Differences in immunogenicity and vaccine potential of peptides from Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase

Differential protective impact of peptide vaccine formulae targeting the lung- and liver-stage of challenge Schistosoma mansoni infection in mice

The study aimed to elicit protective immune responses against murine schistosomiasis mansoni at the parasite lung- and liver stage. Two peptides showing amino acid sequence similarity to gut cysteine peptidases, which induce strong memory immune effectors in the liver, were combined with a peptide based on S. mansoni thioredoxin peroxidase (TPX), a prominent lung-stage schistosomula excretory-secretory product, and alum as adjuvant. Only one of the 2 cysteine peptidases-based peptides in a multiple antigenic peptide construct (MAP-3 and MAP-4) appeared to adjuvant protective immune responses induced by the TPX peptide in a MAP form. Production of TPX MAP-specific IgG1 serum antibodies, and increase in lung interleukin-1 (IL-1), uric acid, and reactive oxygen species (ROS) content were associated with significant (P < 0.05) 50 % reduction in recovery of lung-stage larvae. Increase in lung triglycerides and cholesterol levels appeared to provide the surviving worms with nutrients necessary for a stout double lipid bilayer barrier at the parasite-host interface. Surviving worms-released products elicited memory responses to the MAP-3 immunogen, including production of specific IgG1 antibodies and increase in liver IL-33 and ROS. Reduction in challenge worm burden recorded 45 days post infection did not exceed 48 % associated with no differences in parasite egg counts in the host liver and small intestine compared to unimmunized adjuvant control mice. Alum adjuvant assisted the second peptide, MAP-4, in production of IgG1, IgG2a, IgG2b and IgA specific antibodies and increase in liver ROS, but with no protective potential, raising doubt about the necessity of adjuvant addition. Accordingly, different vaccine formulas containing TPX MAP and 1, 2 or 3 cysteine peptidases-derived peptides with or without alum were used to immunize parallel groups of mice. Compared to unimmunized control mice, significant (P < 0.05 to < 0.005) 22 to 54 % reduction in worm burden was recorded in the different groups associated with insignificant changes in parasite egg output. The results together indicated that a schistosomiasis vaccine able to entirely prevent disease and halt its transmission still remains elusive.

GLYCOLYTIC ENZYMES AS VACCINES AGAINST SCHISTOSOMIASIS: TESTING SCHISTOSOMA MANSONI PHOSPHOGLYCERATE MUTASE IN MICE

Schistosomiasis is a globally burdensome parasitic disease caused by flatworms (blood flukes) in the genus Schistosoma. The current standard treatment for schistosomiasis is the drug praziquantel, but there is an urgent need to advance novel interventions such as vaccines. Several glycolytic enzymes have been evaluated as vaccine targets for schistosomiasis, and data from these studies are reviewed here. Although these parasites are canonically considered to be intracellular, proteomic analysis has revealed that many schistosome glycolytic enzymes are additionally found at the host-interactive surface. We have recently found that the intravascular stage of Schistosoma mansoni (Sm) expresses the glycolytic enzyme phosphoglycerate mutase (PGM) on the tegumental surface. Live parasites display PGM activity, and suppression of PGM gene expression by RNA interference diminishes surface enzyme activity. Recombinant SmPGM (rSmPGM) can cleave its glycolytic substrate, 3-phosphoglycerate and can both bind to plasminogen and promote its conversion to an active form (plasmin) in vitro, suggesting a moonlighting role for this enzyme in regulating thrombosis in vivo. We found that antibodies in sera from chronically infected mice recognize rSmPGM. We also tested the protective efficacy of rSmPGM as a vaccine in the murine model. Although immunization generates high titers of anti-SmPGM antibodies (against both recombinant and native SmPGM), no significant differences in worm numbers were found between vaccinated and control animals.

Proteomic analysis of Taenia solium cysticercus and adult stages

Taenia solium (T. solium) cysticercosis is a neglected parasitic zoonosis that occurs in developing countries. Since T. solium has a complex life cycle that includes eggs, oncospheres, cysticerci, and adults, presumably many proteins are produced that enable them to survive and establish an infection within the host. The objectives of this study were to perform a comparative proteomic analysis of two ontogenetic stages of T. solium (cysticerci and adult) and to analyze their differential expression of proteins. Methods proteins were separated by High Performance Liquid Chromatography (HPLC) fractionation, and protein samples were also digested in liquid and identified by liquid chromatography tandem mass spectrometry (LC-MS/MS); the differentially expressed proteins were then processed by a bioinformatics analysis and verified by parallel reaction monitoring (PRM). Results we identified 2,481 proteins by label-free quantitative proteomics. Then differentially expressed proteins were screened under P values < 0.05 and 2 fold change, we found that 293 proteins up-regulated and 265 proteins down-regulated. Discussion through the bioinformatics analysis, we analyzed the differences types and functions of proteins in the Taenia solium and cysticercus, the data will provide reference value for studying the pathogenic mechanism of the two stages and the interaction with the host, and also support for further experimental verification.

A comprehensive and critical overview of schistosomiasis vaccine candidates

A digenetic platyhelminth Schistosoma is the causative agent of schistosomiasis, one of the neglected tropical diseases that affect humans and animals in numerous countries in the Middle East, sub-Saharan Africa, South America and China. Several control methods were used for prevention of infection or treatment of acute and chronic disease. Mass drug administration led to reduction in heavy-intensity infections and morbidity, but failed to decrease schistosomiasis prevalence and eliminate transmission, indicating the need to develop anti-schistosome vaccine to prevent infection and parasite transmission. This review summarizes the efficacy and protective capacity of available schistosomiasis vaccine candidates with some insights and future prospects.

Does Curcumin Have a Role in the Interaction between Gut Microbiota and Schistosoma mansoni in Mice?

There is strong correlation between changes in abundance of specific bacterial species and several diseases including schistosomiasis. Several studies have described therapeutic effects of curcumin (CUR) which may arise from its regulative effects on intestinal microbiota. Thus, we examined the impact of CUR on the diversity of intestinal microbiota with/without infection by Schistosoma mansoni cercariae for 56 days. Enterobacteriaceae was dominating in a naive and S. mansoni infected mice group without CUR treatment, the most predominant species was Escherichia coli with relative density (R.D%) = 80.66% and the least one was Pseudomonas sp. (0.52%). The influence of CUR on murine microbiota composition was examined one week after oral administration of high (40) and low (20 mg/kg b.w.) CUR doses were administered three times, with two day intervals. CUR induced high variation in the Enterobacteriaceae family, characterized by a significant (p < 0.001) reduction in E. coli and asignificant (p < 0.001) increase in Pseudomonas sp. in both naïve and S. mansoni-infected mice, compared to untreated mice, in a dose-dependent manner. Additionally, our study showed the effects of high CUR doses on S. mansoni infection immunological and parasitological parameters. These data support CUR’s ability to promote Pseudomonas sp. known to produce schistosomicidal toxins and offset the sequelae of murine schistosomiasis.

A Multiple Antigen Peptide Vaccine Containing CD4+ T Cell Epitopes Enhances Humoral Immunity against Trichinella spiralis Infection in Mice

Multiepitope peptide vaccine has some advantages over traditional recombinant protein vaccine due to its easy and fast production and possible inclusion of multiple protective epitopes of pathogens. However, it is usually poorly immunogenic and needs to conjugate to a large carrier protein. Peptides conjugated to a central lysine core to form multiple antigen peptides (MAPs) will increase the immunogenicity of peptide vaccine. In this study, we constructed a MAP consisting of CD4⁺ T cell and B cell epitopes of paramyosin (Pmy) of Trichinella spiralis (Ts-Pmy), which has been proved to be a good vaccine candidate in our previous work. The immunogenicity and induced protective immunity of MAP against Trichinella spiralis (T. spiralis) infection were evaluated in mice. We demonstrated that mice immunized with MAP containing CD4⁺ T cell and B cell epitopes (MAP-TB) induced significantly higher protection against the challenge of T. spiralis larvae (35.5% muscle larva reduction) compared to the MAP containing B cell epitope alone (MAP-B) with a 12.4% muscle larva reduction. The better protection induced by immunization of MAP-TB was correlated with boosted antibody titers (both IgG1 and IgG2a) and mixed Th1/Th2 cytokine production secreted by the splenocytes of immunized mice. Further flow cytometry analysis of lymphocytes in spleens and draining lymph nodes demonstrated that mice immunized with MAP-TB specifically enhanced the generation of T follicular helper (Tfh) cells and germinal center (GC) B cells, while inhibiting follicular regulatory CD4⁺ T (Tfr) cells and regulatory T (Treg) cells. Immunofluorescence staining of spleen sections also confirmed that MAP-TB vaccination enhanced the formation of GCs. Our results suggest that CD4⁺ T cell epitope of Ts-Pmy is crucial in vaccine component for inducing better protection against T. spiralis infection.

Why Do Intravascular Schistosomes Coat Themselves in Glycolytic Enzymes?

Schistosomes are intravascular parasitic helminths (blood flukes) that infect more than 200 million people globally. Proteomic analysis of the tegument (skin) of these worms has revealed the surprising presence of glycolytic enzymes on the parasite's external surface. Immunolocalization data as well as enzyme activity displayed by live worms confirm that functional glycolytic enzymes are indeed expressed at the host-parasite interface. Since these enzymes are traditionally considered to function intracellularly to drive glycolysis, in an extracellular location they are hypothesized to engage in novel "moonlighting" functions such as immune modulation and blood clot dissolution that promote parasite survival. For instance, several glycolytic enzymes can interact with plasminogen and promote its activation to the thrombolytic plasmin; some can inhibit complement function; some induce B cell proliferation or macrophage apoptosis. Several pathogenic bacteria and protists also express glycolytic enzymes externally, suggesting that moonlighting functions of extracellular glycolytic enzymes can contribute broadly to pathogen virulence. Also see the video abstract here https://youtu.be/njtWZ2y3k_I.

Identification of common immunodominant antigens of Eimeria tenella, Eimeria acervulina and Eimeria maxima by immunoproteomic analysis

Clinical chicken coccidiosis is mostly caused by simultaneous infection of several Eimeria species, and host immunity against Eimeria is species-specific. It is urgent to identify common immunodominant antigen of Eimeria for developing multivalent anticoccidial vaccines. In this study, sporozoite proteins of Eimeria tenella, Eimeria acervulina and Eimeria maxima were analyzed by two-dimensional electrophoresis (2DE). Western bot analysis was performed on the yielded 2DE gel using antisera of E. tenella E. acervulina and E. maxima respectively. Next, the detected immunodominant spots were identified by comparing the data from MALDI-TOF-MS/MS with available databases. Finally, Eimeria common antigens were identified by comparing amino acid sequence between the three Eimeria species. The results showed that analysis by 2DE of sporozoite proteins detected 629, 626 and 632 protein spots from E. tenella, E. acervulina and E. maxima respectively. Western bot analysis revealed 50 (E. tenella), 64 (E. acervulina) and 57 (E. maxima) immunodominant spots from the sporozoite 2DE gels of the three Eimeria species. The immunodominant spots were identified as 33, 27 and 25 immunodominant antigens of E. tenella, E. acervulina and E. maxima respectively. Fifty-four immunodominant proteins were identified as 18 ortholog proteins among the three Eimeria species. Finally, 5 of the 18 ortholog proteins were identified as common immunodominant antigens including elongation factor 2 (EF-2), 14-3-3 protein, ubiquitin-conjugating enzyme domain-containing protein (UCE) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In conclusion, our results not only provide Eimeria sporozoite immunodominant antigen map and additional immunodominant antigens, but also common immunodominant antigens for developing multivalent anticoccidial vaccines.

Papain-Based Vaccination Modulates Schistosoma mansoni Infection-Induced Cytokine Signals

We have previously shown that immunization of outbred rodents with cysteine peptidases-based vaccine elicited type 2-biased immune responses associated with consistent and reproducible protection against challenge Schistosoma mansoni. We herein start to elucidate the molecular basis of C57BL/6 mouse resistance to S. mansoni following treatment with the cysteine peptidase, papain. We evaluated the early cytokine signals delivered by epidermal, dermal, and draining lymph node cells of naïve, and S. mansoni -infected mice treated 1 day earlier with 0 or 50 μg papain, or immunized twice with papain only (10 μg/mouse), papain-free recombinant S. mansoni glyceraldehyde 3-phosphate dehydrogenase and 2-Cys peroxiredoxin peptide (10 and 15 μg/mouse, respectively = antigen Mix), or papain-adjuvanted antigen Mix. Schistosoma mansoni infection induced epidermal and lymph node cells to release type 1, type 2 and type 17 cytokines, known to counteract each other. Expectedly, humoral immune responses were negligible until patency. Papain pretreatment or papain-based vaccination diminished or shut off S. mansoni infection early induction of type 1, type 17 and type 2 cytokines except for thymic stromal lymphopoietin and programmed the immune system towards a polarized type 2 immune milieu, associated with highly significant (P < 0.005 - <0.0001) resistance to S. mansoni infection.

Why the radiation-attenuated cercarial immunization studies failed to guide the road for an effective schistosomiasis vaccine: A review

Schistosomiasis is a debilitating parasitic disease caused by platyhelminthes of the genus Schistosoma, notably Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum. Pioneer researchers used radiation-attenuated (RA) schistosome larvae to immunize laboratory rodent and non-human primate hosts. Significant and reproducible reduction in challenge worm burden varying from 30% to 90% was achieved, providing a sound proof that vaccination against this infection is feasible. Extensive histopathological, tissue mincing and incubation, autoradiographic tracking, parasitological, and immunological studies led to defining conditions and settings for achieving optimal protection and delineating the resistance underlying mechanisms. The present review aims to summarize these findings and draw the lessons that should have guided the development of an effective schistosomiasis vaccine.

Biochemical characterisation of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) from the liver fluke, Fasciola hepatica

Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) catalyses one of the two steps in glycolysis which generate the reduced coenzyme NADH. This reaction precedes the two ATP generating steps. Thus, inhibition of GAPDH will lead to substantially reduced energy generation. Consequently, there has been considerable interest in developing GAPDH inhibitors as anti-cancer and anti-parasitic agents. Here, we describe the biochemical characterisation of GAPDH from the common liver fluke Fasciola hepatica (FhGAPDH). The primary sequence of FhGAPDH is similar to that from other trematodes and the predicted structure shows high similarity to those from other animals including the mammalian hosts. FhGAPDH lacks a binding pocket which has been exploited in the design of novel antitrypanosomal compounds. The protein can be expressed in, and purified from Escherichia coli; the recombinant protein was active and showed no cooperativity towards glyceraldehyde 3-phosphate as a substrate. In the absence of ligands, FhGAPDH was a mixture of homodimers and tetramers, as judged by protein-protein crosslinking and analytical gel filtration. The addition of either NAD⁺ or glyceraldehyde 3-phosphate shifted this equilibrium towards a compact dimer. Thermal scanning fluorimetry demonstrated that this form was considerably more stable than the unliganded one. These responses to ligand binding differ from those seen in mammalian enzymes. These differences could be exploited in the discovery of reagents which selectively disrupt the function of FhGAPDH.

Cysteine peptidases as schistosomiasis vaccines with inbuilt adjuvanticity

Schistosomiasis is caused by several worm species of the genus Schistosoma and afflicts up to 600 million people in 74 tropical and sub-tropical countries in the developing world. Present disease control depends on treatment with the only available drug praziquantel. No vaccine exists despite the intense search for molecular candidates and adjuvant formulations over the last three decades. Cysteine peptidases such as papain and Der p 1 are well known environmental allergens that sensitize the immune system driving potent Th2-responses. Recently, we showed that the administration of active papain to mice induced significant protection (P<0.02, 50%) against an experimental challenge infection with Schistosoma mansoni. Since schistosomes express and secrete papain-like cysteine peptidases we reasoned that these could be employed as vaccines with inbuilt adjuvanticity to protect against these parasites. Here we demonstrate that sub-cutaneous injection of functionally active S. mansoni cathepsin B1 (SmCB1), or a cathepsin L from a related parasite Fasciola hepatica (FhCL1), elicits highly significant (P<0.0001) protection (up to 73%) against an experimental challenge worm infection. Protection and reduction in worm egg burden were further increased (up to 83%) when the cysteine peptidases were combined with other S. mansoni vaccine candidates, glyceraldehyde 3-phosphate dehydrogenase (SG3PDH) and peroxiredoxin (PRX-MAP), without the need to add chemical adjuvants. These studies demonstrate the capacity of helminth cysteine peptidases to behave simultaneously as immunogens and adjuvants, and offer an innovative approach towards developing schistosomiasis vaccines

Novel therapeutic and prevention approaches for schistosomiasis: review

Schistosomiasis is a debilitating disease affecting approximately 600 million people in 74 developing countries, with 800 million, mostly children at risk. To circumvent the threat of having praziquantel (PZQ) as the only drug used for treatment, several PZQ derivatives were synthesized, and drugs destined for other parasites were used with success. A plethora of plant-derived oils and extracts were found to effectively kill juvenile and adult schistosomes, yet none was progressed to pre- and clinical studies except an oleo-gum resin extracted from the stem of Commiphora molmol, myrrh, which action was challenged in several trials. We have proposed an essential fatty acid, a component of our diet and cells, the polyunsaturated fatty acid arachidonic acid (ARA) as a remedy for schistosomiasis, due to its ability to activate the parasite tegument-bound neutral sphingomyelinase, with subsequent hydrolysis of the apical lipid bilayer sphingomyelin molecules, allowing access of specific antibody molecules, and eventual worm attrition. This concept was convincingly supported using larval and adult Schistosoma mansoni and Schistosoma haematobium worms in in vitro experiments, and in vivo studies in inbred mice and outbred hamsters. Even if ARA proves to be an entirely effective and safe therapy for schistosomiasis, it will not prevent reinfection, and accordingly, the need for developing an effective vaccine remains an urgent priority. Our studies have supported the status of S. mansoni calpain, glutathione-S-transferase, aldolase, triose phosphate isomerase, glyceraldehyde 3-phosphate dehydrogenase, enolase, and 2-cys peroxiredoxin as vaccine candidates, as they are larval excreted-secreted products and, contrary to the surface membrane molecules, are entirely accessible to the host immune system effector elements. We have proposed that the use of these molecules, in conjunction with Th2 cytokines-inducing adjuvants for recruiting and activating eosinophils and basophils, will likely lead to development and implementation of a sterilizing vaccine in a near future.

Enzymatic activity and immunolocalization of Schistosoma mansoni and Schistosoma haematobium neutral sphingomyelinase

We predicted, and provided evidence for, the existence of a schistosome tegument-associated Mg(2+)-dependent neutral sphingomyelinase (nSMase), which controls hydrolysis of surface membrane sphingomyelin molecules, thus allowing nutrients, but not host antibodies, to access proteins at the host-parasite interface. While a putative nSMase was identified in a recent Schistosoma mansoni genome sequencing and analysis study, our report is the first to measure nSMase enzymatic activity in Triton X-100-solubilized surface membrane (Sup 1) and whole worm soluble (SWAP) molecules of male and female S. mansoni and Schistosoma haematobium. Neutral, but no acidic, sphingomyelinase activity was readily detectable by the amplex red sphingomyelinase assay, and increased with incubation time and protein amount. Like nSMase family members, the schistosome nSMase activity was significantly (P<0.05 to <0.0001) enhanced by unsaturated fatty acids and phosphatidyl serine and significantly (P<0.01) decreased following exposure to the nSMase specific inhibitor GW4869. Peptides based on the published sequence of S. mansoni putative nSMase and used in a multiple antigen peptide form induced the generation of specific antibodies, which readily bound to the immunogen and to the cognate protein in Sup 1 and SWAP. Immunofluorescence studies suggested the parasite nSMase is located in the worm tegument and gut lining. Studies using RNA interference are in progress to define nSMase role in larval and adult worm surface membrane antigen exposure and unsaturated fatty acid-mediated attrition.

Role of antibodies in Sm-p80-mediated protection against Schistosoma mansoni challenge infection in murine and nonhuman primate models

Schistosomiasis is an important public health concern in more than 76 developing countries. Advent of an anti-schistosome vaccine would undoubtedly add to the existing control measures and may eventually help in the elimination of this disease. In the present study we have attempted to dissect the role(s) of antibodies in Sm-p80 mediated protection by intravenously transferring pooled sera from mice immunized with Sm-p80-pcDNA3 or purified IgG from baboons immunized with Sm-p80-pcDNA3, into naïve C57BL/6 mice, respectively, prior to challenge with cercariae. The passive transfer of antibodies from protected mice (homologous transfers) as well as transfer of total IgG from baboons (heterologous transfers), into naïve mice showed statistically significant reductions in worm burden and in the number of eggs in the tissues. Immunizations of antibody knockout mice (μMt-/-; B10.129S2 (B6)-Igh-6(tm1Cgn)/J) with recombinant Sm-p80 in the presence of CpG-motif oligodeoxynucleotides as an adjuvant, resulted in substantial reduction of Sm-p80-mediated protection, compared to C57BL/6 (normal) control group of mice. Down regulation of cytokines that have important effects on B cell proliferation as well as the recovery of higher number of parasites in antibody knockout indicated a significant role(s) of antibodies in Sm-p80-mediated protection against Schistosoma mansoni in mice. In toto, these studies appear to suggest that antibodies play a significant role in Sm-p80 mediated protection.

Schistosoma mansoni ex vivo lung-stage larvae excretory-secretory antigens as vaccine candidates against schistosomiasis

Schistosoma mansoni lung-stage larvae are known to be the major target of innate and acquired immunity to schistosomiasis. Lung schistosomula cytosolic or surface membrane antigens are hidden, entirely inaccessible to the host immune system, and hence are not particularly important as vaccine candidates. Conversely, excretory-secretory (E-S) products released from intact, viable, elongated, and contractile schistosomula are ideal potential vaccines, as such molecules can readily play a central role in the induction of local primary and memory immune response effectors that would directly target, surround, and pursue the larvae while negotiating the lung capillaries. Therefore, 6-day-old ex vivo larvae were isolated from mouse or hamster lung cells and used for generation of E-S products, which were shown to elicit strong immune responses and significant (P<0.05) protection against challenge infection in BALB/c mice. Proteomic analysis of E-S molecules following 10x concentration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis identified peptides related to innumerable host and about 15 S. mansoni-specific proteins. Selected S. mansoni-specific E-S peptides prepared in a multiple antigen peptide (MAP) or recombinant form were shown to stimulate considerable specific antibody response and peripheral blood mononuclear cell expression of mRNA for several cytokines in immunized C57BL/6 and BALB/c mice. However, highly significant (P<0.05 to <0.005) reduction in challenge infection worm burden and egg load was recorded only when the immunization conditions in test mice provided the S. mansoni antigen-specific T helper (Th) type response milieu favorable for each immunogen. That was polarized Th1 for S. mansoni aldolase and thioredoxin peroxidase 1 MAPs, polarized Th2 for recombinant 14-3-3-like protein, mixed Th1/Th17 for calpain MAP, and mixed Th1/Th2 for recombinant p18 protein. The findings together indicated that the immune responses issue is as critical as the nature and source of the antigen for the development of vaccine against schistosomiasis.

Experimental vaccines in animal models for schistosomiasis

Considerable morbidity and mortality results from the affliction of an estimated 200 million people worldwide by several species of schistosomes; 779 million are exposed to the disease in 74 different countries. Even though anti-parasitic drugs and other control measures, including public hygiene and snail control are available, the advent of an effective vaccine still remains the most potentially powerful means for the control of this disease. The putative vaccine could be administered to small children prior to the time when their contact with infected water is maximal, so as to prevent severe infection in the subsequent years. This review attempts to summarize the status of schistosome vaccine development with special emphasis on functionally important vaccine candidates. The importance of utilizing both murine and nonhuman primate models as a prerequisite for clinical trials is discussed.

Praziquantel binds Schistosoma mansoni adult worm actin

Praziquantel (PZQ) is widely used for the treatment of schistosomiasis. It induces worm muscle contractions and tegumental disruption, followed by exposure of parasite surface membrane antigens to the host immunological defence mechanisms. It may be assumed that PZQ, like cholesterol, is too hydrophobic to traverse the schistosome outer lipid bilayers by passive diffusion and probably requires binding to a surface membrane protein carrier for distribution throughout the worm. However, the PZQ binding site on the schistosome surface and the precise mechanism of action are not yet known. The Claisen condensation reaction was used to bind PZQ on cellulose acetate membranes. Triton-insoluble surface membrane antigens of Schistosoma mansoni adult worms were allowed to bind to the PZQ column. The identity of the bound molecules was examined by amino acid microsequencing and immunogenicity in outbred and inbred mice. The PZQ column was found to bind molecules of 45 kDa selectively from the Triton-insoluble surface membrane antigens of S. mansoni adult worms. Amino acid microsequencing revealed that the 45 kDa species consist predominantly of schistosome actin. This finding was supported by the poor immunogenicity of the 45 kDa molecules in outbred and inbred mice. PZQ was also shown to bind bovine actin but not bovine serum albumin. However, pre-incubation with bovine actin did not impair the effect of PZQ on adult worms in vitro. The study represents an attempt to understand how PZQ distributes across schistosome outer lipid bilayers.

Equilibrium in lung schistosomula sphingomyelin breakdown and biosynthesis allows very small molecules, but not antibody, to access proteins at the host-parasite interface

The mechanism by which lung-stage schistosomula expose proteins at the host-parasite interface to nutrient, but not antibody, uptake has been obscure. We have found that Schistosoma mansoni and Schistosoma haematobium larvae emerging from host lung at a pH of around 7.5, and fixed with diluted formaldehyde (HCHO), readily bind specific antibodies in indirect membrane immunofluorescence. Data on inhibitors and activators of parasite tegument-bound, magnesium-dependent, neutral sphingomyelinase (nSMase), and sphingomyelin biosynthesis inhibitors revealed that equilibrium in schistosomular sphingomyelin breakdown and biosynthesis prevents antibody binding, yet permits access of small HO-CH2-OH polymers to interact with and cross-link proteins at the host-parasite interface, allowing for their serological visualization.

Influence of interleukin-2 and interferon-gamma in murine schistosomiasis

Schistosoma mansoni-infected mice were administered at the time of parasite residency in the lung with recombinant murine interleukin (IL)-2 or interferon-gamma (IFN-gamma), to evaluate the impact of cytokines in host responses to primary schistosomiasis. S. mansoni lung-stage schistosomula did not affect plasma lipids levels in BALB/c, while elicited significant (p<0.05) increase in free fatty acids (FA) and decrease in cholesterol plasma levels in C57BL/6 and CD1 mice, and stimulated expression of mRNA for Th2 cytokines in BALB/c and Th1 cytokines in C57BL/6 and CD1 mice. Production of specific antibodies was negligible in the 3 strains. Interleukin-2 treatment elicited significant (p<0.001) decrease in triglycerides (TG) in CD1, and decrease in TG and cholesterol plasma levels and down-regulation of TNF-alpha mRNA expression in C57BL/6 mice. Induction of type 2 cytokines and/or IFN-gamma mRNA expression did not lead to increase in percentage of specific antibody responders in any mouse strain. Exogenous IL-2-related reduction in cholesterol plasma levels and TNF-alpha mRNA expression in C57BL/6 mice was associated with significant (p<0.05) decrease in adult worm recovery and egg count. Treatment with IFN-gamma elicited significant (p<0.05) free FA plasma levels increase in BALB/c and C57BL/6 and decrease in CD1 mice. Expression of type 2 cytokines mRNA was stimulated in BALB/c and CD1 mice, yet was not accompanied with increase in humoral responses. Exogenous IFN-gamma-related reduction in free FA plasma levels and IFN-gamma mRNA response, and up-regulation of TNF-alpha mRNA expression in CD1 mice were associated with significant increase in adult worm burden and egg load. The data were discussed in an attempt to define host factors predictive of resistance to schistosome infection.

Identification of paramyosin T cell epitopes associated with human resistance to Schistosoma mansoni reinfection

Paramyosin, a Schistosoma mansoni myoprotein associated with human resistance to infection and reinfection, is a candidate antigen to compose a subunit vaccine against schistosomiasis. In this study, 11 paramyosin peptides selected by TEPITOPE algorithm as promiscuous epitopes were produced synthetically and tested in proliferation and in vitro human leucocyte antigen (HLA)-DR binding assays. A differential proliferative response was observed in individuals resistant to reinfection compared to individuals susceptible to reinfection in response to Para (210-226) peptide stimulation. In addition, this peptide was able to bind to all HLA-DR molecules tested in HLA-DR binding assays, confirming its promiscuity. Para (6-22) and Para (355-371) were also shown to be promiscuous peptides, because they were able to bind to the six and eight most prevalent HLA-DR alleles used in HLA-DR binding assays, respectively, and were also recognized by T cells of the individuals studied. These results suggest that these paramyosin peptides are promising antigens to compose an anti-schistosomiasis vaccine.

Human T cell epitope mapping of the Schistosoma mansoni 14-kDa fatty acid-binding protein using cells from patients living in areas endemic for schistosomiasis

The development of a defined anti-schistosomiasis vaccine would contribute to the current control strategy mainly because immunization provides long-lasting immunity to the disease. Sm14, one of the six Schistosoma mansoni antigens selected by WHO as a candidate to compose a subunit vaccine against schistosomiasis, has been associated with resistance to S. mansoni infection in human beings and is able to induce protection in the murine model. To identify human T cell epitopes in Sm14, we used the TEPITOPE algorithm to select peptides that would most likely bind to several HLA-DR molecules. In this study, three Sm14 epitopes were selected and produced as synthetic peptides. Human T cell responses from schistosomiasis patients living in endemic areas in Brazil were determined by proliferation assay and IL-5 and IFN-gamma measurements. Differential peptide recognition and cytokine production in response to Sm14 epitopes were observed in individuals resistant to S. mansoni infection versus susceptible individuals. Sm14(32-48) and Sm14(53-69) peptides were preferentially recognized by peripheral blood mononuclear cells (PBMCs) of S. mansoni-resistant individuals, and Sm14(53-69) induced significant production of IFN-gamma. Additionally, Sm14(32-48) and Sm14(53-69) were "promiscuous" peptides, since they were able to induce cellular immune responses in individuals carrying 10 and 8, respectively, of the 11 HLA-DR molecules expressed in the studied population. Among Sm14 synthetic peptides tested in this study, we identified Sm14(32-48) and Sm14(53-69) as promising candidates to compose an anti-schistosomiasis vaccine, since they seem to be related to resistance to human schistosomiasis.

Cloning, characterization and DNA immunization of an Onchocerca volvulus glyceraldehyde-3-phosphate dehydrogenase (Ov-GAPDH)

In the search for Onchocerca volvulus antigens possibly involved in protection against human onchocerciasis, partial amino acid sequence analysis of one of the O. volvulus antigens of the serologically identified proteins showed a close relationship to the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) protein family. Subsequent adult worm cDNA library screening and cloning produced a clone of 1650 bp. An open reading frame spans over 1020 bp encoding for a protein of 340 amino acids with an apparent molecular weight of 38000. Comparison of the complete amino acid sequence identified this protein as a member of the GAPDH protein family. The recombinantly expressed protein shows GAPDH enzymatic activity as well as plasminogen-binding capacity. DNA sequence analysis of the corresponding gene revealed the presence of two introns. Using immunohistology Ov-GAPDH was observed in microfilariae, infective larvae, and adult male and female worms. Most striking was the labelling of the musculature of the body wall. Labelling was also observed in the pseudocoeloma cavity and in a subset of cell nuclei, suggesting additional, non-glycolytic functions of the Ov-GAPDH. Gene gun immunization with the DNA-construct in cattle led to specific humoral immune responses. Thus, the protective potential of the DNA-construct of Ov-GAPDH can be evaluated in vaccination trials using animal models such as the cattle/Onchocerca ochengi model.

Peptide dendrimers

Dendrimers are branched structures and represent a fast growing field covering many areas of chemistry. Various types of dendrimers differing in composition and structure are mentioned, together with their practical use spanning from catalysis, transport vehicles to synthetic vaccines. The main stress is given to peptide dendrimers, namely, multiple antigenic peptides (MAPs). Their synthesis, physicochemical properties, biological activities, etc. have been described with many examples. MAPs can be used as diagnostics, mimetics, for complexation of different cations, as vaccines against parasites, bacteria, viruses, etc.

Identification of immunodominant epitopes of Schistosoma mansoni vaccine candidate antigens using human T cells

Paramyosin and Sm14 are two of the six antigens selected by the World Health Organization as candidates to compose a subunit vaccine against schistosomiasis. Both antigens are recognized by individuals naturally resistant to Schistosoma mansoni infection and induced protective immunity in the murine model. Three Sm14 epitopes and eleven paramyosin epitopes were selected by their ability to bind to different HLA-DR molecules using the TEPITOPE computer program, and these peptides were synthetically produced. The cellular recognition of Sm14 and paramyosin epitopes by peripheral blood mononuclear cells of individuals living in endemic area for schistosomiasis was tested by T cell proliferation assay. Among all Sm14 and paramyosin epitopes studied, Sm14-3 was preferentially recognized by individuals naturally resistant to S. mansoni infection while Para-5 was preferentially recognized by individuals resistant to reinfection. These two peptides represent promising antigens to be used in an experimental vaccine against schistosomiasis, since their preferential recognition by resistant individuals suggest their involvement in the induction of protective immunity.

Immunogenicity and Vaccine Potential of Dipeptidic Multiple Antigen Peptides from Schistosoma mansoni Glyceraldehyde 3-Phosphate Dehydrogenase

Six peptides, A, B1, B, C, D and E, derived from the primary sequence of Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase (SG3PDH) were selected based on lowest homology to human glyceraldehyde 3-P dehydrogenase (G3PDH), multimerized in dipeptidic multiple antigen peptide (D-MAP) constructs and used for the immunization of BALB/c mice. Tetrabranched D-MAPs A-B, B1-C and D-E and the bis-D-MAP B-E elicited strong cell-mediated and antibody responses against immunogen, unit peptides and their cognate sequences in the native and denatured protein. D-MAP A-B induced protection against challenge infection. Immunization with D-MAP B1-C failed to affect the challenge worm parameters, probably because peptides B1 and C, previously shown to elicit immune responses associated with increase and decrease in challenge worm fertility, respectively, induced immune responses with opposing effects when combined in a D-MAP construct. A similar suggestion may explain the failure of D-MAP D-E to protect the host against challenge infection. In contrast, immunization with D-MAP B-E resulted in robust protection of the host, possibly because it contains peptides known to evoke immune responses associated with a significant decrease in challenge worm burden and fertility. The data together suggest that the specificity, not the quantity, of the induced immune responses is the determining factor for the efficacy of synthetic peptide-based vaccine for schistosomiasis.

Vaccination with antioxidant enzymes confers protective immunity against challenge infection with Schistosoma mansoni

Schistosoma mansoni, an intravascular parasite, lives in a hostile environment in close contact with host humoral and cellular cytotoxic factors. To establish itself in the host, the parasite has evolved a number of immune evasion mechanisms, such as antioxidant enzymes. Our laboratory has demonstrated that the expression of antioxidant enzymes is developmentally regulated, with the highest levels present in the adult worm, the stage least susceptible to immune elimination, and the lowest levels in the larval stages, the most susceptible to immune elimination. Vaccination of mice with naked DNA constructs containing Cu/Zn cytosolic superoxide dismutase (CT-SOD), signal-peptide containing SOD or glutathione peroxidase (GPX) showed significant levels of protection compared to a control group. We have further shown that vaccination with SmCT-SOD but not SmGPX results in elimination of adult worms. Anti-oxidant enzyme vaccine candidates offer an advance over existing vaccine strategies that all seem to target the larval developmental stages in that they target adult worms and thus may have therapeutic as well as prophylactic value. To eliminate the potential for cross-reactivity of SmCT-SOD with human superoxide dismutase, we identified parasite-specific epitope-containing peptides. Our results serve as a basis for developing a subunit vaccine against schistosomiasis.

Cross-reactivity of Schistosoma mansoni cytosolic superoxide dismutase, a protective vaccine candidate, with host superoxide dismutase and identification of parasite-specific B epitopes

Schistosoma mansoni, an intravascular parasite, has evolved a number of immune evasion mechanisms to establish itself in the host, such as antioxidant enzymes. Our laboratory has demonstrated that the highest levels of certain antioxidant enzymes are found in adult worms, which are the least susceptible to immune killing. Vaccination of mice with naked DNA constructs containing the gene encoding Cu/Zn cytosolic superoxide dismutase (SmCT-SOD) showed significant levels of protection compared to a control group, and our data demonstrate that the adult worms are a target of the immune response that confers resistance in SmCT-SOD DNA-vaccinated mice. Because SmCT-SOD shows significant identity with the human homologue, we evaluated the reactivity of anti-SmCT-SOD antibodies derived from SmCT-SOD-immunized mice and rabbits and from S. mansoni-infected individuals to human superoxide dismutase (hSOD) and SmCT-SOD parasite-specific peptides to assess the potential for autoimmune responses from immunization with the recombinant molecule. In addition, we evaluated the ability of various SmCT-SOD adjuvant-delivered immunizations to induce cross-reactive antibodies. Both mouse and rabbit antibodies generated against SmCT-SOD recognized the denatured form of hSOD. The same antibodies did not recognize nondenatured hSOD. Sera from infected individuals with different clinical forms of schistosomiasis recognized SmCT-SOD but not hSOD. Antibodies from mice immunized with different SmCT-SOD-containing formulations of both DNA and protein were able to recognize SmCT-SOD-derived peptides but not soluble hSOD. All together, these findings serve as a basis for developing a subunit vaccine against schistosomiasis.