Detection and partial characterization of glycosylphosphatidylinositol-specific phospholipase activities from Fasciola hepatica and Schistosoma mansoni

Deciphering the glycogenome of schistosomes

Schistosoma mansoni and other Schistosoma sp. are multicellular parasitic helminths (worms) that infect humans and mammals worldwide. Infection by these parasites, which results in developmental maturation and sexual differentiation of the worms over a period of 5–6 weeks, induces antibodies to glycan antigens expressed in surface and secreted glycoproteins and glycolipids. There is growing interest in defining these unusual parasite-synthesized glycan antigens and using them to understand immune responses, their roles in immunomodulation, and in using glycan antigens as potential vaccine targets. A key problem in this area, however, has been the lack of information about the enzymes involved in elaborating the complex repertoire of glycans represented by the schistosome glycome. Recent availability of the nuclear genome sequences for Schistosoma sp. has created the opportunity to define the glycogenome, which represents the specific genes and cognate enzymes that generate the glycome. Here we describe the current state of information in regard to the schistosome glycogenome and glycome and highlight the important classes of glycans and glycogenes that may be important in their generation.

Immunoglobulin uptake and processing by Schistosoma mansoni

Intravascular Schistosoma mansoni worms seem to take up immunoglobulins from blood by surface Fc-receptors, but the process whereby bound immunoglobulins are processed by the parasite is poorly understood. We here present morphological data suggesting that two distinct main processes are involved: Host immunoglobulins were seen at two distinct locations in the parasite: in the frontal part of the enteric tube, the oesophagus, and as a fine granular staining at the surface and in the subtegumental region. The latter staining pattern corresponds to host immunoglobulin localization in discrete organelle-like aggregates tentatively identified as 'discoid or elongate bodies' at the ultrastructural level using immunogold staining. Immunoglobulin uptake by intravascular worms was also demonstrated in vivo after passive administration of 125I-labelled rabbit and mouse immunoglobulins. Radiolabelled immunoglobulins were taken up by the worms and shown to localize as fine strands running perpendicular to the parasite surface. Our results suggest that intravascular schistosomes take up host immunoglobulins both as part of their enteric digestion and by a surface Fc-receptor-mediated mechanism, involving transport and processing within organelles, 'elongate bodies'. Immunoglobulins taken up by intravascular schistosomes form a distinct organelle-like granules, which seem to be processed within the excretory system of the parasite.

Molecular and genetic characterisation of the host-protective oncosphere antigens of taeniid cestode parasites

Highly effective recombinant vaccines have been developed against Taenia ovis infection in sheep, Taenia saginata infection in cattle, Taenia solium infection in pigs, Echinococcus granulosus and Echinococcus multilocularis infections in a variety of intermediate host species. These vaccines have been based on the identification and expression in Escherichia coli of antigens derived from the oncosphere life cycle stage, contained within the parasites' eggs. Investigation of the molecular aspects of these proteins and the genes encoding them have revealed a number of common features, including the presence of a predicted secretory signal sequence, and one or two copies of a fibronectin type III domain, each encoded by separate exons within the associated gene. Evidence has been obtained to confirm glycosylation of some of these antigens. Ongoing investigations will shed light on the biological roles played by the proteins within the parasites and the mechanism by which they make the parasites vulnerable to vaccine-induced immune responses.

Schistosoma mansoni, S. haematobium, and S. japonicum: early events associated with penetration and migration of schistosomula through human skin

Migratory pattern of schistosomula of Schistosoma mansoni, S. haematobium, and S. japonicum through human skin were analyzed in skin organ cultures. These studies showed that the schistosomula of S. mansoni and S. haematobium has similar migratory patterns through human skin. During the first 24h after infection nearly 90% of S. mansoni and S. haematobium schistosomula were present only in the epidermis. Majority of the schistosomula were found in the dermis only after 48h and they appear to reach the dermal vessels around 72h after infection. Migratory pattern of S. japonicum on the other hand was significantly different from the other two species in that over 90% of the parasites had already reached the dermis within the first 24h and schistosomula were present in the dermal vessels within 2h after infection. Analysis of the cytokine pattern at 8h after infection by a macro gene array and RT-PCR analysis showed that out of 24 different cytokines analyzed only IL-1ra, IL-10, and TNF-alpha were increased in the human skin following infections with S. mansoni and S. haematobium, whereas, after infection with S. japonicum there was significant increases in IL-1beta, IL-1ra, IL-2, IL-6, IL-8, IL-10, IL-15, IL-18, and TNF-alpha. Immunohistochemical analysis of epidermal sheets showed focal accumulation of HLA-DR(+) cells in areas where schistosomula of S. mansoni had entered the human skin.

Mutagenesis study of the glycosylphosphatidylinositol phospholipase C of Trypanosoma brucei

The glycosylphosphatidylinositol phospholipase C (GPI-PLC) from Trypanosoma brucei is particularly effective in hydrolysing the GPI-anchors of some proteins. The enzyme is inhibited by Zn2+ and p-chloromercurylphenylsulphonic acid, both of which can act as sulphydryl reagents, suggesting that a cysteine residue may be important in catalysis. Single cysteine to serine mutants have been produced for all eight cysteines in GPI-PLC; all the mutants were fully active in vitro and were still susceptible to p-chloromercurylphenylsulphonic acid inhibition. In contrast, a single histidine 34 to glutamine mutation totally inactivated GPI-PLC. The histidine was chosen after a sequence alignment with the Bacillus cereus phosphatidylinositol phospholipase C (PI-PLC) suggested a conservation of active site residues, including histidine 34 which is central to the proposed reaction mechanism (Heinz D.W., Ryan M., Bullock T.L., Griffith O.H. EMBO J 1995;14:3855-3863). The results suggest that the GPI-PLC and bacterial PI-PLCs have conserved active sites and that the inhibition of GPI-PLC by sulphydryl reagents can occur through more than one residue.

Distribution and biophysical properties of fluorescent lipids on the surface of adult Schistosoma mansoni

The properties of 4 fluorescent lipid compounds in the surface membrane of adult male Schistosoma mansoni worms were examined by fluorescent microscopy and fluorescent recovery after photobleaching (FRAP). The data suggest that the probes N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s- indacene-3-pentanoyl) sphingosine (BODIPY FL ceramide) and PKH2 pass through the outer membrane and enter structures in or below the membrane. In contrast 5-(N-octadecanoyl)aminofluorescein (AF18) and N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s- indacene-3-pentanoyl) sphingosylphosphocholine (BODIPY FL sphingomyelin) insert into the outer monolayer. The DL values of these latter 2 compounds, 8:83 +/- 2.35 x 10(-9)cm(2)s(-1) and 2.76 +/- 0.53 x 10(-9)cm(2)s(-1), respectively, suggest that they enter different domains. Furthermore, it was observed that both BODIPY FL ceramide and BODIPY FL sphingomyelin entered particular structures in or under the surface membrane. The possible nature of these particles is discussed.

Molecular forms of tegumental and muscle acetylcholinesterases of Schistosoma

Acetylcholinesterase (AChE) is present in the muscle and on the tegument of schistosomes. Molecular forms of schistosome AChE were examined because particular AChEs are found in tissues of distinct function elsewhere. The dimeric globular form (G2) is the only form evident in adult Schistosoma haematobium: 32% of the muscle AChE is hydrophilic and 61% is membrane associated. A substantial amount of this enzyme is phosphatidylinositol (PI) anchored since it could be released by PI-specific phospholipase C from both muscle and tegumental membranes.

Praziquantel: An urgent and exciting challenge

The anthelmintic drug praziquantel has proved useful in the treatment of schistosomiasis. The precise mechanism by which praziquantel kills the parasites has yet to be elucidated. Here, John Kusel and colleagues review the current theories on praziquantel action and suggest future avenues for research, which becomes urgent in the light of some reports of drug resistance.