Adult schistosome cDNA libraries as a source of antigens for the study of experimental and human schistosomiasis

Vaccination of patas monkeys experimentally infected with Schistosoma haematobium using a recombinant glutathione S-transferase cloned from S. mansoni

The capacity of a recombinant glutathione S-transferase from Schistosoma mansoni (rSm28GST) to vaccinate primates (Erythrocebus patas) against a heterologous infection with Schistosoma haematobium has been tested. Two injections of the purified molecule with Muramyl-Di-Peptide (MDP) as adjuvant resulted in a high level antibody response in the five immunized animals and in a significant reduction in worm fecundity compared to the controls which received adjuvant alone. Mean levels of daily egg excretion in urine an faeces were reduced by respectively 55% and 74% although perfusion revealed that worm burdens were similar in both groups. The protective effect was long lasting since it was maintained up to the end of the experiment, 42 weeks after infection. Hatching rates and the numbers of intra-uterine eggs were also significantly affected by the vaccination. Tissue eggs were also drastically diminished in the urogenital system (-80%) but the reduction was not statistically significant. One animal was not protected by the immunization. There was a good correlation between parasitological data and the intensity of bladder lesions assessed by microscopic examination. Polypoid formations together with an intense exudation of the lamina propria were frequently seen in the controls but rarely in the vaccinated group where formation of scar tissue was predominant. These results underline the vaccine potential of the recombinant Sm28GST as a possible valuable prophylactic tool for the control of egg-induced pathology and transmission of African schistosomes.

Cloning of a 21.7-kDa vaccine-dominant antigen gene of Schistosoma mansoni reveals an EF hand-like motif

Several cDNA clones encoding a 21.7-kDa antigen (Sm21.7) were detected from a Schistosoma mansoni sporocyst cDNA expression library using irradiated cercaria-vaccinated rabbit serum. The antigen was designated 'vaccine dominant' because parasite-derived Sm21.7 was recognised preferentially by mouse vaccine sera compared with mouse infection sera. The cDNA and corresponding gDNA sequences showed 64% identity at the nucleotide level and 47% identity at the amino acid level with the sequence of a previously described S. mansoni tegumental antigen, sma22.6. Whereas sma22.6 mRNA occurs almost exclusively in the adult worm, Sm21.7 mRNA was equally abundant in the sporocyst, schistosomular and adult stages. Both Sm21.7 and sma22.6 sequences reveal a motif strongly homologous to the EF hand calcium binding domain but lacking the invariant glycine in the calcium binding loop. The disruptive nature of the glutamine which in Sm21.7 replaces the glycine explains why the motif is non-functional, as shown by the inability of Sm21.7 to bind calcium.

Molecular cloning and characterisation of the 22-kilodalton adult Schistosoma mansoni antigen recognised by antibodies from mice protectively vaccinated with isolated tegumental surface membranes

A cDNA clone from an adult Schistosoma mansoni lambda gt11 expression library (A12) encoding an antigenic polypeptide of 22 kDa is described. A12 is 797 bp long and has one open reading frame encoding a protein of 190 amino acids which does not contain a signal sequence or membrane anchor motif and has no homologies with any sequences on the currently available data bases. Its product (sm22.6) is recognised by antibodies from mice protectively vaccinated with purified adult S. mansoni tegumental membranes and by serum from S. mansoni-infected Brazilians. It is present in all post-snail life cycle stages except the egg, is not sex-specific, and is found in 9 species of Schistosoma, but not in a range of other helminths. Data are presented which suggest that sm22.6 is a soluble, peripheral membrane protein.

A cDNA clone encoding part of the major 25,000-dalton surface membrane antigen of adult Schistosoma mansoni

Immunoscreening of an adult Schistosoma mansoni cDNA expression library, using antibodies raised against purified adult worm tegumental surface membranes, identified a recombinant clone containing a 141-bp insert. Antibodies raised against the recombinant antigen bound specifically to the tegument of adult worms and immunoprecipitated the major 25,000-dalton surface membrane antigen as well as a 22,000-dalton nascent polypeptide generated by cell-free translation of adult S. mansoni mRNA. The mature 25,000-dalton antigen was found to be precipitated by antibodies from infected mice, rats and humans.

Comparison of the in vitro translation capacity of Taenia crassiceps metacestode mRNA prepared by the phenol and cesium chloride method

Total RNA of T. crassiceps metacestodes harvested from male and female NMRI mice was prepared by both the phenol extraction technique and cesium chloride (CsCl) gradient centrifugation. mRNA was selected by oligo (dT)-cellulose affinity chromatography and used as the template for the in vitro translation of parasite polypeptides in a cell-free rabbit reticulocyte lysate. The template activity of the mRNA obtained after CsCl preparation was clearly higher, as shown by the amount of 35S-methionine incorporated into the translation products and by fluorographed SDS-PAGE of the synthesized labelled polypeptides. SDS-PAGE fluorographs of antigens encoded by the mRNA prepared by CsCl centrifugation and selected by immunoprecipitation using purified IgG antibodies of T. crassiceps-infected mice (day 80 postinfection) exhibited seven labelled polypeptides of about 65, 46, 45, 42, 34, 29 kDa and a predominant 20-kDa antigen. The latter polypeptide was the only one recognized by the antibodies amongst the in vitro translation products directed by mRNA prepared by the phenol method.

Surface and species-specific antigens of Schistosoma haematobium

Of the surface antigens identified by radio-iodination, two-dimensional gel analyses showed no similarities between those of Schistosoma haematobium and Schistosoma mansoni, thus providing a basis for the species specificity of these antigens described previously (Simpson, Knight, Hagan, Hodgson, Wilkins & Smithers (1985) Parasitology 90, 499-508). The surface antigens of S. haematobium were glycosylated and comprised an acidic polypeptide of Mr 17,000 as well as a complex set of polypeptides of approximate pI 6-7, which resolved in the Mr range 20,000-30,000. At least one of the lower Mr forms of this complex is also present in the adult worm. Limited cross-reaction was observed with S. mansoni infection sera and this may be due to a shared carbohydrate epitope. In contrast, extensive cross-reaction was observed using sera from mice immunized with S. bovis. This pattern parallels the species-specificity of vaccine-induced immunity. Extensive cross-reaction was also observed within cell-free translation products of m-RNA from adult worms of S. haematobium and S. mansoni by use of heterologous human infection sera. The few antigens which were species-specific may represent surface antigens.

Cloning of a Schistosoma japonicum gene encoding a major immunogen recognized by hyperinfected rabbits

A library of randomly sheared Schistosoma japonicum genomic DNA fragments was constructed in the bacteriophage expression vector lambda gt11. A portion of the library was screened with sera collected from rabbits 8 weeks after they were infected with 1000 cercariae. Four clones whose recombinant gene products react with the rabbit sera were purified to homogeneity. Clone SjIR-12A was chosen for detailed study because of its very intense reaction with the rabbit sera. SjIR-12A was found to encode part of a 70 kDa protein (Sj70) that is present in both soluble egg antigen (SEA) and soluble worm antigen preparations (SWAP). Western blot analysis suggests that Sj70 is the only SWAP component that is strongly immunoreactive with the rabbit sera. Rabbit antibodies that react with the SjIR-12A fusion protein were immunoaffinity purified and used to localize immunoreactive product to the nervous tissue of male and female adult worms, the dorsal and lateral tegument of male adult worms, and in eggs to the miracidial tegument and the area between the eggshell and miracidium. Southern hybridization analysis suggests there are approximately four copies of the Sj70 gene per haploid genome.

Cloning of a cDNA encoding a surface antigen of Schistosoma mansoni schistosomula recognized by sera of vaccinated mice

Spleen cells of mice vaccinated with radiation-attenuated Schistosoma mansoni cercariae were used to produce monoclonal antibodies directed against newly transformed schistosomular surface antigens. One of these monoclonal antibodies recognized a polypeptide of 18 kDa. This glycoprotein was purified by monoclonal antibody immunoaffinity chromatography and a polyclonal antiserum was prepared against it. Immunofluorescence assays showed that the polyclonal antiserum bound to the surface of newly transformed schistosomula and lung-stage organisms but not to the surface of liver-stage and adult worms. Using this polyclonal antiserum we isolated recombinant clones from an adult worm cDNA expression library constructed in lambda gt11. Clone 654.2 contained an insert of 0.52 kilobase and hybridized to a 1.2-kilobase mRNA species from adult worms. Most importantly, clone 654.2 produced a fusion protein of 125 kDa that was reactive with sera of vaccinated mice that are capable of transferring resistance. This result encourages future vaccination trials with the fusion protein.

The present status of serodiagnosis and seroepidemiology of schistosomiasis

The literature of the past 4-5 yr on serodiagnosis and seroepidemiology of schistosomiasis is reviewed. A variety of assays with different antigens are being used for serodiagnosis. Several purified antigens appear to be sensitive and specific, but have little if any capability of indicating duration of infection, parasite burden, or effect of chemotherapy. The results of long-term posttherapy field studies indicate that serology has a role in monitoring control programs. Standardized serologic assays and the need for International Standard Reference Sera are emphasized. A standardized enzyme-linked immunosorbent assay based on the Falcon Assay Screening Test system (FAST-ELISA), and involving a standard reference serum pool, is suitable for both serodiagnosis and field studies. Measurement of circulating antigens as a parameter of active infection is considered to have increased potential, compared with antibody measurement, in management of clinical disease and in control programs. Recombinant DNA technology may be useful for producing standard antigens for use in assays measuring antibody or circulating antigen. Time-resolved immunofluorescence involving europium-labeled conjugates may provide the increased assay sensitivity needed for measurement of circulating antigen.

Isolation of lambda amp3 genomic recombinants coding for antigens of Eimeria tenella

Eimeria are the causative agents of coccidosis, a disease which is of world wide economic importance in the poultry industry. Immunity resulting from infection is species-specific and both antibody and cell-mediated responses have been implicated. As an initial step in the development of a genetically-engineered vaccine against coccidiosis, libraries of EcoRI-digested genomic DNA from E. tenella have been constructed in Escherichia coli using the expression vector lambda amp3. Screening of the libraries with serum from chickens immunized by infection has identified at least 24 different recombinant phage which produce eimeria antigens fused to beta-galactosidase. A significant proportion of the Eimeria DNA inserts cross-hybridise with each other and contain sequences which are highly represented in the genome. The identification of these clones will enable the isolation of intact genes from E. tenella DNA and facilitate detailed analysis of the antigens and immune responses.

The cloning of schistosome genes encoding antigenic and maturation-linked polypeptides

Schistosomiasis is a chronic debilitating disease which accounts for considerable human mortality and morbidity and is second only to malaria in its prevalence and severity. Despite several years of concentrated effort to combat the disease with molluscicides and chemotherapy, schistosomiasis is still spreading, and it is thought that 500 million people are currently exposed to infection (larotski & Davis, 1981).