Sm480: a high molecular weight Schistosoma mansoni antigen associated with protective immunity

Cross-Reactivity between Schistosoma mansoni Antigens and the Latex Allergen Hev b 7: Putative Implication of Cross-Reactive Carbohydrate Determinants (CCDs)

IgG antibodies produced by rabbits immunized against S. mansoni antigens cross-reacted with aqueous soluble constituents of a variety of allergens. The antibody cross-reactivity was largely sensitive to degradation by treatment of the target antigens with sodium meta-periodate, suggesting the cross-reactivity was due to carbohydrate determinants that were common to both the schistosome and the allergens (CCDs). The reaction between the rabbit antibodies and a 43 kDa molecule in a rubber latex extract was analysed further: tandem mass spectrometry identified the latex molecule as allergen Hev b 7. Rabbit anti-schistosome IgG antibodies purified by acid-elution from solid-phase latex Hev b 7 reacted with the S. mansoni egg antigens IPSE/alpha-1 and kappa-5 and cercarial antigens SPO-1 and a fatty acid-binding protein. Moreover, purified anti-S. mansoni egg, latex cross-reactive antibodies reacted with antigenic constituents of some fruits, a result of potential relevance to the latex-fruit syndrome of allergic reactions. We propose that IgG anti-schistosome antibodies that cross-react with allergens may be able to block IgE-induced allergic reactions and thus provide a possible explanation for the hygiene hypothesis.

A Vaccine for Schistosomiasis: alternative approaches

An independent trial of candidate antigens for a Schistosoma mansoni vaccine has been completed recently under the auspices of the World Health Organization TDR programme. It has been acknowledged that the results of the trial failed to meet expectations and, therefore, it is appropriate that the options for future work should be considered. In this article, Mike Doenhoff describes two S. mansoni molecules-a schistosome larval protease and a high molecular weight egg and worm antigen. Both are associated with protective immunity, but they have unusual immunological properties that distinguish them from the antigens tested so far. The results suggest that alternative approaches to a schistosomiasis vaccine are still worth exploring.

A Schistosoma japonicum chimeric protein with a novel adjuvant induced a polarized Th1 immune response and protection against liver egg burdens

Background

Schitosomiasis japonica is still a significant public health problem in China. A protective vaccine for human or animal use represents an important strategy for long-term control of this disease. Due to the complex life cycle of schistosomes, different vaccine design approaches may be necessary, including polyvalent subunit vaccines. In this study, we constructed four chimeric proteins (designated SjGP-1~4) via fusion of Sj26GST and four individual paramyosin fragments. We tested these four proteins as vaccine candidates, and investigated the effect of deviating immune response on protection roles in mice.

Methods

The immunogencity and protection efficacy of chimeric proteins were evaluated in mice. Next, the chimeric protein SjGP-3 was selected and formulated in various adjuvants, including CFA, ISA 206, IMS 1312 and ISA 70M. The titers of antigen-specific IgG, IgE and IgG subclass were measured. The effect of adjuvant on cytokine production and percentages of CD3⁺CD8^-IFN-γ⁺ cells and CD3⁺CD8^-IL-4⁺ cells were analyzed at different time points. Worm burdens and liver egg counts in different adjuvant groups were counted to evaluate the protection efficacy against cercarial challenge.

Results

Immunization of mice with chimeric proteins provided various levels of protection. Among the four proteins, SjGP-3 induced the highest level of protection, and showed enhanced protective efficacy compared with its individual component Sj26GST. Because of this, SjGP-3 was further formulated in various adjuvants to investigate the effect of adjuvant on immune deviation. The results revealed that SjGP-3 formulated in veterinary adjuvant ISA 70M induced a lasting polarized Th1 immune response, whereas the other adjuvants, including CFA, ISA 206 and IMS 1312, generated a moderate mixed Th1/Th2 response after immunization but all except for IMS 1312 shifted to Th2 response after onset of eggs. More importantly, the SjGP-3/70M formulation induced a significant reduction in liver egg deposition at 47.0–50.3% and the number of liver eggs per female at 34.5–37.2% but less effect on worm burdens at only 17.3–23.1%, whereas no effect of the formulations with other adjuvants on the number of liver eggs per female was observed.

Conclusion

Construction of polyvalent subunit vaccine was capable to enhance immunogenicity and protection efficacy against schistosomiasis. There was correlation of the polarized Th1 response with reduction of liver egg burdens, supporting the immune deviation strategy for schistosomiasis japonica vaccine development.

An association betweenSchistosoma mansoniworms and an enzymatically-active protease/peptidase in mouse blood

An enzyme found previously in extracts of adultSchistosoma mansoniworms, that hydrolysed the chromogenic substrate N-acetyl-DL-phenylalanine β-naphthyl-ester, has here been further investigated and characterized. Evidence that the molecule found in the parasite was antigenically and enzymatically homologous with a constituent of normal mouse plasma has been consolidated using a monospecific serum in immunoelectrophoresis and Western immunoblotting. The molecular size of the enzyme was found to be approximately 70 kDa and it was inhibited by a serine protease inhibitor, but not by inhibitors of other classes of protease. The enzymatic activity found in normal mouse serum was also found in normal rat serum, but not in sera from several other mammalian species.

Schistosoma japonicum: localization of calpain in the penetration glands and secretions of cercariae

A monoclonal antibody was generated against the large subunit of Schistosoma japonicum calpain to study the localization and possible function of the molecule in vivo. Mice were immunized with recombinant S. japonicum calpain and polyclonal antisera and a monoclonal antibody specific to schistosome calpain was obtained. In immunohistochemistry, a monoclonal antibody against S. japonicum calpain, KG-2E11, bound weakly to calpain expressed at the surface of adult worm tegument, however, it bound strongly to the cercarial secretions ("footprints") of S. japonicum, emitted from the penetration glands. The present study indicates that calpain is multifunctional as it is expressed at various locations in different developmental stages. Calpain-based vaccines could thus possibly induce protective immunity against cercariae and the following early developing stages.

The effects of immunization with recombinant Sm14 (rSm14) in reducing worm burden and mortality of mice infected with Schistosoma mansoni

To investigate whether mice immunization with the recombinant form of a 14.7 KDa Schistosoma mansoni protein (rSm14) confers protection against a S. mansoni lethal challenge infection, rSm14-immunized mice were challenged with different cercarial burdens. A significant protection was detected in immunized mice challenged with 100 or 1,000 S. mansoni cercariae when compared with their controls (p< 0.004 and p< 0.01 respectively). Differently from previous report, none of the mice from the control group (not immunized and infected with 1000 cercariae) died before the 30th day post-infection. A direct correlation between the number of challenge cercariae and the precocity of mice death was found. IgM anti-rSm14 antibodies were significantly produced (p< 0.05) mainly in the groups of immunized mice infected with 500 or 1000 cercariae. IgG and IgA anti-rSm14 antibodies were not significantly detected. In Western immunoblots, all mice sera showed a specific antibody response with a 14.7 KDa antigen being reacted with particular intensity in sera from immunized mice. The results show that immunization with rSm14 reduced mice worm burden independently of the cercariae load of challenge infection. No correlation was found between serum antibodies and worm burden reduction. In relation to cercarial load and the rate and precocity of mice mortality a direct correlation was found.

A fucose-containing epitope is shared by keyhole limpet haemocyanin and Schistosoma mansoni glycosphingolipids

The glycolipids of Schistosoma mansoni adult worms, cercariae and eggs are recognised by schistosome infection serum and the monoclonal antibody M2D3H. The haemocyanin of the keyhole limpet, Megathura crenulata, is known to be immunoreactive to schistosomal infection sera and is, therefore, under investigation for the diagnosis of and vaccination against schistosomiasis. By dot-blot, inhibition-ELISA and inhibition-HPTLC immunostaining we have demonstrated that the M2D3H epitope is shared by both S. mansoni glycolipids and keyhole limpet haemocyanin (KLH). Analogously to the established epitopic importance of fucose to the immunorecognition of S. mansoni glycolipids, we have similarly defined the significance of the fucose residue(s) for the immunoreactivity between KLH and schistosomal infection serum and the monoclonal antibody M2D3H. Fucose was specifically removed from KLH by partial hydrolysis, monitored by ultrafiltration and carbohydrate component analysis. On removal of the fucose residue(s) the serological and immunological reactivity of KLH was greatly diminished, which implied that the fucose-containing M2D3H antigenic determinant was common to both S. mansoni glycolipids and KLH.

Partial purification and characterization of Gastrothylax crumenifer somatic antigens

The soluble extracts of Gastrothylax crumenifer isolated from the rumen of buffalo (Bubalus bubalis) were fractionated on a Sephadex G-200 column. A total of eight major fractions (F1, F2, F3, F4, F5, F6, F7, and F8) were separated from the whole homogenate of G. crumenifer, and each of these fractions was tested for their antigenicity by ELISA against rabbit hyperimmune sera. It was observed that F1, F2, F3 and F4 were highly antigenic, F6 and F7 were moderately antigenic and F5 and F8 were poorly antigenic. The individual fractions analysed after SDS-PAGE and Western blotting indicated that the antigenic fractions of G. crumenifer are of low molecular weight, in the range of <14-50kDa, and predominant antigenic components which were evident in most of the Sephadex profiles were of Mr 15, 18, 19, 23-24 and 28-32kDa.

Cloning and molecular characterization of calpain, a calcium-activated neutral proteinase, from different strains of Schistosoma japonicum

cDNA coding for calpain of Schistosoma japonicum were cloned and sequenced, and serological basis of host responses to calpain were analyzed. cDNA of calpain from S. japonicum of two different isolates, Yamanashi strain (Sj-J) and Hunan strain (Sj-C), were 2, 468 bp and 2, 465 bp in length, including the same number (2, 274) of open reading frame. Nucleotide sequence and amino acid sequence between the two calpains are 99.1% and 98.8% identity, respectively. Sj-J and Sj-C calpains were considered to be translated as a preproenzyme, and a 746-amino acid mature enzyme contains eight motifs without a signal peptide at the N-terminal based on the deduced amino acid sequences. mRNA for calpain were detectable in different developmental stages, however, sera obtained from mice immunized with recombinant calpain showed enhanced binding to cercarial antigen. Human sera from S. japonicum-infected individuals recognized the large subunit of schistosomal calpain, and light-infected sera showed stronger reactivities to the recombinant calpain than moderate/high infection cases. When we tested synthetic peptides, there were four common human B cell epitopes in schistosomal calpain, all of which are shared with S. mansoni. Together with these results, calpain of S. japonicum seems to be not only a vaccine candidate, but also a target antigen for immunodiagnosis of human schistosomiasis.

Immunochemical characterisation of Schistosoma mansoni glycolipid antigens

The aim of this study was to investigate the occurrence, distribution and immunochemical properties of antibody-defined carbohydrate epitopes in neutral glycolipid fractions of Schistosoma mansoni eggs, cercariae and adults. The amount of extractable, antigenic, neutral glycolipids was lowest in adult worms, increasing consecutively in cercariae and eggs. The immunoreactivity of the glycolipids resided in the carbohydrate moiety in that it was periodate-sensitive. Serological reactivity, and monosaccharide component analysis, anomeric configuration and methylation-linkage analyses indicated that there were two dominant epitopes, which could be partially defined immunologically. The first epitope was detected on egg, cercarial and adult glycolipids. It was strongly recognised by mouse chronic infection sera and rabbit hyperimmune sera raised against specific egg antigens, and was defined by the monoclonal antibody M2D3H (Bickle QD, Andrews BJ. Characterisation of Schistosoma mansoni monoclonal antibodies which block in-vitro killing: failure to demonstrate blockage of immunity in vivo. Parasite Immunol 1988;10:151-168). M2D3H appeared to have the same epitope specificity as monoclonal antibody 128C3/3 (Weiss J, Magnani JL, Strand M. Identification of Schistosoma mansoni glycolipids that share immunogenic carbohydrate epitopes with glycoproteins. J Immunol. 1986;136:4275-82). The internal epitope was defined structurally by the presence of fucose 3-linked to 3,4-disubstituted N-acetylglucosamine, which was itself partially substituted by a second fucose residue, to yield the determinant -4[Fucalpha1,2Fucalpha3]GlcNAcbeta1-. The second epitope was defined by the anti-LewisX monoclonal antibody 4D1 and was found primarily on cercarial glycolipids. It was chemically characterised as the LewisX epitope of Galbeta1,4[Fucalpha1,3]GlcNAcbeta1- in a terminal position. The removal of fucose greatly diminished the binding of the anti-LewisX and M2D3H monoclonal antibodies, as well as the polyclonal chronic infection sera, to glycolipids of all three life-cycle stages and thus revealed the epitopic importance of fucose.

Proteinases and associated genes of parasitic helminths

Many parasites have deployed proteinases to accomplish some of the tasks imposed by a parasitic life style, including tissue penetration, digestion of host tissue for nutrition and evasion of host immune responses. Information on proteinases from trematodes, cestodes and nematode parasites is reviewed, concentrating on those worms of major medical and economical importance. Their biochemical characterization is discussed, along with their putative biological roles and, where available, their associated genes. For example, proteinases expressed by the various stages of the schistosome life-cycle, in particular the well-characterized cercarial elastase which is involved in the penetration of the host skin and the variety of proteinases, such as cathepsin B (Sm31), cathepsin L1, cathepsin L2, cathepsin D, cathepsin C and legumain (Sm32), which are believed to be involved in the catabolism of host haemoglobin. The various endo- and exoproteinases of Fasciola hepatica, the causative agent of liver fluke disease, are reviewed, and recent reports of how these enzymes have been successfully employed in cocktail vaccines are discussed. The various proteinases of cestodes and of the diverse superfamilies of parasitic nematodes are detailed, with special attention being given to those parasites for which most is known, including species of Taenia, Echinococcus, Spirometra, Necator, Acylostoma and Haemonchus. By far the largest number of papers in the literature and entries to the sequence data bases dealing with proteinases of parasitic helminths report on enzymes belonging to the papain superfamily of cysteine proteinases. Accordingly, the final section of the review is devoted to a phylogenetic analysis of this superfamily using over 150 published sequences. This analysis shows that the papain superfamily can be divided into two major branches. Branch A contains the cathepin Bs, the cathepsin Cs and a novel family termed cathepsin Xs, while Branch B contains the cruzipains, cathepsin Ls, papain-like and aleurain/cathepsin H-like proteinases. The relationships of the helminth proteinases, and similar proteinases from protozoan parasites and other organisms, within these groups are discussed.