Schistosoma mansoni TOR is a tetraspanning orphan receptor on the parasite surface

Characterization of Schistosoma japonicum tetraspanning orphan receptor and its role in binding to complement C2 and immunoprotection against murine schistosomiasis

BACKGROUND

Schistosomiasis remains an important global public health problem, as millions of people are at risk of acquiring infection. An ideal method for sustainable control of schistosomiasis would be to develop an efficient vaccine. Schistosomes can survive in the host vascular system by immune evasion, regulating the host complement cascade. Schistosoma japonicum tetraspanning orphan receptor (SjTOR) is a complement regulator, which is a tegument membrane protein. To date there is no experimental evidence to explain the function of SjTOR.

RESULTS

We cloned the first extracellular domain of the SjTOR (SjTOR-ed1) gene and expressed the gene in Escherichia coli. The expression level of SjTOR in different developmental stages of S. japonicum was assessed by quantitative real-time RT-PCR. Western blotting showed that recombinant SjTOR-ed1 (rSjTOR-ed1) could be recognised by schistosome-infected mouse serum. Immunolocalization indicated that the protein was mainly distributed on the tegument of the parasite. Haemolytic assays and ELISA revealed that rSjTOR-ed1 could inhibit complement hemolysis and bind to complement C2. Purified rSjTOR-ed1 emulsified with ISA206 adjuvant could induce a significant reduction of worm burden from 24.51 to 26.51%, and liver egg numbers from 32.92 to 39.62% in two independent trials in mice.

CONCLUSIONS

The results of this study indicated that rSjTOR-ed1 could inhibit complement hemolysis and bind to complement C2, and it is a potential vaccine candidate that protects against S. japonicum infection.

Schistosoma mansoni tetraspanning orphan receptor (SmTOR): a new vaccine candidate against schistosomiasis

One approach to fight against schistosomiasis is to develop an efficient vaccine. Schistosoma mansoni tetraspanning orphan receptor (SmTOR) might be a vaccine candidate, as it is a tegument membrane protein expressed most highly in cercariae. In this study we characterized the recombinant first extracellular domain of SmTOR (rSmTORed1) as having the expected property to bind C2 of complement similarly to a smaller peptide of the same domain, and to produce specific and high-titre antibodies in BALB/c mice immunized using complete Freund's adjuvant/incomplete Freund's adjuvant (CFA/IFA). Immunization was protective against parasite infection, as demonstrated by a significant decrease in worm burden in immunized BALB/c mice versus the control groups over two independent trials [64 and 45% reduction for mean adult worm burden in immunized versus phosphate-bufferd saline (PBS) injected mice]. Interestingly, infection by itself did not lead to the generation of anti-rSmTORed1 antibodies, corresponding to the low frequency of specific anti-rSmTORed1 antibodies detected in the sera of patients infected with S. mansoni (2/20; 10%). These data suggest that, as opposed to the natural infection during which SmTOR induces antibodies only rarely, immunization with its smaller first extracellular domain might be more efficient.

Mefloquine interferes with glycolysis in schistosomula of Schistosoma mansoni via inhibition of enolase

The antimalarial drug mefloquine has promising antischistosomal properties killing haematophagous adult schistosomes as well as schistosomula. The mode of action and involved drug targets of mefloquine in Schistosoma mansoni schistosomula are unknown. In order to identify mefloquine-binding proteins and thus potential drug targets, mefloquine affinity chromatography with S. mansoni schistosomula crude extracts was performed. We found one specific mefloquine-binding protein that was identified by mass spectrometry as the glycolytic enzyme enolase (Q27877). Enolase activity assays were performed on schistosomula crude extracts and on the recombinant enolase Q27877 expressed in Escherichia coli. In schistosomula crude extracts enolase activity was inhibited by mefloquine and by the enolase inhibitor sodium fluoride, while activity of the recombinant enolase was not affected. In contrast to enolase from crude extracts, recombinant Q27877 did not bind to mefloquine-agarose. Using isothermal microcalorimetry, we next investigated the metabolic inhibition of mefloquine and 3 known glycolytic inhibitors in Schistosoma spp., namely sodium fluoride, 3-bromopyruvate and menadione on schistosomula in the presence or absence of glucose. We found that in the presence of glucose, schistosomula were less affected by mefloquine, sodium fluoride and 3-bromopyruvate, whereas glucose had no protective effect when schistosomula had been exposed to menadione. These results suggest a potential role of mefloquine as an inhibitor of glycolysis, at least in stages where other targets like haem degradation are not relevant.

Metabolite-biomarker investigations in the life cycle of and infection with Schistosoma

Schistosome infection is endemic in many Third World countries and affects an estimated 200 million individuals. Over the last few years, a number of investigations have focused on small molecule biomarkers of this infection. These studies were aimed at discovering key molecules relating to the life cycle of the parasite or deciphering metabolic change in the host during infection. In this review these studies are further divided into targeted approaches to find compounds and fingerprinting techniques i.e. metabonomics. A species-specific metabolite or group of biomarkers of the infection have yet to be discovered. For this reason a critical discussion contrasting with established diagnostic methods and future prospects are also provided.