Can antibody conjugated nanomicelles alter the prospect of antibody targeted therapy against schistosomiasis mansoni?

BACKGROUND

CLA (conjugated linoleic acid)-mediated activation of the schistosome tegument-associated sphingomyelinase and consequent disruption of the outer membrane might allow host antibodies to access the apical membrane antigens. Here, we investigated a novel approach to enhance specific antibody delivery to concealed surface membrane antigens of Schistosoma mansoni utilising antibody-conjugated-CLA nanomicelle technology.

METHODOLOGY/PRINCIPAL FINDINGS

We invented and characterised an amphiphilic CLA-loaded whey protein co-polymer (CLA-W) as an IV injectable protein nanocarrier. Rabbit anti-Schistosoma mansoni infection (anti-SmI) and anti-Schistosoma mansoni alkaline phosphatase specific IgG antibodies were purified from rabbit sera and conjugated to the surface of CLA-W co-polymer to form antibody-conjugated-CLA-W nanomicelles (Ab-CLA-W). We investigated the schistosomicidal effects of CLA-W and Ab-CLA-W in a mouse model of Schistosoma mansoni against early and late stages of infection. Results showed that conjugation of nanomicelles with antibodies, namely anti-SmI, significantly enhanced the micelles' schistosomicidal and anti-pathology activities at both the schistosomula and adult worm stages of the infection resulting in 64.6%-89.9% reductions in worm number; 72.5-94% and 66.4-85.2% reductions in hepatic eggs and granulomas, respectively. Treatment induced overall improvement in liver histopathology, reducing granuloma size and fibrosis and significantly affecting egg viability. Indirect immunofluorescence confirmed CLA-W-mediated antigen exposure on the worm surface. Electron microscopy revealed extensive ultrastructural damage in worm tegument induced by anti-SmI-CLA-W.

CONCLUSION/SIGNIFICANCE

The novel antibody-targeted nano-sized CLA delivery system offers great promise for treatment of Schistosoma mansoni infection and control of its transmission. Our in vivo observations confirm an immune-mediated enhanced effect of the schistosomicidal action of CLA and hints at the prospect of nanotechnology-based immunotherapy, not only for schistosomiasis, but also for other parasitic infections in which chemotherapy has been shown to be immune-dependent. The results propose that the immunodominant reactivity of the anti-SmI serum, Schistosoma mansoni fructose biphosphate aldolase, SmFBPA, merits serious attention as a therapeutic and vaccine candidate.

Metabolomics reveal alterations in arachidonic acid metabolism in Schistosoma mekongi after exposure to praziquantel

BACKGROUND

Mekong schistosomiasis is a parasitic disease caused by the blood-dwelling fluke Schistosoma mekongi. This disease contributes to human morbidity and mortality in the Mekong region, posing a public health threat to people in the area. Currently, praziquantel (PZQ) is the drug of choice for the treatment of Mekong schistosomiasis. However, the molecular mechanisms of PZQ action remain unclear, and Schistosoma PZQ resistance has been reported occasionally. Through this research, we aimed to use a metabolomic approach to identify the potentially altered metabolic pathways in S. mekongi associated with PZQ treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Adult stage S. mekongi were treated with 0, 20, 40, or 100 μg/mL PZQ in vitro. After an hour of exposure to PZQ, schistosome metabolites were extracted and studied with mass spectrometry. The metabolomic data for the treatment groups were analyzed with the XCMS online platform and compared with data for the no treatment group. After low, medium (IC50), and high doses of PZQ, we found changes in 1,007 metabolites, of which phosphatidylserine and anandamide were the major differential metabolites by multivariate and pairwise analysis. In the pathway analysis, arachidonic acid metabolism was found to be altered following PZQ treatment, indicating that this pathway may be affected by the drug and potentially considered as a novel target for anti-schistosomiasis drug development.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that arachidonic acid metabolism is a possible target in the parasiticidal effects of PZQ against S. mekongi. Identifying potential targets of the effective drug PZQ provides an interesting viewpoint for the discovery and development of new agents that could enhance the prevention and treatment of schistosomiasis.

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.

Schistosoma mansoni glyceraldehyde-3-phosphate dehydrogenase enhances formation of the blood-clot lysis protein plasmin

Schistosomes are intravascular blood flukes that cause the parasitic disease schistosomiasis. In agreement with Schistosoma mansoni (Sm) proteomic analysis, we show here that the normally intracellular glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is also found at the parasite surface; live worms from all intravascular life stages display GAPDH activity. Suppressing GAPDH gene expression using RNA interference significantly lowers this live worm surface activity. Medium in which the worms are cultured overnight displays essentially no activity, showing that the enzyme is not shed or excreted but remains associated with the worm surface. Immunolocalization experiments confirm that the enzyme is highly expressed in the parasite tegument (skin). Surface activity in schistosomula amounts to ∼8% of that displayed by equivalent parasite lysates. To address the functional role of SmGAPDH, we purified the protein following its expression in Escherichiacoli strain DS113. The recombinant protein displays optimal enzymatic activity at pH 9.2, shows robust activity at the temperature of the parasite's hosts, and has a Michaelis-Menten constant for glyceraldehyde-3-phosphate (GAP) of 1.4 mM±0.24. We show that recombinant SmGAPDH binds plasminogen (PLMG) and promotes PLMG conversion to its active form (plasmin) in a dose response in the presence of tissue plasminogen activator. Since plasmin is a key mediator of thrombolysis, our results support the hypothesis that SmGAPDH, a host-interactive tegumental protein that can enhance PLMG activation, could help degrade blood clots around the worms in the vascular microenvironment and thus promote parasite survival in vivoThis article has an associated First Person interview with the first author of the paper.

Immunofluorescent Localization of Proteins in Schistosoma mansoni

Immunofluorescence allows the detection, visualization, and localization of proteins by using the ability of antibodies to firmly bind to specific antigens. Proteins must be accessible to thorough interaction with the specific antibodies. Different immune evasion mechanisms of parasites are directed to hamper or prevent access of antibodies to critical proteins or virulence factors. The blood fluke Schistosoma mansoni would not survive a day in the host blood capillaries if antibodies were able to readily bind to proteins located at the surface and mediate its attrition and demise by the complement system and/or the FcγR- or FcαR-bearing leukocytes. The worm surface is the area of parasite-host interaction and the route to critical nutrients, but is selectively permeable, allowing access of nutrient molecules but not host antibodies. Gentle procedures, which, however, are not commonly in use in vivo, are required to increase the permeability of the parasite outer membrane shield to just allow access of specific antibodies and identify and localize the proteins at the apical surface. Robust methods involving acetone, methanol, and Triton X-100 treatment lead to disintegration of the dual lipid bilayer cover with exposure of the proteins located in the tegument beneath. Internal proteins may not be accessed except following cryostat or paraffin sectioning. Accordingly, vaccine-induced specific antibodies to the apical surface or tegument proteins are unable to harm intact parasites. Specific antibodies to surface membrane proteins may only add to the action of administered or endo schistosomicides via acceleration of killing and interference with repair of severely and lightly impacted parasites, respectively. Therefore, careful immunofluorescent localization of S. mansoni proteins is important for devising the different control strategies against infection.

Phosphoproteomics analysis of male and female Schistosoma mekongi adult worms

Schistosoma mekongi is one of the major causative agents of human schistosomiasis in Southeast Asia. Praziquantel is now the only drug available for treatment and there are serious concerns about parasite resistance to it. Therefore, a dataset of schistosome targets is necessary for drug development. Phosphorylation regulates signalling pathways to control cellular processes that are important for the parasite's growth and reproduction. Inhibition of key phosphoproteins may reduce the severity of schistosomiasis. In this research, we studied the phosphoproteomes of S. mekongi male and female adult worms by using computational and experimental approaches. Using a phosphoproteomics approach, we determined that 88 and 44 phosphoproteins were male- and female-biased, respectively. Immunohistochemistry using anti-phosphoserine antibodies demonstrated phosphorylation on the tegument and muscle of male S. mekongi worms and on the vitelline gland and gastrointestinal tract of female worms. This research revealed S. mekongi sex-dependent phosphoproteins. Our findings provide a better understanding of the role of phosphorylation in S. mekongi and could be integrated with information from other Schistosoma species to facilitate drug and vaccine development.

Protective immune responses against Schistosoma mansoni infection by immunization with functionally active gut-derived cysteine peptidases alone and in combination with glyceraldehyde 3-phosphate dehydrogenase

BACKGROUND

Schistosomiasis, a severe disease caused by parasites of the genus Schistosoma, is prevalent in 74 countries, affecting more than 250 million people, particularly children. We have previously shown that the Schistosoma mansoni gut-derived cysteine peptidase, cathepsin B1 (SmCB1), administered without adjuvant, elicits protection (>60%) against challenge infection of S. mansoni or S. haematobium in outbred, CD-1 mice. Here we compare the immunogenicity and protective potential of another gut-derived cysteine peptidase, S. mansoni cathepsin L3 (SmCL3), alone, and in combination with SmCB1. We also examined whether protective responses could be boosted by including a third non-peptidase schistosome secreted molecule, glyceraldehyde 3-phosphate dehydrogenase (SG3PDH), with the two peptidases.

METHODOLOGY/PRINCIPAL FINDINGS

While adjuvant-free SmCB1 and SmCL3 induced type 2 polarized responses in CD-1 outbred mice those elicited by SmCL3 were far weaker than those induced by SmCB1. Nevertheless, both cysteine peptidases evoked highly significant (P < 0.005) reduction in challenge worm burden (54-65%) as well as worm egg counts and viability. A combination of SmCL3 and SmCB1 did not induce significantly stronger immune responses or higher protection than that achieved using each peptidase alone. However, when the two peptidases were combined with SG3PDH the levels of protection against challenge S. mansoni infection reached 70-76% and were accompanied by highly significant (P < 0.005) decreases in worm egg counts and viability. Similarly, high levels of protection were achieved in hamsters immunized with the cysteine peptidase/SG3PDH-based vaccine.

CONCLUSIONS/SIGNIFICANCE

Gut-derived cysteine peptidases are highly protective against schistosome challenge infection when administered subcutaneously without adjuvant to outbred CD-1 mice and hamsters, and can also act to enhance the efficacy of other schistosome antigens, such as SG3PDH. This cysteine peptidase-based vaccine should now be advanced to experiments in non-human primates and, if shown promise, progressed to Phase 1 safety trials in humans.

Biochemical and biophysical methodologies open the road for effective schistosomiasis therapy and vaccination

BACKGROUND

Schistosomiasis caused by blood-dwelling flukes, namely Schistosoma mansoni and Schistosoma haematobium is a severe debilitating disease, widespread in sub-Saharan Africa, the Middle East, and South America. Developing and adult worms are unscathed by the surrounding immune effectors and antibodies because the parasite is protected by a double lipid bilayer armor which allows access of nutrients, while binding of specific antibodies is denied.

SCOPE OF REVIEW

Fluorescence recovery after bleaching, extraction of surface membrane cholesterol by methyl-β-cyclodextrin, inhibition and activation of sphingomyelin biosynthesis and hydrolysis, and elastic incoherent and quasi-elastic neutron scattering approaches have helped to clarify the basic mechanism of this immune evasion, and showed that sphingomyelin (SM) molecules in the worm apical lipid bilayer form with surrounding water molecules a tight hydrogen bond barrier. Viability of the parasite and permeability of the outer shield are controlled by equilibrium between SM biosynthesis and activity of a tegument-associated neutral sphingomyelinase (nSMase).

MAJOR CONCLUSIONS

Excessive nSMase activation by polyunsaturated fatty acids (PUFA), such as arachidonic acid (ARA) leads to disruption of the SM molecules and associated hydrogen bond network, with subsequent access of host antibodies and immune effectors to the outer membrane and eventual parasite death.

GENERAL SIGNIFICANCE

ARA was predicted and shown to be a potent schistosomicide in vitro and in vivo in experimental animals and in children. Additionally, it was advocated that schistosomiasis vaccine candidates should be selected uniquely among excretory-secretory products of developing worms, as contrary to cytosolic and surface membrane antigens, they are able to activate the effector functions of the host antibodies and toxic molecules. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo".

Schistosomiasis in Egypt: A never-ending story?

Schistosomiasis has plagued the Egyptian population since the antiquity. The disease is still a public health problem in Egypt, despite the tendency of being overlooked. In the first part of this review, the past and current trends of schistosomiasis in Egypt are reviewed, including history, epidemiology, morbidity, therapy, and control of the disease. Most of these aspects are more or less relevant to other schistosome-endemic regions all over the world. As only one drug is currently available for individual treatment and preventive mass chemotherapy, the quest for complementary measures is urgently warranted. Indeed, one promising approach is the discovery of a vaccine. Herein, we point out the efforts of the Egyptian scientists to develop an efficacious and affordable vaccine against schistosomiasis - a step forward in the battle of elimination of Schistosoma infection. Based on the candidate vaccine antigens, four types of vaccine formulations are discussed: purified antigen vaccines, DNA constructs, attenuated cercariae, and excretory-secretory antigen vaccines. Finally, this review provides insights into this ancient seemingly long-lasting parasitic disease.

Human IgG1 Responses to Surface Localised Schistosoma mansoni Ly6 Family Members Drop following Praziquantel Treatment

Background

The heptalaminate-covered, syncytial tegument is an important anatomical adaptation that enables schistosome parasites to maintain long-term, intravascular residence in definitive hosts. Investigation of the proteins present in this surface layer and the immune responses elicited by them during infection is crucial to our understanding of host/parasite interactions. Recent studies have revealed a number of novel tegumental surface proteins including three (SmCD59a, SmCD59b and Sm29) containing uPAR/Ly6 domains (renamed SmLy6A SmLy6B and SmLy6D in this study). While vaccination with SmLy6A (SmCD59a) and SmLy6D (Sm29) induces protective immunity in experimental models, human immunoglobulin responses to representative SmLy6 family members have yet to be thoroughly explored.

Methodology/Principal Findings

Using a PSI-BLAST-based search, we present a comprehensive reanalysis of the Schistosoma mansoni Ly6 family (SmLy6A-K). Our examination extends the number of members to eleven (including three novel proteins) and provides strong evidence that the previously identified vaccine candidate Sm29 (renamed SmLy6D) is a unique double uPAR/Ly6 domain-containing representative. Presence of canonical cysteine residues, signal peptides and GPI-anchor sites strongly suggest that all SmLy6 proteins are cell surface-bound. To provide evidence that SmLy6 members are immunogenic in human populations, we report IgG₁ (as well as IgG₄ and IgE) responses against two surface-bound representatives (SmLy6A and SmLy6B) within a cohort of S. mansoni-infected Ugandan males before and after praziquantel treatment. While pre-treatment IgG₁ prevalence for SmLy6A and SmLy6B differs amongst the studied population (7.4% and 25.3% of the cohort, respectively), these values are both higher than IgG₁ prevalence (2.7%) for a sub-surface tegumental antigen, SmTAL1. Further, post-treatment IgG₁ levels against surface-associated SmLy6A and SmLy6B significantly drop (p = 0.020 and p < 0.001, respectively) when compared to rising IgG₁ levels against sub-surface SmTAL1.

Conclusions/Significance

Collectively, these results expand the number of SmLy6 proteins found within S. mansoni and specifically demonstrate that surface-associated SmLy6A and SmLy6B elicit immunological responses during infection in endemic communities.

Adult schistosome parasites can live in the human bloodstream for years without being adversely affected by the host immune response. Identifying which proteins are on the surface of the parasite and understanding how they contribute to long-term host/parasite relationships is an essential step in developing novel intervention strategies. Here, utilising a comprehensive bioinformatics approach to identify Schistosoma mansoni gene products sharing distinct surface-associated features including signal peptides, hydrophobic C-termini, disulfide bonds and uPAR/Ly6 domains, we identified eleven proteins of interest. These proteins, reassuringly, include three representatives previously found associated with the schistosome surface (here termed SmLy6A, SmLy6B and SmLy6D) as well as three novel members (SmLy6G, SmLy6H and SmLy6J). To identify if surface-associated SmLy6 members are recognized by S. mansoni infected individuals, we specifically examined antibody responses to SmLy6A and SmLy6B in an endemic human population. Our work expands the number of putative cell surface associated schistosome proteins and provides a greater understanding of the dynamics of antibody responses in endemic communities against two representatives.

Induction of protective immune responses against schistosomiasis using functionally active cysteine peptidases

Each year schistosomiasis afflicts up to 600 million people in 74 tropical and sub-tropical countries, predominantly in the developing world. Yet we depend on a single drug, praziquantel, for its treatment and control. There is no vaccine available but one is urgently needed especially since praziquantel-resistant parasites are likely to emerge at some time in the future. The disease is caused by several worm species of the genus Schistosoma. These express several classes of papain-like cysteine peptidases, cathepsins B and L, in various tissues but particularly in their gastrodermis where they employ them as digestive enzymes. We have shown that sub-cutaneous injection of recombinant and functionally active Schistosoma mansoni cathepsin B1 (SmCB1), or a cathepsin L from a related parasite Fasciola hepatica (FhCL1), elicits highly significant protection (up to 73%) against an experimental challenge worm infection in murine models of schistosomiasis. The immune modulating properties of this subcutaneous injection can boost protection levels (up to 83%) when combined with other S. mansoni vaccine candidates, glyceraldehyde 3-phosphate dehydrogenase (SG3PDH) and peroxiredoxin (PRX-MAP). Here, we discuss these data in the context of the parasite's biology and development, and provide putative mechanism by which the native-like cysteine peptidase induce protective immune responses.

Rigidity and resistance of larval- and adult schistosomes-medium interface

Schistosomiasis is second only to malaria in prevalence and severity, and is still a major health problem in many tropical countries worldwide with about 200-300 million cases and with more than 800 million people at risk of infection. Based on these data, the World Health Organization recommends fostering research efforts for understanding at any level the mechanisms of the infection and then decreasing the social and economical impact of schistosomiasis. A key role is played by the parasite apical lipid membrane, which is entirely impervious to the surrounding elements of the immune system. We have previously demonstrated that the interaction between schistosomes and surrounding medium is governed by a parasite surface membrane sphingomyelin-based hydrogen barrier. In the present article, the elastic contribution to the total motion as a function of the exchanged wave-vector Q and the mean square displacement values for Schistosoma mansoni larvae and worms and Schistosomahaematobium worms have been evaluated by quasi elastic neutron scattering (QENS). The results point out that S. mansoni larvae show a smaller mean square displacement in comparison to S. mansoni and S. haematobium worms. These values increased by repeating the measurements after one day. These differences, which are analogous to those observed for the diffusion coefficient we previously evaluated, are interpreted in terms of rigidity of the parasite-medium interaction. S. mansoni larvae are the most rigid systems, while S. haematobium worms are the most flexible. In addition, temperature and hypoxia induce a weakening of the schistosome-medium interaction. These evidences are related to the strength of the hydrogen-bonded interaction between parasites and environment that we previously determined. We have shown that S. mansoni worms are characterized by a weakened interaction in respect to the larvae, while the S. haematobium worms more weakly interact with the surrounding medium than S. mansoni. The present QENS analysis allowed us to characterize the rigidity of larval- and adult S. mansoni and S. haematobium-host interface and to relate it to the parasite resistance to the hostile elements of the surrounding medium and to the immune effectors attack.

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.

In vitro and in vivo activities of arachidonic acid against Schistosoma mansoni and Schistosoma haematobium

The development of arachidonic acid (ARA) for treatment of schistosomiasis is an entirely novel approach based on a breakthrough discovery in schistosome biology revealing that activation of parasite tegument-bound neutral sphingomyelinase (nSMase) by unsaturated fatty acids, such as ARA, induces exposure of parasite surface membrane antigens to antibody binding and eventual attrition of developing schistosomula and adult worms. Here, we demonstrate that 5 mM ARA leads to irreversible killing of ex vivo 1-, 3-, 4-, 5-, and 6-week-old Schistosoma mansoni and 9-, 10-, and 12-week-old Schistosoma haematobium worms within 3 to 4 h, depending on the parasite age, even when the worms were maintained in up to 50% fetal calf serum. ARA-mediated worm attrition was prevented by nSMase inhibitors, such as CaCl(2) and GW4869. Scanning and transmission electron microscopy revealed that ARA-mediated worm killing was associated with spine destruction, membrane blebbing, and disorganization of the apical membrane structure. ARA-mediated S. mansoni and S. haematobium worm attrition was reproduced in vivo in a series of 6 independent experiments using BALB/c or C57BL/6 mice, indicating that ARA in a pure form (Sigma) or included in infant formula (Nestle) consistently led to 40 to 80% decrease in the total worm burden. Arachidonic acid is already marketed for human use in the United States and Canada for proper development of newborns and muscle growth of athletes; thus, ARA has potential as a safe and cost-effective addition to antischistosomal therapy.

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.