splicing of short (#36 bp) symmetric exons organized in tandem. Analysis of three closely related copies of one MEG family allowed us to trace several evolutionary events and propose a mechanism for micro-exon generation and diversification. Microarray experiments show that the majority of MEGs are up-regulated in life cycle stages associated with establishment in the mammalian host after skin penetration. Sequencing of RT-PCR products allowed the description of several alternate splice forms of micro-exon genes, highlighting the potential use of these transcripts to generate a complex pool of protein variants. We obtained direct evidence for the existence of such pools by proteomic analysis of secretions from migrating schistosomula and mature eggs. Whole-mount in situ hybridization and immunolocalization showed that MEG transcripts and proteins were restricted to glands or epithelia exposed to the external environment. The ability of schistosomes to produce a complex pool of variant proteins aligns them with the other major groups of blood parasites, but using a completely different mechanism. We believe that our data open a new chapter in the study of immune evasion by schistosomes, and their ability to generate variant proteins could represent a significant obstacle to vaccine development.

The intestinal helminth parasite, Heligmosomoides polygyrus offers a tractable experimental model for human hookworm infections such as Ancylostoma duodenale and veterinary parasites such as Haemonchus contortus. Parasite excretory-secretory (ES) products represent the major focus for immunological and biochemical analyses, and contain immunomodulatory molecules responsible for nematode immune evasion. In a proteomic analysis of adult H. polygyrus secretions (termed HES) matched to an extensive transcriptomic dataset, we identified 374 HES proteins by LC-MS/MS, which were distinct from those in somatic extract HEx, comprising 446 identified proteins, confirming selective export of ES proteins. The predominant secreted protein families were proteases (astacins and other metalloproteases, aspartic, cysteine and serine-type proteases), lysozymes, apyrases and acetylcholinesterases. The most abundant products were members of the highly divergent venom allergen-like (VAL) family, related to Ancylostoma secreted protein (ASP); 25 homologues were identified, with VAL-1 and -2 also shown to be associated with the parasite surface. The dominance of VAL proteins is similar to profiles reported for Ancylostoma and Haemonchus ES products. Overall, this study shows that the secretions of H. polygyrus closely parallel those of clinically important GI nematodes, confirming the value of this parasite as a model of helminth infection.