Vaccination against Schistosoma mansoni with purified surface antigens

Macaque models of human infectious disease

Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents—bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease.

Protective immunity and vaccines to schistosomiasis

Human schistosomiasis is a major health problem in endemic areas and it is estimated that world-wide more than 200 million people are infected. Active infection, exposure to attenuated parasites, or appropriate immunization with parasite extracts or purified antigens can lead to partial protection against challenge infections. Studies of the humoral and cellular mechanisms responsible for these forms of resistance, and the definition, purification or production of recombinant moieties responsible for the induction of immunity are currently the focus of considerable research efforts.

Protective immunity induced in mice by F8.1 and F8.2 antigens purified from Schistosoma mansoni eggs

Schistosoma mansoni soluble egg antigens (SEA) were fractionated by isoelectric focusing, resulting in 20 components, characterized by pH, absorbance and protein concentration. The higher absorbance fractions were submitted to electrophoresis, and fraction 8 (F8) presented a specific pattern of bands on its isoelectric point. Protein 3 was observed only on F8, and so, it was utilized to rabbit immunization, in order to evaluate its capacity of inducing protective immunity. IgG antibodies from rabbit anti-F8 serum were coupled to Sepharose, and used to obtain the specific antigen by affinity chromatography. This antigen, submitted to electrophoresis, presented two proteic bands (F8.1 and F8.2), which were transferred to nitrocellulose membrane (PVDF) and sequenciated. The homology of F8.2 to known proteins was determined using the Basic Local Alignment Search Tool program (BLASTp). Significant homologies were obtained for the rabbit cytosolic Ca2+ uptake inhibitor, and for the bird a1-proteinase inhibitor. Immunization of mice with F8.1 and F8.2, in the presence of Corynebacterium parvum and Al(OH)3 as adjuvant, induced a significant protection degree against challenge infection, as observed by the decrease on worm burden recovered from portal system.

Induction of protective immunity against Schistosoma mansoni infection by antigens purified from PIII, a fraction of adult worm, associated to the downregulation of granuloma formation

This study was performed in order to define Schistosoma mansoni antigens able to function as modulator agents in BALB/c mice granulomatous hypersensitivity to parasite egg. The antigens P-24, P-35 and P-97 were purified by affinity chromatography from a fraction of S. mansoni adult worm antigenic preparation, denominated PIII, involved in the inhibition of granulomatous response to eggs. Immunization of mice with these antigens, in the presence of Corynebacterium parvum and Al(OH)3 as adjuvant, induced a significant protection degree against challenge infection, as observed by the decrease on worm burden recovered from portal system. In vitro blastogenesis assays revealed that purified antigens were able to induce significant proliferation of spleen cells from S. mansoni-infected mice. This protection was correlated to significant decrease in granuloma size induced by PIII. From these results, we concluded that PIII preparation contains antigens capable of mediating protective anti-parasite immunity and down-regulating granulomatous hypersensitivity to S. mansoni eggs.

Characterization of Schistosoma mansoni 44.7/56.8 kDa egg antigens recognized by human monoclonal antibodies which induce protection against experimental infection and proliferation of peripheral blood mononuclear cells from schistosomiasis patients

We described here the characterization of Schistosoma mansoni egg antigens recognized by human monoclonal antibodies B10 (HmAb-B10) and D5 (HmAb-D5). SDS-PAGE and Western blot analysis revealed that these monoclonals recognized two antigens of M W 44.7/56.8 kDa, with pI of 7.0 and 7.8, respectively. The passive transfer of B10 and D5 induced a significant protection of 48% and 54% in Balbic mice. Results of in vitro cytotoxicity assay showed that both monoclonals were able to kill schistosomula in the presence of rabbit complement. These monoclonals mediated 48% and 74% of schistosomula cytotoxicity, respectively. Egg antigens were purified by affinity chromatography using monoclonal antibodies B10 and D5. Treatment of purified antigens with periodate, galactose oxidase and trifluoromethane sulphonic acid did not prevent binding by B10 and D5 in ELISA assay. However, the treatment with protease K and 2-mercaptoethanol affects the antibodies binding, showing that the HmAbs B10 and D5 recognize polypeptide epitopes. Vaccination of mice with these antigens in Freund's adjuvant induced 43% reduction in worms burden after challenge with S. mansoni cercariae. In vitro blastogenesis assays with peripheral blood mononuclear cells from patients infected with S. mansoni revealed that purified antigens were able to induce significant cell proliferation.

Schistosoma mansoni: identification of a 46KDa antigen of the schistosomular surface by monoclonal antibody

An IgG2a subclass monoclonal antibody, C6G9, was obtained by immunization of BALB/c mice with Schistosoma mansoni egg antigens. With this monoclonal antibody, it was possible to identify a schistosomular antigen with a molecular weight of 46 kilodaltons (KDa), and its expression being evaluated by means of indirect immunofluorescence. The antigen persisted in the integument of the developing schistosomulum, for at least 96 hours post-transformation. The monoclonal antibody also reacted with the cercaria surface, but not with that of adult worm. The C6G9 was also able to mediate significant levels of cytotoxicity in the presence of complement for newly transformed schistosomula.

IL-1, TNF-alpha and IL-2 production by peritoneal and spleen cells from Schistosoma mansoni infected mice and its potentiation by preimmunization with schistosomal antigens and immunostimulants

In the present study we tested the effect of immunization with schistosome derived antigens such as frozen-thawed schistosomula in combination with either BCG, liposomes or liposomal muramyl tripeptide-phosphatidyl ethanolamine (MTP-PE), on the resistance of mice to infection, and on the function of their macrophages and lymphocytes. Immunization with either F-T schistosomula + BCG or F-T schistosomula + MTP-PE and subsequent infection, resulted in a 2-3-fold increase in adherent peritoneal macrophage-mediated schistosomulicidal activity (SCA). Peritoneal and spleen macrophages from immunostimulant treated and/or immunized animals showed a significant increase in LPS triggered TNF-alpha production, as compared to non-treated controls. The highest increase in TNF-alpha production was achieved after immunization with either F-T schistosomula + BCG or F-T schistosomula + MTP-PE. LPS triggered IL-1 production was elevated in spleen and peritoneal macrophages from F-T schistosomula + BCG treated mice, and also in spleen macrophages treated with F-T schistosomula + MTP-PE. Only immunization with F-T schistosomula + BCG increased ConA-induced spleen lymphocyte proliferation and IL-2 production. Immunization of mice with F-T schistosomula + BCG also induced protection against parasite infection, while F-T schistosomula + MTP-PE failed to do so. Potentiation of antischistosomal resistance seems to require both macrophage and lymphocyte activation which was achieved only when BCG served as an immunostimulant.

Purification of two murine monoclonal antibodies of the IgM class by hydroxylapatite chromatography and gel filtration

A two-step method using hydroxylapatite chromatography and gel filtration is described for the purification of two murine monoclonal antibodies of the IgM class. Ascites fluid from each hybridoma was diluted in sodium phosphate buffer (0.01 M, pH 6.8), loaded onto a hydroxylapatite column and eluted with a stepwise sodium phosphate gradient. The immunoreactive protein peaks were concentrated and subjected to gel filtration using either Sephadex G-200 or Sephacryl S-200HR. The biological activity of the end-products was confirmed by complement lysis assay and by indirect immunofluorescence and flow cytometry. The purity of the end-products as assessed by SDS polyacrylamide gel electrophoresis and densitometry was at least 90%. The methods described produced immunoreactive material with a high level of purity. The procedure for each antibody was reproducible and provides a reliable method for purification of monoclonal antibodies of the IgM class.

Human hybridoma generation by hypo-osmolar electrofusion: characterization of human monoclonal antibodies to Schistosoma mansoni parasite antigens

Human monoclonal antibodies which bind Schistosoma mansoni worm and egg antigens were identified and characterized from hybridomas generated using the hypo-osmolar electrofusion technique of somatic cell fusion. Splenocytes from S. mansoni infected individuals were mitogen-activated in vitro and subsequently fused by electrofusion. The greatest number of HAT resistant hybridomas per helical fusion chamber was obtained with unfrozen splenocytes cultured for 4-6 days after introduction of mitogen. Hybridomas secreting IgG antibodies recognizing parasite antigens were identified by ELISA. Twenty-one cloned cell lines secreting IgG antibody were maintained for at least 6 months. Characterization of antigen reactivity by Western blot analysis of nien cloned cell lines revealed antibodies which bound stage specific parasitic antigens. The data show that the technique of hypo-osmolar electrofusion produces stable, antibody producing hybridomas. The human monoclonal antibodies screened represent candidate molecules useful in the investigations of the human pathogen S. mansoni.

On the interaction between macrophages and developmental stages of Schistosoma mansoni: effect of muramyl tripeptide phosphatidyl ethanolamine (MTP-PE) treatment on mice survival and the generation of schistosomulicidal macrophages

Schistosomiasis is a chronic disease afflicting hundreds of millions of people throughout the world against which there is as yet no effective vaccine. In the present study we tested the effect of the immunomodulator muramyl tripeptide phosphatidyl ethanolamine (MTP-PE) on the survival of Schistosoma mansoni-infected mice and on the induction in them of schistosomulicidal macrophages. Mice exposed to 80 cercariae each and then treated with MTP-PE showed prolonged survival following either single or repeat infection. The treatment with MTP-PE, when initiated 70 days post the schistosome infection, diminished significantly the mortality of infected mice over an observed period of 110 days. In terms of treatment efficacy there was no evident difference between the intravenous and intraperitoneal mode of administration of the drug. MTP-PE treatment significantly reduced granuloma size and markedly diminished liver damaged as judged by the lower levels of alkaline phosphatase in the serum. Such treatment exerted no significant effect on the spleen or liver weight in infected mice nor on the worm burden resulting from either a single or double infection. In infected and non-treated mice, schistosomulicidal macrophages appeared after 8-10 weeks of infection. In infected mice treated with MTP-PE there was an accelerated appearance of such macrophages and these exhibited a greater cidal effect on the schistosomula. These immunostimulatory and life-prolonging effects of MTP-PE on S. mansoni-infected mice might indicate an effect of this reagent on cells involved in the granulomatous process.

Immunization of mice and baboons with the recombinant Sm28GST affects both worm viability and fecundity after experimental infection with Schistosoma mansoni

A member of the glutathione S-transferase family, Sm28GST has previously demonstrated a good ability to protect rodents against experimental infection with Schistosoma mansoni. In order to evaluate its efficacy in a model closer to man, two different protocols of immunization with recombinant Sm28GST were tested on baboons in a large-scale trial. Three injections in the presence of aluminium hydroxide as adjuvant resulted in a significant 38% reduction in the adult worm burden together with a trend for a lower percentage of inflammatory tissue in the liver. Individual levels of protection, ranging from 0 to 80%, underlined the heterogeneity of the immune response to this purified molecule in outbred primates. On the other hand, two injections of Sm28GST in the presence of aluminium hydroxide and Bordetella pertussis reduced female schistosome fecundity by 33%, with a more pronounced effect (66%) on faecal egg output; there was also a trend, in this protocol, for decrease of the mean granuloma surface in the liver. Individual anti-Sm28GST IgG antibodies were apparently unrelated to levels of immunity, but there was partial evidence that cytophilic IgE might play a role in the immune mechanisms affecting worm viability, but not fecundity. In the mouse model, Sm28GST vaccination resulted in a lower hatching ability of tissue eggs recovered from immunized mice whereas passive transfer of specific anti-Sm28GST T-lymphocytes, one day before infection, significantly reduced the number of eggs in the liver of mice. We propose that different protocols of immunization with a recombinant molecule can impede Schistosoma mansoni worm viability and fecundity, but can also affect miracidium physiology, with important consequences for disease transmission and granuloma-derived pathology.

Protective immunity to Schistosoma mansoni in mice is dependent on antibody and complement but not on radiosensitive leukocytes

The role of complement in the control of the Schistosoma mansoni infection in mice was investigated in vivo. The number of schistosomula recovered from the lung 5 days post-infection was used as a parasitological criterion of immunity. A significant difference in worm burden was observed between normal and immune mice. In contrast, when cobra venom factor (CVF) was injected into normal or immune mice 3 h before challenge, a significant increase in worm burden was noticed compared to untreated mice. We also investigated the protective mechanisms in mice that had been exposed to 650 rads of 60Co gamma radiation before challenge infection. Our results show that gamma-irradiated immune mice, depleted of more than 90% of their circulating or tissue leukocytes, are still able to destroy most of the parasites of a challenge infection with cercariae, suggesting that the radiosensitive leukocytes are not essential in the effector mechanisms of this protective immunity to S. mansoni. These results provide evidence of a role for the complement system, in association with radioresistant effector cells, in protective immunity occurring in the first hours after infection with S. mansoni.

Schistosome vaccines

Schistosomiasis control currently relies primarily on chemotherapy which is both expensive and temporary. There is an urgent need for an effective vaccine. Studies in animal models and man have demonstrated the existence of protective immunity. Antibody-dependent cell-mediated cytotoxicity mechanisms involving eosinophils and macrophages have been implemented in destruction of the parasites. Antigens expressed on the surface of the schistosomulum are among the targets of protective immune responses. Vaccines comprising recombinant antigens are now being tested in vivo for their capacity to evoke protective responses. Live oral vaccines based on attenuated Salmonella expressing schistosomular surface antigens are being developed.

Production and characterization of human monoclonal antibodies against Schistosoma mansoni

We have produced a panel of human monoclonal antibodies (MoAb) from patients infected with Schistosoma mansoni in order to analyse more carefully the human immune response to this helminth infection. This study describes the production, characterization and analysis of these MoAbs. Briefly, peripheral blood mononuclear cells from chronically infected patients were (1) isolated and stimulated with parasite antigens in vitro, (2) positively selected for B-cells on anti-Ig columns, and (3) then transformed with Epstein-Barr virus (EBV). Once EBV cell lines were established, they were selected for anti-S. mansoni antibodies using an ELISA, cloned, retested and then fused with the mouse-human heteromyeloma SHM-D33. In this study, we describe five MoAbs which have different antigenic specificities for life-cycle stages based on ELISA to soluble crude antigen preparations, membrane immunofluorescence on whole intact organisms, and immunofluorescent staining of cryostat frozen sections. The importance of these reagents with regard to the human immune response to S. mansoni is currently being evaluated.

Induction of resistance to Schistosoma mansoni infection in mice by purified parasite paramyosin

Freeze-thaw (FT)-disrupted schistosomula or their membrane extract induced significant resistance in mice to Schistosoma mansoni infection (34 and 25%, respectively) without the use of adjuvant. Antigens identified in schistosome extracts by sera from immunized animals were then evaluated for protective potential. Immunization with schistosomal antigens of 97 and 68-70 kD resulted in significant protection that was equivalent to that obtained by FT schistosomula. Since the 97-kD antigen was suggested to be parasite paramyosin, we used a biochemical technique to purify this muscle protein. Purified schistosome paramyosin ran as a single band on 10% SDS-PAGE and was recognized both by sera from mice immunized with FT schistosomula and a polyclonal antiserum raised against the 97-kD parasite protein. Preincubation of schistosome paramyosin with sera from mice immunized with FT schistosomula resulted in the removal of reactivity with the 97-kD protein in crude worm extracts. Paramyosin was identified by Western blotting to be in the tegument of schistosomula. The purified schistosome paramyosin resulted in significant protection in three separate experiments (24, 46, and 53%) without the use of adjuvant. Addition of BCG to paramyosin resulted in enhanced protection.

Antiidiotypic antibody vaccine in murine Schistosomiasis mansoni comprising the internal image of antigen

This study presents the characterization of an experimental immunotherapeutic approach for schistosomiasis utilizing antiidiotypic antibodies. Antiidiotype (31-3B6) was generated in rabbits using a protective murine monoclonal antibody 31-3B6 which recognizes a 68,000-D molecular mass glycoprotein present in extracts of Schistosomiasis mansoni adult worm homogenetics. Immunization of mice with antiidiotype (31-3B6) before S. mansoni cercariae infection resulted in protection levels ranging from 16 to 41% depending on the route of administration of antiidiotypic antibody and the use of adjuvant. Levels of protection as high as 25% could be obtained with a single injection of antiidiotype (31-3B6) without the use of adjuvant. Animals noted to be resistant to infection with S. mansoni cercariae were also noted to exhibit a humoral immune response that bound components of S. mansoni adult worm homogenetics. This induced antiantigen immune response was shown to bind to the surface of S. mansoni schistosoma by indirect immunofluorescence. Further characterization of the induced antiantigen response showed that a portion (3-32%) of the induced humoral immune response portrayed the binding specificities of the murine monoclonal antibody 31-3B6. The data indicate that antiidiotype antibodies generated utilizing defined monoclonal antibodies can act as surrogate antigens in the protection of infection in schistosomiasis.

Adjuvants for anti-parasite vaccines

To date the most successful human vaccines use attenuated living pathogens, but the advent of techniques in genetic engineering has meant that pure antigen can be provided in quantity. This has allowed the development of combined vaccines that use only the parasite antigens that convey protective immunity. However, isolated antigens lose immunogenicity so to regain potency, living attenuated carriers like Vaccinia or Salmonella can be used. To avoid the attendant drawbacks of carriers as immunopotentiating agents, adjuvants are under investigation as alternatives for use in vaccines against parasitic infections. In this review, Robert Bomford describes the adjuvants currently being examined for use in vaccines for both protozoan and helminth infections including Leishmania, malaria and Schistosoma. He also points out the drawbacks of using adjuvants and the dilemma of needing to stimulate cell'-mediated immunity while avoiding the immunopathological consequences of doing so.

Acquired immunity in schistosomiasis with purified Fasciola hepatica cross-reactive antigens

We have previously demonstrated that a Fasciola hepatica-derived adult worm antigen, which is cross-reactive with Schistosoma mansoni and designated FhSmIII(M), induces resistance to challenge infection with S. mansoni in mice. The current review concerns the methods developed to isolate and partially characterize a major component of FhSmIII(M), a 12-kDa polypeptide, as well as immunity studies involving this antigen. Utilizing conventional gel filtration, followed by diethylaminoethyl (DEAE) Sephadex A-120 and monitoring the fractions by polyacrylamide gel electrophoresis (PAGE) and enzyme-linked immunoelectrotransfer blot techniques (EITB), we were able to isolate the 12-kDa antigenic polypeptide to homogeneity. Conventional gel filtration chromatography was followed by high-pressure, liquid anion, exchange chromatography, when highly purified material was needed, although the effective yields diminished drastically with the latter. Mice, rabbits and calves with a primary infection of F. hepatica developed antibodies (detectable in enzyme linked immunosorbent assay (ELISA) to the F. hepatica 12-kDa polypeptide within 2 weeks of infection. Mice with a primary infection of S. mansoni developed significant, but low, levels of anti-12-kDa antibodies by 7 weeks post-infection. Immunization of mice with microgram amounts of this 12-kDa polypeptide in Freunds' adjuvant resulted in the development of up to 77% less S. mansoni worms than the controls. Treatment with either endoglycosidase H, neuraminidase or dithiothreitol had no effect on the protein's mobility on sodium dodecyl sulfate (SDS)-PAGE or in its recognition by antibodies, suggesting the absence of carbohydrate moieties or disulphide bonds in relation to its antigenic determinants. Degradation by proteinase K further confirmed its polypeptide nature and points to recombinant DNA technology for the large-scale manufacture of this potential vaccine. Further use of this antigen in immunity studies should greatly contribute to the clarification of the mechanisms involved in cross-resistance against schistosomiasis.

Progress in the development of vaccines against parasitic diseases

Vaccines for parasitic diseases have lagged behind the development of vaccines for important viral and bacterial diseases. Among the reasons for this is the extreme antigenic complexity of parasites and also the adaptive ability of parasites to co-exist with their host, often through modulation of the host's immune response. Advances in technology including in vitro cultivation, hybridoma and recombinant DNA methods have provided valuable tools for the study of parasite immunology and have resulted in major strides toward vaccines for several protozoan and helminth parasites.

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.

Schistosoma spp.: progress toward a defined vaccine

During the last 2 decades, much was learned concerning the nature of acquired immunity in schistosomiasis, under experimental as well as field conditions. The knowledge is being applied now to design of a defined vaccine against this major parasitic disease. Several Schistosoma spp. antigens have been purified and shown to potentially protect in vivo. Determination of a method for presenting these antigens that will induce an optimal combination of cellular and humoral immune responses remains a critical step in vaccine development.

Molecular cloning of a protective antigen of schistosomes

The complementary DNA sequence encoding the Mr 28,000 antigen of Schistosoma mansoni has been isolated and expressed in Escherichia coli. Experimental vaccination of rats, hamsters and monkeys with a recombinant fusion protein induces a strongly cytotoxic antibody response. Immunization of rats and hamsters with this protein leads to significant protection against a natural challenge infection with live cercariae.

Progress towards a defined vaccine for schistosomiasis

During the last five years considerable progress has been made in studies o f schistosome immunology. Convergent views have emerged from the study of human and animal immunity which agree on the mechanisms required and the antigens involved. The reproducible induction of protective immunity with attenuated parasites and with antigenic preparations has now led to agreement that vaccination against schistosomiosis is on achievable goal. The evidence that led to this optimistic view was reviewed at a scientific working group on 'Prospects for Immunological Intervention in Human Schistosomiosis' held in Geneva in May 1986, under the auspices of the UNDP/World Bonk/WHO Special Programme.

Identification of paramyosin as schistosome antigen recognized by intradermally vaccinated mice

Mice immunized intradermally with extracts of Schistosoma mansoni in combination with the adjuvant BCG are significantly protected against subsequent infection with living larval forms of the parasite. Remarkably, these vaccinated animals produce antibodies predominantly against a single parasite protein of molecular weight 97 kilodaltons (Sm-97). A complementary DNA that encodes about half of the Sm-97 molecule has now been cloned and sequenced. Analysis of the deduced amino acid sequence reveals a protein containing periodic repeats of hydrophobic amino acids characteristic of an alpha-helical coiled-coil structure. The deduced amino acid composition of the cloned gene and several properties of the native protein are similar to that of paramyosin, an alpha-helical protein that forms the core for myosin filaments in invertebrate muscle. Paramyosin was isolated from Schistosoma mansoni adult worms and antibodies to Sm-97 were shown to react with this molecule as well as with a known paramyosin from molluscan muscle.

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

Protective immunity has been demonstrated in experimental schistosomiasis and is also believed to occur in man. It can be mediated by antibodies from infected animals or animals immunized with attenuated organisms. Recombinant Escherichia coli synthesizing antigenic polypeptides from the three principal species of schistosome that infect man, Schistosoma mansoni, S. japonicum and S. haematobium, have been constructed. Libraries of adult worm cDNA were prepared from each species in the expression vector lambda gt 11 and directly screened with antibodies from animals experimentally immunized with S. mansoni and S. japonicum and from humans infected with S. haematobium. The S. mansoni clones have been analysed in greatest detail. At least four different types of clones were identified. All the detected recombinant polypeptide antigens were recognised by antibodies from chronically infected mice and most were also recognised by antibodies from mice immunized with attenuated cercariae and anti-surface membrane antibodies. Clones synthesizing species-specific antigens for both S. mansoni and S. japonicum were identified by simultaneous screening of both libraries. At least three types of S. haematobium clones were identified by screening with human infection serum, most of which were species-specific. All the antigens were in the form of fusion peptides with E. coli beta-galactosidase and their expression was induced by isopropylthiogalactopyranoside. Since known protective monoclonal antibodies recognise highly glycosylated membrane proteins which cannot be identified in the form of nascent polypeptides, the direct identification of polypeptide antigens defined by their reactivity, as reported here, is an essential step in producing reagents by recombinant DNA technology, suitable for vaccination and diagnosis.

Rat resistance to schistosomiasis: platelet-mediated cytotoxicity induced by C-reactive protein

In rats infected with the parasite Schistosoma mansoni, the concentration of C-reactive protein in the serum increases after the lung stage of infection and is at its highest at the time of terminal worm rejection. The peak of platelet-mediated cytotoxicity induced by infected serum that has been heated (and is free of immunoglobulin E) as well as the time course for the development of platelet cytotoxic activity in infected rats was found to be correlated with the concentration of C-reactive protein. Rat and human platelets treated with homologous serum obtained during an acute phase of inflammation or with purified C-reactive protein were able to kill the immature forms of the worm in vitro. Platelets treated with C-reactive protein were furthermore capable of conferring significant protection against schistosomiasis in transfer experiments. Collectively these data indicate that a system that includes C-reactive protein and platelets participates in the natural resistance of the rat to schistosomal infection.

Molecular cloning of schistosome genes

As part of an integrated programme investigating human schistosomiasis, work which involves epidemiological surveys and detailed immunological studies as well as biochemical investigations, we have, over the last three years, been cloning schistosome genes in a variety of plasmid and lambda vector systems. In this lecture we present a review of some selected aspects of work primarily aimed at production of experimental vaccines against the disease but which, on a broader front, is also concerned with developmental regulation of gene expression around the parasite's life-cycle. Specifically, we are interested in cloning three groups of genes. First, those encoding surface antigens; second, those associated with sexual maturity and egg production; and third, antigens which may provide a basis for a specific immunodiagnostic test.

Defined antigens secreted by the larvae of schistosomes protect against schistosomiasis: induction of cytotoxic antibodies in the rat and the monkey

The study of the immunology of schistosomiasis has allowed a clear understanding of the basic mechanisms of resistance, emphasizing the important role played by cellular and humoral factors. Whereas the production of polyclonal or monoclonal antibodies and the precise inventory of immune effector mechanisms in the rat and in man have led to the identification of potentially protective antigens, immunization with soluble schistosome components has not allowed a successful control of the destruction of schistosomula after infection. The experiments reported here show that schistosomulum-released products (SRP) were able to induce the production of antibodies, in the rat and the monkey, highly cytotoxic in antibody-dependent cellular cytotoxicity, using monocyte monolayers, platelets or eosinophils as effector cells. The immunization of rats with either total SRP or 25-30-kDa molecules purified from schistosomula conferred a significant protection towards a challenge infection by the parasite. IgE and to a lesser extent IgG antibodies represented the major humoral factors of cell activation leading to the schistosomulum killing when anti-SRP antisera, obtained after immunization of the monkey, were incubated with human effector cells.

Schistosoma mansoni surface glycoproteins. Analysis of their expression and antigenicity

Surface glycoproteins from newly transformed schistosomula of Schistosoma mansoni have been identified by surface radioiodination and lectin-affinity chromatography. From the glycoconjugates bound by the three lectins used, concanavalin A, peanut agglutinin and fucose-binding protein, only in the concanavalin-A-bound fractions were glycoproteins identified. Changes in concanavalin-A-binding glycoproteins were detected after transformation and early maturation of the schistosomula. Some glycoproteins disappeared (Mr 38 000, 29 000 and 25 000), some appeared independently of host molecules (Mr 19 000), others only appeared after culture in human serum (Mr 45 000). Two major glycoproteins of Mr 32 000 and 16 000 were detected on all stages examined. Within the total set of surface glycoproteins identified on 3-h schistosomula only the strong Mr-38 000-32 000 complex was found to be antigenic. Thus many major low-molecular-mass surface glycoproteins of the parasite are not recognised as antigens by immune animals. The separation of only the Mr-38 000-32 000 antigens by concanavalin A affinity chromatography indicates the feasibility of using this method in conjunction with immunoaffinity columns to purity these molecules.