Screening trematodes for novel intervention targets: a proteomic and immunological comparison of Schistosoma haematobium, Schistosoma bovis and Echinostoma caproni

The Tao survivorship of schistosomes: implications for schistosomiasis control

Schistosomiasis, caused by blood flukes of the genus Schistosoma, is a major public health problem which contributes substantially to the economic and financial burdens of many nations in the developing world. An array of survival strategies, such as the unique structure of the tegument which acts as a major host-parasite interface, immune modulation mechanisms, gene regulation, and apoptosis and self-renewal have been adopted by schistosome parasites over the course of long-term evolution with their mammalian definitive hosts. Recent generation of complete schistosome genomes together with numerous biological, immunological, high-throughput "-omics" and gene function studies have revealed the Tao or strategies that schistosomes employ not only to promote long-term survival, but also to ensure effective life cycle transmission. New scenarios for the future control of this important neglected tropical disease will present themselves as our understanding of these Tao increases.

Clinical implications of recent findings in schistosome proteomics

Schistosomiasis is a neglected tropical disease of clinical significance that, despite years of research, still requires an effective vaccine and improved diagnostics for surveillance, control and potential elimination. Furthermore, the causes of host pathology during schistosomiasis are still not completely understood. The recent sequencing of the genomes of the three key schistosome species has enabled the discovery of many new possible vaccine and drug targets, as well as diagnostic biomarkers, using high-throughput and sensitive proteomics methods. This review focuses on the literature of the last 5 years that has reported on the use of proteomics to both better understand the biology of the schistosome parasites and the disease they cause in definitive mammalian hosts.

α2-Macroglobulin Can Crosslink Multiple Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) Molecules and May Facilitate Adhesion of Parasitized Erythrocytes

Rosetting, the adhesion of Plasmodium falciparum-infected erythrocytes to uninfected erythrocytes, involves clonal variants of the parasite protein P. falciparum erythrocyte membrane protein 1 (PfEMP1) and soluble serum factors. While rosetting is a well-known phenotypic marker of parasites associated with severe malaria, the reason for this association remains unclear, as do the molecular details of the interaction between the infected erythrocyte (IE) and the adhering erythrocytes. Here, we identify for the first time a single serum factor, the abundant serum protease inhibitor α2-macroglobulin (α2M), which is both required and sufficient for rosetting mediated by the PfEMP1 protein HB3VAR06 and some other rosette-mediating PfEMP1 proteins. We map the α2M binding site to the C terminal end of HB3VAR06, and demonstrate that α2M can bind at least four HB3VAR06 proteins, plausibly augmenting their combined avidity for host receptors. IgM has previously been identified as a rosette-facilitating soluble factor that acts in a similar way, but it cannot induce rosetting on its own. This is in contrast to α2M and probably due to the more limited cross-linking potential of IgM. Nevertheless, we show that IgM works synergistically with α2M and markedly lowers the concentration of α2M required for rosetting. Finally, HB3VAR06+ IEs share the capacity to bind α2M with subsets of genotypically distinct P. falciparum isolates forming rosettes in vitro and of patient parasite isolates ex vivo. Together, our results are evidence that P. falciparum parasites exploit α2M (and IgM) to expand the repertoire of host receptors available for PfEMP1-mediated IE adhesion, such as the erythrocyte carbohydrate moieties that lead to formation of rosettes. It is likely that this mechanism also affects IE adhesion to receptors on vascular endothelium. The study opens opportunities for broad-ranging immunological interventions targeting the α2M--(and IgM-) binding domains of PfEMP1, which would be independent of the host receptor specificity of clinically important PfEMP1 antigens.

The helminth parasite proteome at the host-parasite interface - Informing diagnosis and control

Helminth parasites are a significant health burden for humans in the developing world and also cause substantial economic losses in livestock production across the world. The combined lack of vaccines for the major human and veterinary helminth parasites in addition to the development of drug resistance to anthelmintics in sheep and cattle mean that controlling helminth infection and pathology remains a challenge. However, recent high throughput technological advances mean that screening for potential drug and vaccine candidates is now easier than in previous decades. A better understanding of the host-parasite interactions occurring during infection and pathology and identifying pathways that can be therapeutically targeted for more effective and 'evolution proof' interventions is now required. This review highlights some of the advances that have been made in understanding the host-parasite interface in helminth infections using studies of the temporal expression of parasite proteins, i.e. the parasite proteome, and discuss areas for potential future research and translation.

Of monkeys and men: immunomic profiling of sera from humans and non-human primates resistant to schistosomiasis reveals novel potential vaccine candidates

Schistosoma haematobium affects more than 100 million people throughout Africa and is the causative agent of urogenital schistosomiasis. The parasite is strongly associated with urothelial cancer in infected individuals and as such is designated a group I carcinogen by the International Agency for Research on Cancer. Using a protein microarray containing schistosome proteins, we sought to identify antigens that were the targets of protective IgG1 immune responses in S. haematobium-exposed individuals that acquire drug-induced resistance (DIR) to schistosomiasis after praziquantel treatment. Numerous antigens with known vaccine potential were identified, including calpain (Smp80), tetraspanins, glutathione-S-transferases, and glucose transporters (SGTP1), as well as previously uncharacterized proteins. Reactive IgG1 responses were not elevated in exposed individuals who did not acquire DIR. To complement our human subjects study, we screened for antigen targets of rhesus macaques rendered resistant to S. japonicum by experimental infection followed by self-cure, and discovered a number of new and known vaccine targets, including major targets recognized by our human subjects. This study has further validated the immunomics-based approach to schistosomiasis vaccine antigen discovery and identified numerous novel potential vaccine antigens.

Immunoproteomic analysis of Schistosoma japonicum schistosomulum proteins recognized by immunoglobulin G in the sera of susceptible and non-susceptible hosts

The aim of this study was to search for immunogenic schistosomula proteins in the hope of identifying novel intervention targets. Schistosomula proteins were analyzed by immunoproteomic which the probes were sera derived from BALB/c mice (susceptible hosts) and Microtus fortis (resistant hosts). A total of 116 immunoreactive proteins recognized by 10 days post-infected BALB/c mice, M. fortis sera, and uninfected M. fortis sera were selected for further analysis. Finally, 95 protein spots were identified by mass spectrometry (MS) analysis. Bioinformatics analysis showed that the differentially identified immunogenic proteins participated mainly in cytoskeleton organization, cell motility, energy metabolism, responses to stimuli, and protein folding. Many of these proteins were the tegument or excretory-secretory products of schistosomes reported in previous studies. Among of them, Schistosoma japonicum DnaJ (Hsp40) homologue (SjDnaJ) was successfully expressed and the purified recombinant product was evaluated by immunoprotective experiment. After immunization of BALB/c mice with recombinant SjDnaJ, it could induce 34.5% and 48.9% reductions in the numbers of worms and eggs in the liver. These results contribute to a better understanding of the molecular mechanisms underlying the host-parasite relationship and provide a major dataset to facilitate the further development of new vaccine candidates and/or diagnostic markers for schistosomiasis.

BIOLOGICAL SIGNIFICANCE

Schistosomiasis is caused by parasitic blood-dwelling flukes in tropical and subtropical areas, and it is one of the world's most prevalent tropical diseases. The lack of effective vaccine and reliable diagnostic methods make this disease difficult to control. In China, S. japonicum can infect more than 40 different susceptible mammals for this parasite. However, M. fortis is the only known mammal where the schistosome cannot develop and it exhibits no significant pathological effects. Many studies' results showed that native antibodies against S. japonicum are present in M. fortis that may have important anti-schistosomiasis roles during the infection process. The aim of this study was to search for immunogenic schistosomula proteins in the hope of identifying novel intervention targets. We present a comparative immunoproteomics analysis of the proteins recognized by susceptible and resistant host antibodies before and 10-days after infections. The results of this analysis will be helpful for identifying the key molecules required for the survival and development of schistosomes. At the same time, the study contributes to a better understanding of the molecular mechanisms underlying the host-parasite relationship associated with schistosomes and they also provide a major dataset to facilitate the further development of new diagnostic assays and/or vaccine candidates for schistosomiasis.

Screening diagnostic candidates for schistosomiasis from tegument proteins of adult Schistosoma japonicum using an immunoproteomic approach

BACKGROUND

Schistosomiasis is one of the world's most prevalent zoonotic diseases and a serious worldwide public health problem. Since the tegument (TG) of Schistosoma japonicum is in direct contact with the host and induces a host immune response against infection, the identification of immune response target molecules in the schistosome TG is crucial for screening diagnostic antigens for this disease.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, an immunoproteomics approach used TG proteins as screening antigens to identify potential diagnostic molecules of S. japonicum. Ten spots corresponding to six proteins were identified that immunoreacted with sera from S. japonicum-infected rabbits but not sera from uninfected rabbits and their specific IgG antibody levels declined quickly after praziquantel treatment. Recombinant phosphoglycerate mutase (PGM) and UV excision repair protein RAD23 homolog B (RAD23) proteins were expressed and their diagnostic potential for schistosomiasis was evaluated and compared with schistosome soluble egg antigen (SEA) using ELISA. The results showed high sensitivity and specificity and low crossreactivity when rSjPGM-ELISA and rSjRAD23-ELISA were used to detect water buffalo schistosomiasis. Moreover, antibodies to rSjPGM and rSjRAD23 might be short-lived since they declined quickly after chemotherapy.

CONCLUSION/SIGNIFICANCE

Therefore, the two schistosome TG proteins SjPGM and SjRAD23 were identified as potential diagnostic markers for the disease. The two recombinant proteins might have the potential to evaluate the effectiveness of drug treatments and for distinguishing between current and past infection.

Serological screening of the Schistosoma mansoni adult worm proteome

BACKGROUND

New interventions tools are a priority for schistosomiasis control and elimination, as the disease is still highly prevalent. The identification of proteins associated with active infection and protective immune response may constitute the basis for the development of a successful vaccine and could also indicate new diagnostic candidates. In this context, post-genomic technologies have been progressing, resulting in a more rational discovery of new biomarkers of resistance and antigens for diagnosis.

METHODOLOGY/PRINCIPAL FINDINGS

Two-dimensional electrophoresed Schistosoma mansoni adult worm protein extracts were probed with pooled sera of infected and non-infected (naturally resistant) individuals from a S. mansoni endemic area. A total of 47 different immunoreactive proteins were identified by mass spectrometry. Although the different pooled sera shared most of the immunoreactive protein spots, nine protein spots reacted exclusively with the serum pool of infected individuals, which correspond to annexin, major egg antigen, troponin T, filamin, disulphide-isomerase ER-60 precursor, actin and reticulocalbin. One protein spot, corresponding to eukaryotic translation elongation factor, reacted exclusively with the pooled sera of non-infected individuals living in the endemic area. Western blotting of two selected recombinant proteins, major egg antigen and hemoglobinase, showed a similar recognition pattern of that of the native protein.

CONCLUDING/SIGNIFICANCE

Using a serological proteome analysis, a group of antigens related to the different infection status of the endemic area residents was identified and may be related to susceptibility or resistance to infection.

Progress in paediatric parasitology: a preface to a topic focusing on ever younger subjects

Without realizing it perhaps, the research activities of many parasitologists are often focused upon the study of parasites most commonly found in children. Though there is little recognition of paediatric parasitology as a separate topic within medical parasitology, with the global interest in promotion of maternal and child health, alleviation of diseases associated with poverty and requirements of 'child-sized' medicines, a more formal consideration is now timely. Recent research, for example, has highlighted that defining precisely the 'first-age' at which parasites interfere with a child's health, or normal developmental processes, is being revised. Attention is now drawn towards ever younger subjects, for parasites have the capacity to also influence the health of the foetus within the in utero environment, altering immune-development. These subtle, yet evolutionary profound interactions perhaps manifest themselves as to why some children are more prone to infection(s), develop overt disease and sadly die while others do not. Here, we address the growing importance of paediatric parasitology and its applications within disease control strategies as highlighted in the 2010 Autumn Symposium of the British Society of Parasitology.