Schistosoma japonicum: heterogeneity in paramyosin genes

A novel nuclear marker, Pm-int9, for phylogenetic studies of Opisthorchis felineus, Opisthorchis viverrini, and Clonorchis sinensis (Opisthorchiidae, Trematoda)

Opisthorchis felineus, O. viverrini, and Clonorchis sinensis, the trematodes of the family Opisthorchiidae, are important human parasites. Two previous studies (Kang et al. Parasitol Int 57:191-197, 2008; Katokhin et al. Dokl Biochem Biophys 421:214-217, 2008) have provided evidence using ribosomal and mitochondrial sequences that O. viverrini, O. felineus, and C. sinensis are closely related. We developed a novel nuclear marker, Pm-int9, which included the ninth intron of the paramyosin gene and flanking exon sequences. Samples of O. felineus from four localities of West Siberia, C. sinensis from the Russian Far East, and O. viverrini from Thailand were genotyped by Pm-int9. Little variation was detected in exon sequences, however, intron sequences turned out to be more variable than ribosomal internal transcribed spacers. We can conclude that Pm-int9 is valuable for interspecific variation studies. Phylogenetic analysis based on Pm-int9 revealed that O. viverrini and C. sinensis were closer to each other than either of them to O. felineus, supporting the opinion that C. sinensis should be considered the sister species of Opisthorchis spp.

Age-related and infection intensity-related shifts in antibody recognition of defined protein antigens in a schistosome-exposed population

BACKGROUND

This study compared patterns of recognition of defined Schistosoma haematobium adult worm antigens by serum antibodies from schistosome-exposed Zimbabweans aged 5-18 years.

METHODS

The population was stratified by age and infection intensity into 9 groups within which serum specimens were pooled and used to screen for protein recognition by 2-dimensional Western blotting. Recognized proteins were identified by electrospray ionizing tandem mass spectrometry.

RESULTS

A total of 71 antigens were recognized by >or=1 of the serum pools. The recognition varied distinctly with host age and infection intensity, with some isoform-specific responses. The repertoire of antigens recognized increased with age, peaking in the oldest participants whose had no or mild-to-moderate infection intensity. The intensity of antigen recognition also increased with age, peaking in the oldest participants with the heaviest infection intensity.

CONCLUSIONS

The recognition of specific schistosome antigens, both in terms of the diversity of antigens recognized and the intensity of antigen recognition, increased with duration of exposure to infection, supporting the hypothesis that the slow development of schistosome-acquired immunity is due to the slow accumulation of responsiveness to relevant parasite antigens.

Development of a vaccine against Schistosoma japonicum in China: a review

Significant progress has been made over the past 50 years in the control of schistosomiasis japonica in China. However, recent data suggest that the disease is re-emerging. By the end of 2003, Schistosoma japonicum was still endemic in 110 counties in seven provinces in the southern part of China where the long-term reduction of the disease has been replaced by an increase in the number of people infected and areas infested by the intermediate host snail, i.e. Oncomelania hupensis. Explanations are multifactorial, including the construction of the Three Gorges dam, major flooding events, recovery of the Dongting Lake and the possible impact of climate change. An efficacious vaccine against S. japonicum would represent a significant addition to the current arsenal of control tools, particularly in the framework of an integrated control approach. The vaccine could be targeted either towards the prevention of infection or towards the reduction of parasite fecundity. Although progress in this field has been relatively slow, encouraging results have been obtained in recent years using defined native and recombinantly derived S. japonicum antigens. These findings suggest that development of a safe and efficacious vaccine is feasible. This paper reviews the progress in the development of a vaccine against S. japonicum in China, and includes also data from foreign researchers who are engaged in collaborative work with Chinese scientists.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Update on paramyosin in parasitic worms

Paramyosin was first identified as a structural component of invertebrate muscle. Analysis of crude, native, adult schistosome worm preparations identified a highly immunogenic protein which was later identified as paramyosin. Early vaccination/challenge studies with native paramyosin produced encouraging levels of protective efficacy against schistosomes, which led to the question as to how a sub-tegumental (muscular) protein could provide a target for vaccine-mediated immunological attack. Immunolocalisation studies of schistosomes confirmed the presence of paramyosin within the post-acetabular glands of cercariae and on the tegumental surface of lung schistosomula. Here we present an update on the more recent research on paramyosin in parasitic worms that has focused primarily in two directions: (i) further testing of the vaccine potency of paramyosin against schistosomes and other parasitic worms; and (ii) characterisation of the protein at the molecular and biochemical levels.

Protective immunity induced by the full-length cDNA encoding paramyosin of Chinese Schistosoma japonicum

The full-length cDNA encoding paramyosin of Chinese S. japonicum (Sjc97) has been cloned and sequenced for the first time. The homology of the nucleotide sequence of paramyosin and the deduced amino acid sequence between Chinese, Philippine, Japanese strains and S. mansoni (Sm97) were 99.7, 99.8 and 96% at amino acid level, respectively; 99.4, 99.2 and 91% at nucleotide level, respectively. The immunogenicity and protective efficacy of a DNA vaccine encoding Sjc97 was evaluated in C57BL/6 mice. Mice immunized intramuscularly with pCMV-Sjc97 resulted in predominantly IgG2a and IgG2b immune responses, and immune sera were able to mediate antibody-dependent macrophage mediated cytotoxicity in vitro. Cytokine profiles in immunized C57BL/6 mice demonstrated Th1 bias, with IFN-gamma and IL-2 production and lack of IL-4 and IL-5. Immunization with pCMV-Sjc97 conferred a significant level of protection against cercariae in C57BL/6 mice. These results demonstrate that the nucleic acid encoding Sjc97 was able to induce a Th1 type immune response and confer protective efficacy in C57BL/6 mice when administrated via the intramuscular route.

Cloning of a cDNA encoding SjIrV1, a Schistosoma japonicum calcium-binding protein similar to calnexin, and expression of the recombinant protein in Escherichia coli

Membrane-associated proteins were isolated from adult Philippine strain Schistosoma japonicum by partitioning into the detergent phase of Triton X-114. A rabbit polyclonal antiserum raised against these proteins was used to screen an S. japonicum expression cDNA library. Positive clones were identified which encoded the species orthologue of SmIrV1, a Schistosoma mansoni protein which was initially identified by screening with sera from mice protectively vaccinated with irradiated cercariae [Hawn et al., J. Biol. Chem. 268 (1993) 7692-7698]. The S. japonicum molecule, which we term SjIrV1, is 83% identical to SmIrV1 at the predicted amino acid level and is a member of the calreticulin family of non-EF-hand, calcium-binding proteins. The Chinese strain S. japonicum orthologue of SjIrV1 was obtained by screening with the radiolabelled insert of the Philippine strain clone. Northern blot analysis revealed a single message of around 2.4 kb and gave no indication of alternative splicing. Southern blot analysis gave a simple pattern, indicating a single-copy gene, and showed a single restriction fragment length polymorphism between the genomes of Chinese and Philippine strains of S. japonicum. Recombinant, full-length SjIrV1 was expressed with a hexahistidine tag in Escherichia coli and the recombinant protein isolated by nickel-chelate chromatography. Recombinant SjIrV1 was shown to exhibit calcium-dependent, differential electrophoretic migration and to bind ruthenium red in the absence but not in the presence of calcium ions. The presence of conserved Ca(2+)-binding motifs predicted from the primary sequence, together with the Ca(2+)-dependent electrophoretic mobility of recombinant SjIrV1, confirmed that SjIrV1 was a functional calcium-binding protein.

The vaccine efficacy of native paramyosin (Sj-97) against Chinese Schistosoma japonicum

One of the promising anti-schistosome vaccine candidates currently under investigation is paramyosin, a 97-kDa myofibrillar protein located in the muscles and tegument of schistosome worms. Here we describe the results of two vaccination/challenge experiments undertaken in mice using native paramyosin isolated from adult worms of a Chinese strain of Schistosoma japonicum. In both sets of experiments, a relatively low but consistent and significant reduction in worm burden was evident in mice vaccinated subcutaneously with S. japonicum paramyosin and Freund's adjuvant. In contrast, intraperitoneal vaccination of mice with Chinese strain S. japonicum paramyosin without adjuvant did not result in any reduction in worm numbers when compared with a saline control group. These data contrast with the impressive protection figures reported by another group who used a similar intraperitoneal vaccination protocol with native paramyosin extracted from Philippine strain S. japonicum.

A vaccine against the Asian schistosome, Schistosoma japonicum: an update on paramyosin as a target of protective immunity

Paramyosin from parasitic worms of the genus Schistosoma has shown promise as a vaccine target and it is one of the candidates selected by WHO for the development of a vaccine against schistosomiasis. Here we discuss the literature of the past decade and report on different recombinant paramyosin constructs we are using in our laboratory to develop a vaccine against the Asian schistosoma, Schistosoma japonicum.

Oral vaccination of mice with recombinant Schistosoma japonicum proteins induces specific anti-parasite antibodies and damage to adult worms after a challenge infection

Mucosal immunisation by the oral route represents a cheap and simple method for delivering protective antigens to a host against gastrointestinal and respiratory pathogens. In the case of schistosome (bloodfluke) worms, 2 life-cycle stages may be exposed to the host's mucosa; the larval schistosomulum is exposed to the respiratory mucosa and, depending on the species, the egg may come into contact with the intestinal or urinogenital mucosa. Both IgA and some Isotypes of IgG have been implicated in protective immunity against schistosomiasis in humans and in experimental animal models. We have used a novel approach to determine whether schistosome-specific antibodies and protective immunity could be generated in mice by oral administration of bacterial lysates containing recombinant Schistosoma japonicum proteins. The mice produced specific antibodies to paramyosin and GST26, 2 important vaccine candidates for schistosomiasis, but there was no significant reduction in worm burdens in groups of mice immunised with either protein. Significantly, however, transmission electron microscopy revealed damage to the teguments of adult female and male S. japonicum worms obtained from mice vaccinated with recombinant paramyosin; there was also extensive damage to the tegument of male worms recovered from mice vaccinated with recombinant GST26. Our observations that oral vaccination with bacterial lysates containing recombinant proteins induced particular classes and subclasses of circulating antibodies with resultant damage to the surface of adult worms may have important implications for the future development of oral vaccines against a systemic infection such as schistosomiasis.