Associations between specific antibody responses and resistance to reinfection in a Senegalese population recently exposed to Schistosoma mansoni

IgG persistence showed weak clinical aspects in chronic schistosomiasis patients

Schistosomiasis is a chronic parasitic disease, which affects the quality of daily life of patients and imposes a huge burden on society. Hepatic fibrosis in response to continuous insult of eggs to the liver is a significant cause of morbidity and mortality. However, the mechanisms of hepatic fibrosis in schistosomiasis are largely undefined. The purpose of our study is to detect the indicator to hepatic fibrosis in schistosomiasis. A total of 488 patients with chronic schistosomiasis japonica were enrolled in our study. The patients were divided into two groups according to liver ultrasound examination, which could indicate liver fibrosis of schistosomiasis with unique reticular changes. Logistic regression analysis showed that globulin, albumin/globulin, GGT levels and anti-Schistosoma IgG were independently associated with liver fibrosis in patients with schistosomiasis and IgG was the largest association of liver fibrosis (OR  2.039, 95% CI 1.293-3.213). We further compared IgG+ patients with IgG- patients. IgG+ patients (ALT 25 U/L, GGT 31 U/L) slightly higher than IgG- patients (ALT 22 U/L, GGT 26 U/L) in ALT and GGT. However, the fibrosis of liver in IgG+ patients (Grade II(19.7%), Grade III(7.3%)) were more severe than that in IgG- patients(Grade II(12.5%), Grade III(2.9%)) according to the grade of liver ultrasonography. Our results showed anti-Schistosoma IgG was independently associated with liver fibrosis in patients with chronic schistosomiasis japonica and patients with persistent anti-Schistosoma IgG might have more liver fibrosis than negative patients despite no obvious clinical signs or symptoms.

Expression of CD117 (c-Kit) on Circulating B Cells in Pediatric Schistosomiasis

Few B cells express CD27, the primary marker for memory B cells, in pediatric schistosomiasis, suggesting B cell malfunction. This study further demonstrates unexpected high expression of CD117 on circulating B cells in children highly exposed to Schistosoma mansoni infectious larvae. CD117 is expressed by immature or lymphoma B cells, but not by mature, circulating cells. We therefore sought to define the significance of CD117 on blood B cells. We found that CD117-positive (CD117⁺) B cells increased with the intensity of schistosome infection. In addition, CD117 expression was reduced on CD23⁺ B cells previously shown to correlate with resistance to infection. Stimulation with a panel of cytokines demonstrated that CD117 levels were upregulated in response to a combination of interleukin 4 (IL-4) and stem cell factor (SCF), the ligand for CD117, whereas IL-2 led to a reduction. In addition, stimulation with SCF generally reduced B cell activation levels. Upon further investigation, it was established that multiple circulating cells expressed increased levels of CD117, including monocytes, neutrophils, and eosinophils, and expression levels correlated with that of B cells. Finally, we identified a population of large circulating cells with features of reticulocytes. Overall, our results suggest that hyperexposure to intravascular parasitic worms elicits immature cells from the bone marrow. Levels of SCF were shown to reduce as children began to transition through puberty. The study results pose an explanation for the inability of children to develop significant immunity to infection until after puberty.

Recent Advances and Methodological Considerations on Vaccine Candidates for Human Schistosomiasis

Schistosomiasis remains a neglected tropical disease of major public health concern with high levels of morbidity in various parts of the world. Although considerable efforts in implementing mass drug administration programs utilizing praziquantel have been deployed, schistosomiasis is still not contained. A vaccine may therefore be an essential part of multifaceted prevention control efforts. In the 1990s, a joint United Nations committee promoting parasite vaccines shortlisted promising candidates including for schistosomiasis discussed below. After examining the complexity of immune responses in human hosts infected with schistosomes, we review and discuss the antigen design and preclinical and clinical development of the four leading vaccine candidates: Sm-TSP-2 in Phase 1b/2b, Sm14 in Phase 2a/2b, Sm-p80 in Phase 1 preparation, and Sh28GST in Phase 3. Our assessment of currently leading vaccine candidates revealed some methodological issues that preclude a fair comparison between candidates and the rationale to advance in clinical development. These include (1) variability in animal models - in particular non-human primate studies - and predictive values of each for protection in humans; (2) lack of consensus on the assessment of parasitological and immunological parameters; (3) absence of reliable surrogate markers of protection; (4) lack of well-designed parasitological and immunological natural history studies in the context of mass drug administration with praziquantel. The controlled human infection model - while promising and unique - requires validation against efficacy outcomes in endemic settings. Further research is also needed on the impact of advanced adjuvants targeting specific parts of the innate immune system that may induce potent, protective and durable immune responses with the ultimate goal of achieving meaningful worm reduction.

Associations of IL13 gene polymorphisms and immune factors with Schistosoma haematobium infection in schoolchildren in four schistosomiasis-endemic communities in Ghana

BACKGROUND

Schistosomiasis remains a major public health issue with over 90% of the prevalence rates recorded in Sub-Saharan Africa. In this study, the relationships between different interleukin gene polymorphisms (IL-13-591A/G, IL-13-1055C/T, IL-13-1258A/G) and Schistosoma haematobium infection levels were evaluated; as well as the host plasma antibodies and cytokine profiles associated with schistosomiasis infection.

METHODOLOGY

A total of 469 school children aged 6 to 19 years from four schistosomiasis-endemic communities in Ghana were involved. Single urine and stool samples were obtained from each pupil, processed via sedimentation and Kato-Katz, and examined via microscopy for Schistosoma and soil-transmitted helminth (STH) eggs. Next, venous blood samples were drawn from 350 healthy pupils, and used to measure antibody and plasma cytokine levels by ELISA. Single nucleotide polymorphisms in the IL-13 gene were genotyped on 71 selected blood samples using the Mass Array technique.

PRINCIPAL FINDINGS AND CONCLUSION

The overall prevalence of urinary schistosomiasis was 21.11%. Community-level prevalences were 17.12%, 32.11%, 20.80%, and 15.32% for Asempaneye, Barikumah, Eyan Akotoguah, and Apewosika respectively. Generally, higher S. haematobium infection prevalence and intensity were recorded for participants with genotypes bearing the IL13-1055C allele, the IL13-591A, and the IL13-1258A alleles. Also, higher S. haematobium infection prevalence was observed among participants in the 12-14-year age group with the IL13-1055C, IL13-591A, and IL13-1258A alleles. Interestingly, higher STH prevalence was also observed among participants with the IL13-1055C, IL13-591A, and IL13-1258A alleles. Furthermore, the age-associated trends of measured antibodies and cytokines of S. haematobium-infected school-children depicted a more pro-inflammatory immune profile for pupils aged up to 1l years, and an increasingly anti-inflammatory profile for pupils aged 12 years and above. This work provides insight into the influence of IL-13 gene polymorphisms on S. haematobium, and STH infections, in school-aged children (SAC).

Comparison of immune responses to Loa loa stage-specific antigen extracts in Loa loa-exposed BALB/c mice upon clearance of infection

Background

Different immune mechanisms are capable of killing developmental stages of filarial nematodes and these mechanisms are also likely to vary between the primary and a challenge infection. However, the lack of a detailed analysis of cytokine, chemokine and immunoglobulin levels in human loiasis is still evident. Therefore, detailed analysis of immune responses induced by the different developmental stages of Loa loa in immune-competent BALB/c mice will aid in the characterization of distinct immune responses that are important for the immunity against loiasis.

Methods

Different developmental stages of L. loa were obtained from human peripheral blood (microfilariae, MF), the transmitting vector, Chrysops (larval stage 3, L3) and infected immune-deficient BALB/cRAG2γc^−/− mice (L4, L5, adult worms). Groups of wildtype BALB/c mice were then injected with the isolated stages and after 42 days post-infection (pi), systemic cytokine, chemokine and immunoglobulin levels were determined. These were then compared to L. loa-specific responses from in vitro re-stimulated splenocytes from individual mice. All parameters were determined using Luminex technology.

Results

In a pilot study, BALB/c mice cleared the different life stages of L. loa within 42 days pi and systemic cytokine, chemokine and immunoglobulin levels were equal between infected and naive mice. Nevertheless, L. loa-specific re-stimulation of splenocytes from mice infected with L5, MF or adult worms led to induction of Th2, Th17 and chemokine secretion patterns.

Conclusions

This study shows that although host immunity remains comparable to naive mice, clearance of L. loa life-cycle development stages can induce immune cell memory leading to cytokine, chemokine and immunoglobulins secretion patterns which might contribute to immunity and protection against reinfection.

Micro Array-Assisted Analysis of Anti-Schistosome Glycan Antibodies Elicited by Protective Vaccination With Irradiated Cercariae

Baboons vaccinated with radiation-attenuated cercariae develop high levels of protection against schistosome infection, correlating to high antibody titres towards schistosome antigens with unknown molecular identity. Using a microarray consisting of glycans isolated from different life-stages of schistosomes, we studied the anti-glycan immunoglobulin (Ig) G and IgM responses in vaccinated and challenged baboons over a time course of 25 weeks. Anti-glycan IgM responses developed early after vaccination, but did not rise in response to later vaccinations. In contrast, anti-glycan IgG developed more slowly, but was boosted by all five subsequent vaccinations. High IgM and IgG levels against O-glycans and glycosphingolipid glycans of cercariae were observed. At the time of challenge, while most antibody levels decreased in the absence of vaccination, IgG towards a subset of glycans containing multiple-fucosylated motifs remained high until 6 weeks post-challenge during challenge parasite elimination, suggesting a possible role of this IgG in protection.

Population level changes in schistosome-specific antibody levels following chemotherapy

AIMS

Previous studies have reported that chemotherapy of schistosomiasis by praziquantel in humans boosts protective antibody responses against S mansoni and S haematobium. A number of studies have reported schistosome-specific antibody levels before and after chemotherapy. Using these reports, a meta-analysis was conducted to identify predictors of population level change in schistosome-specific antibody levels after chemotherapy.

METHODS AND RESULTS

Following a systematic review, 92 observations from 26 articles published between 1988 and 2013 were included in this study. Observations were grouped by antigen type and antibody isotypes for the classification and regression tree (CART) analysis. The study showed that the change in antibody levels was variable: (a) between different human populations and (b) according to the parasite antigen and antibody isotypes. Thus, while anti-worm responses predominantly increased after chemotherapy, anti-egg responses decreased or did not show a significant trend. The change in antibody levels depended on a combination of age and infection intensity for anti-egg IgA, IgM, IgG1, IgG2 and anti-worm IgM and IgG.

CONCLUSION

The study results are consistent with praziquantel treatment boosting anti-worm antibody responses. However, there is considerable heterogeneity in post-treatment changes in specific antibody levels that is related to host age and pre-treatment infection intensity.

Antibody responses to Schistosoma mansoni schistosomula antigens

While antigens from Schistosoma schistosomula have been suggested as potential vaccine candidates, the association between antibody responses with schistosomula antigens and infection intensity at reinfection is not well known. Schistosoma mansoni-infected individuals were recruited from a schistosomiasis endemic area in Uganda (n = 372), treated with 40 mg/kg praziquantel (PZQ) and followed up at five weeks and at one year post-treatment. Pre-treatment and five weeks post-treatment immunoglobulin (Ig) E, IgG1 and IgG4 levels against recombinant schistosomula antigens rSmKK7, rSmLy6A, rSmLy6B and rSmTSP7 were measured using ELISA. Factors associated with detectable pre-treatment or post-treatment antibody response against the schistosomula antigens and the association between five-week antibody responses and one year post-treatment reinfection intensity among antibody responders were examined. Being male was associated with higher pre-treatment IgG1 to rSmKK7, rSmLy6a and AWA. Five weeks post-treatment antibody responses against schistosomula antigens were not associated with one year post-treatment reinfection intensity among antibody responders' antibody levels against rSmKK7, rSmLy6B and rSmTSP7 dropped, but increased against rSmLy6A, AWA and SEA at five weeks post-treatment among antibody responders. S. mansoni-infected individuals exhibit detectable antibody responses to schistosomula antigens that are affected by treatment. These findings indicate that schistosomula antigens induce highly varied antibody responses and could have implications for vaccine development.

Glycan Microarray-Assisted Identification of IgG Subclass Targets in Schistosomiasis

Infection with schistosomes is accompanied by the induction of antibodies against the parasite. Despite having IgG against both protein and glycan antigens, infected individuals remain chronically infected until treated, and re-infection is common in endemic areas as immunity does not develop effectively. Parasite specific IgG subclasses may differ in functionality and effectivity with respect to effector functions that contribute to parasite killing and immunity. In this study, we investigated if specific IgG subclasses target specific antigenic schistosome glycan motifs during human infection. Sera from 41 S. mansoni infected individuals from an endemic area in Uganda were incubated on two glycan microarrays, one consisting of a large repertoire of schistosome glycoprotein- and glycolipid- derived glycans and the other consisting of chemically synthesized core xylosylated and fucosylated N-glycans also expressed by schistosomes. Our results show that highly antigenic glycan motifs, such as multi-fucosylated terminal GalNAc(β1-4)GlcNAc (LDN) can be recognized by all IgG subclasses of infection sera, however with highly variable intensities. Detailed examination of core-modified N-glycan targets revealed individual antibody responses specific for core-xylosylated and core α3-fucosylated glycan motifs that are life stage specifically expressed by schistosomes. IgG1 and IgG3 were detected against a range of N-glycan core structures, but IgG2 and IgG4, when present, were specific for the core α3-fucose and xylose motifs that were previously found to be IgE targets in schistosomiasis, and in allergies. This study is the first to address IgG subclass responses to defined helminth glycans.

Functional Studies of T Regulatory Lymphocytes in Human Schistosomiasis in Western Kenya

Immunoregulation is considered a common feature of Schistosoma mansoni infections, and elevated levels of T regulatory (Treg) lymphocytes have been reported during chronic human schistosomiasis. We now report that the removal of Treg (CD4+/CD25^hi/CD127^low lymphocytes) from peripheral blood mononuclear cells (PBMCs) of S. mansoni–infected individuals leads to increased levels of phytohemagglutinin (PHA)-stimulated interferon gamma (IFNγ) production and decreased interleukin-10 (IL-10) responses. Exposure to schistosome antigens did not result in measurable IFNγ by either PBMC or Treg-depleted populations. Interleukin-10 responses to soluble egg antigens (SEA) by PBMC were unchanged by Treg depletion, but the depletion of Treg greatly decreased IL-10 production to soluble worm antigenic preparation (SWAP). Proliferative responses to PHA increased upon Treg removal, but responses to SEA or SWAP did not, unless only initially low responders were evaluated. Addition of anti-IL-10 increased PBMC proliferative responses to either SEA or SWAP, but did not alter responses by Treg-depleted cells. Blockade by anti-transforming growth factor-beta (TGF-β) increased SEA but not SWAP proliferative responses by PBMC, whereas anti-TGF-β increased both SEA- and SWAP-stimulated responses by Treg-depleted cultures. Addition of both anti-IL-10 and anti-TGF-β to PBMC or Treg-depleted populations increased proliferation of both populations to either SEA or SWAP. These studies demonstrate that Treg appear to produce much of the antigen-stimulated IL-10, but other cell types or subsets of Treg may produce much of the TGF-β. The elevated levels of Treg seen in chronic schistosomiasis appear functional and involve IL-10 and TGF-β in antigen-specific immunoregulation perhaps leading to regulation of immunopathology and/or possibly decreased immunoprotective responses.

DEWORMING DELUSIONS? MASS DRUG ADMINISTRATION IN EAST AFRICAN SCHOOLS

Recent debates about deworming school-aged children in East Africa have been described as the 'Worm Wars'. The stakes are high. Deworming has become one of the top priorities in the fight against infectious diseases. Staff at the World Health Organization, the Gates Foundation and the World Bank (among other institutions) have endorsed the approach, and school-based treatments are a key component of large-scale mass drug administration programmes. Drawing on field research in Uganda and Tanzania, and engaging with both biological and social evidence, this article shows that assertions about the effects of school-based deworming are over-optimistic. The results of a much-cited study on deworming Kenyan school children, which has been used to promote the intervention, are flawed, and a systematic review of randomized controlled trials demonstrates that deworming is unlikely to improve overall public health. Also, confusions arise by applying the term deworming to a variety of very different helminth infections and to different treatment regimes, while local-level research in schools reveals that drug coverage usually falls below target levels. In most places where data exist, infection levels remain disappointingly high. Without indefinite free deworming, any declines in endemicity are likely to be reversed. Moreover, there are social problems arising from mass drug administration that have generally been ignored. Notably, there are serious ethical and practical issues arising from the widespread practice of giving tablets to children without actively consulting parents. There is no doubt that curative therapy for children infected with debilitating parasitic infections is appropriate, but overly positive evaluations of indiscriminate deworming are counter-productive.

Single-sex infection with female Schistosoma mansoni cercariae mitigates hepatic fibrosis after secondary infection

BACKGROUND

Infection with Schistosoma spp. affects more than 258 million people worldwide. Current treatment strategies are mainly based on the anthelmintic Praziquantel, which is effective against adult worms but neither prevents re-infection nor cures severe liver damage. The best long-term strategy to control schistosomiasis may be to develop an immunization. Therefore, we designed a two-step Schistosoma mansoni infection model to study the immune-stimulating effect of a primary infection with either male or female cercariae, measured on the basis of TH1/TH2-response, granuloma size and hepatic fibrosis after a secondary bisexual S. mansoni challenge.

METHODOLOGY/PRINCIPLE FINDINGS

As a first step, mice were infected with exclusively female, exclusively male, or a mixture of male and female S. mansoni cercariae. 11 weeks later they were secondarily infected with male and female S. mansoni cercariae. At week 19, infection burden, granuloma size, collagen deposition, serum cytokine profiles and the expression of inflammatory genes were analyzed. Mice initially infected with female S. mansoni cercariae displayed smaller hepatic granulomas, livers and spleens, less hepatic fibrosis and higher expression of Ctla4. In contrast, a prior infection with male or male and female S. mansoni did not mitigate disease progression after a bisexual challenge.

CONCLUSIONS/SIGNIFICANCE

Our findings provide evidence that an immunization against S. mansoni is achievable by exploiting gender-specific differences between schistosomes.

Biosensor for Hepatocellular Injury Corresponds to Experimental Scoring of Hepatosplenic Schistosomiasis in Mice

Severe hepatosplenic injury of mansonian schistosomiasis is caused by Th2 mediated granulomatous response against parasite eggs entrapped within the periportal tissue. Subsequent fibrotic scarring and deformation/sclerosing of intrahepatic portal veins lead to portal hypertension, ascites, and oesophageal varices. The murine model of Schistosoma mansoni (S. mansoni) infection is suitable to establish the severe hepatosplenic injury of disease within a reasonable time scale for the development of novel antifibrotic or anti-infective strategies against S. mansoni infection. The drawback of the murine model is that the material prepared for complex analysis of egg burden, granuloma size, hepatic inflammation, and fibrosis is limited due to small amounts of liver tissue and blood samples. The objective of our study was the implementation of a macroscopic scoring system for mice livers to determine infection-related organ alterations of S. mansoni infection. In addition, an in vitro biosensor system based on the detection of hepatocellular injury in HepG2/C3A cells following incubation with serum of moderately (50 S. mansoni cercariae) and heavily (100 S. mansoni cercariae) infected mice affirmed the value of our scoring system. Therefore, our score represents a valuable tool in experimental schistosomiasis to assess severity of hepatosplenic schistosomiasis and reduce animal numbers by saving precious tissue samples.

Modeling the long-term persistence of hepatitis A antibody after a two-dose vaccination schedule in Argentinean children

BACKGROUND

Long-term seroprotection data are essential for decision-making on the need and timing of vaccine boosters. Based on data from longitudinal serological studies, modeling can provide estimates on long-term antibody persistence and inform such decision-making.

METHODS

We examined long-term anti-hepatitis A virus (anti-HAV) antibody persistence in Argentinean children ≤15 years after the initial study where they completed a 2-dose course of inactivated hepatitis A vaccine (Avaxim 80U Pediatric, Sanofi Pasteur, Lyon, France). Blood serum samples were taken at baseline, 2 weeks (post first dose), 6 months (pre-booster), 6.5 months (post-booster), 10 years and 14-15 years after first vaccine dose. We fitted 8 statistical model types, predominantly mixed effects models, to anti-HAV persistence data, to identify the most appropriate and best fitting models for our data set and to predict individuals' anti-HAV levels and seroprotection rates up to 30 years post vaccination.

RESULTS

Fifty-four children (mean age at enrollment 30.4 months) were enrolled up to 15 years post first vaccine dose. There were 3 distinct periods of antibody concentration: rapid rise up to peak concentration post-booster, rapid decay from post-booster to 10 years, followed by slower decay. A 3-segmented linear mixed effects model was the most appropriate for the data set. Extrapolating based on the available 14-15-year follow-up, the analysis predicted that 88% of individuals anti-HAV seronegative prior to vaccination would remain seroprotected at 30 years post vaccination and lifelong seroprotection for vaccinees seropositive prior to vaccination.

CONCLUSIONS

Currently available data demonstrate that Avaxim 80U Pediatric confers to most vaccinees a high level of seroprotection against hepatitis A infection for at least 20-30 years.

Development of a Schistosoma mansoni shotgun O-glycan microarray and application to the discovery of new antigenic schistosome glycan motifs

Upon infection with Schistosoma, antibody responses are mounted that are largely directed against glycans. Over the last few years significant progress has been made in characterising the antigenic properties of N-glycans of Schistosoma mansoni. Despite also being abundantly expressed by schistosomes, much less is understood about O-glycans and antibody responses to these have not yet been systematically analysed. Antibody binding to schistosome glycans can be analysed efficiently and quantitatively using glycan microarrays, but O-glycan array construction and exploration is lagging behind because no universal O-glycanase is available, and release of O-glycans has been dependent on chemical methods. Recently, a modified hydrazinolysis method has been developed that allows the release of O-glycans with free reducing termini and limited degradation, and we applied this method to obtain O-glycans from different S. mansoni life stages. Two-dimensional HPLC separation of 2-aminobenzoic acid-labelled O-glycans generated 362 O-glycan-containing fractions that were printed on an epoxide-modified glass slide, thereby generating the first shotgun O-glycan microarray containing naturally occurring schistosome O-glycans. Monoclonal antibodies and mass spectrometry showed that the O-glycan microarray contains well-known antigenic glycan motifs as well as numerous other, potentially novel, antibody targets. Incubations of the microarrays with sera from Schistosoma-infected humans showed substantial antibody responses to O-glycans in addition to those observed to the previously investigated N- and glycosphingolipid glycans. This underlines the importance of the inclusion of these often schistosome-specific O-glycans in glycan antigen studies and indicates that O-glycans contain novel antigenic motifs that have potential for use in diagnostic methods and studies aiming at the discovery of vaccine targets.

Immunology of human schistosomiasis

There is a wealth of immunologic studies that have been carried out in experimental and human schistosomiasis that can be classified into three main areas: immunopathogenesis, resistance to reinfection and diagnostics. It is clear that the bulk of, if not all, morbidity due to human schistosomiasis results from immune-response-based inflammation against eggs lodged in the body, either as regulated chronic inflammation or resulting in fibrotic lesions. However, the exact nature of these responses, the antigens to which they are mounted and the mechanisms of the critical regulatory responses are still being sorted out. It is also becoming apparent that protective immunity against schistosomula as they develop into adult worms develops slowly and is hastened by the dying of adult worms, either naturally or when they are killed by praziquantel. However, as with anti-egg responses, the responsible immune mechanisms and inducing antigens are not clearly established, nor are any potential regulatory responses known. Finally, a wide variety of immune markers, both cellular and humoral, can be used to demonstrate exposure to schistosomes, and immunologic measurement of schistosome antigens can be used to detect, and thus diagnose, active infections. All three areas contribute to the public health response to human schistosome infections.

Characteristics of IL-17 induction by Schistosoma japonicum infection in C57BL/6 mouse liver

Schistosomiasis japonica is a severe tropical disease caused by the parasitic worm Schistosoma japonicum. Among the most serious pathological effects of S. japonicum infection are hepatic lesions (cirrhosis and fibrosis) and portal hypertension. Interleukin-17 (IL-17) is a pro-inflammatory cytokine involved in the pathogenesis of many inflammatory and infectious conditions, including schistosomiasis. We infected C57BL/6 mice with S. japonicum and isolated lymphocytes from the liver to identify cell subsets with high IL-17 expression and release using flow cytometry and ELISA. Expression and release of IL-17 was significantly higher in hepatic lymphocytes from infected mice compared with control mice in response to both non-specific stimulation with anti-CD3 monoclonal antibody plus/anti-CD28 monoclonal antibody and PMA plus ionomycin. We then compared IL-17 expression in three hepatic T-cell subsets, T helper, natural killer T and γδT cells, to determine the major source of IL-17 during infection. Interleukin-17 was induced in all three subsets by PMA + ionomycin, but γδT lymphocytes exhibited the largest increase in expression. We then established a mouse model to further investigate the role of IL-17 in granulomatous and fibrosing inflammation against parasite eggs. Reducing IL-17 activity using anti-IL-17A antibodies decreased infiltration of inflammatory cells and collagen deposition in the livers of infected C57BL/6 mice. The serum levels of soluble egg antigen (IL)-specific IgGs were enhanced by anti-IL-17A monoclonal antibody blockade, suggesting that IL-17 normally serves to suppress this humoral response. These findings suggest that γδT cells are the most IL-17-producing cells and that IL-17 contributes to granulomatous inflammatory and fibrosing reactions in S. japonicum-infected C57BL/6 mouse liver.

Comparative efficacy of one versus two doses of praziquantel on cure rate of Schistosoma mansoni infection and re-infection in Mayuge District, Uganda

BACKGROUND

The current recommended control strategy for schistosomiasis is annual treatment using 40 mg/kg of praziquantel. However, praziquantel is only effective on adult worms and giving a second dose may increase its efficacy. We assessed the effect of one versus two doses of praziquantel on cure rate and re-infection with Schistosoma mansoni in a high endemic community along Lake Victoria, Uganda.

METHODOLOGY

To investigate the effect of the two regimens, 395 infected people were randomised into two groups; one received a single standard dose of praziquantel (Distocide® 600 mg, Shin Poong Pharmaceuticals, Seoul, Republic of Korea), 40mg/kg body weight, while the other group received a second dose 2 weeks later. Cure rate and infection intensity were assessed 9 weeks after the first treatment using standard parasitological procedures. Re-infection levels were monitored 8 and 24 months after treatment.

RESULTS

Those who received two doses were more likely to be cured (69.7%) compared to those who received a single dose (47.9%) (χ(2) = 18.5, p < 0.001). Geometric mean intensity (GMI) of infection at 9 weeks (eggs per gram of faeces [epg]) was 12.0 epg (CI95: 8.9-16.1) for individuals who received 2 doses and 22.1 epg (CI95: 16.9-28.8) for those in the single dose arm. Eight months after treatment, prevalence of re-infection for individuals in the double dose arm (61.6%, CI95: 50.2-73.1) was not significantly different from that of those in a single dose arm (68.3%, CI95: 59.9-76.8). The difference in GMI of re-infection for individuals in the single dose arm (33.8 epg, CI95: 23.2-49.3) and those in the double dose arm (34.5 epg, CI95: 24.7-48.1) was not significant. Twenty four months after treatment, prevalence of re-infection was not significantly different. The difference in GMI of re-infection for those in the single dose arm (57.5 epg, CI95: 33.9-97.5) and those in the double dose arm (42.2 epg, CI95: 29.9-59.6) was also insignificant.

CONCLUSION

Our results suggest that a second dose of praziquantel given 2 weeks after the first dose improves cure rate and reduces S. mansoni infection intensity. However, there is no added advantage on reduction of S. mansoni re-infection by administering two doses of praziquantel. CLINICAL TRIALS.GOV IDENTIFIER: NCT00215267.

Rapidly boosted Plasma IL-5 induced by treatment of human Schistosomiasis haematobium is dependent on antigen dose, IgE and eosinophils

Background

IgE specific to worm antigen (SWA) and pre-treatment eosinophil number, are associated with human immunity to re-infection with schistosomes after chemotherapeutic treatment. Treatment significantly elevates circulating IL-5 24-hr post-treatment of Schistosoma mansoni. Here we investigate if praziquantel treatment of human schistosomiasis haematobium also boosts circulating IL-5, the immunological and parasitological factors that predispose to this, and the relationship between these and subsequent immunity to post-treatment re-infection.

Methodology/Principle Findings

The relationship between pre-treatment SWA-IgE, eosinophil number and infection intensity and the 24-hr post-treatment IL-5 boost was investigated in a Malian cohort (aged 5–40 yrs), exposed to S. haematobium. Eotaxin levels were measured at 24-hr post-treatment as a proxy of eosinophil migration. The relationship between the 24-hr post-treatment IL-5 boost and later eosinophil numbers and SWA-IgE levels (9-wk post-treatment) was examined, then investigated in the context of subsequent levels of re-infection (2-yr post-treatment). Circulating IL-5 levels increased 24-hr post-treatment and were associated with pre-treatment infection intensity, SWA-IgE levels, eosinophil number, as well as 24-hr post-treatment eotaxin levels. 24-hr IL-5 levels were, in turn, significantly associated with eosinophil number and elevated SWA-IgE 9-wk later. These SWA-IgE levels were significantly associated with immunity to re-infection.

Conclusions/Significance

Early IL-5 production after treatment-induced exposure to S. haematobium worm antigen is positively associated with antigen dose (infection intensity), IgE availability for arming of effector cells at time of treatment and subsequent eosinophil migration response (as indicated by eotaxin levels). The IL-5 produced is positively associated with increased downstream eosinophil number and increases in specific IgE levels, implicating this cytokine boost and its down-stream consequences in the production and maintenance of IgE, and subsequent re-infection immunity.

Partial human immunity to infection with trematode worms of the genus Schistosoma is associated with IgE specific to adult worm-derived antigens and eosinophils. Treatment studies of Schistosoma infection allow us to examine the temporal features of the immune response post-antigen exposure, their inter-dependence and their relationship with re-infection levels. Here the boosted levels of the cytokine IL-5, measured at 24-hrs post-treatment of a Malian cohort, aged 5–40 yrs, were found to be significantly associated with pre-treatment levels of IgE to worm-derived antigens and eosinophil number, linking this rapid response to two of the main correlates of human immunity to these parasites. The IL-5 levels at 24-hr were in turn related to increased eosinophil counts and SWA-IgE levels at 9-wks post-treatment. In line with previous studies SWA-IgE was associated with resistance to re-infection. The study therefore identifies temporal relationships between immune mediators prior to and post treatment induced antigen exposure that are associated with resistance to re-infection.

Alterations in peripheral blood B cell subsets and dynamics of B cell responses during human schistosomiasis

Antibody responses are thought to play an important role in control of Schistosoma infections, yet little is known about the phenotype and function of B cells in human schistosomiasis. We set out to characterize B cell subsets and B cell responses to B cell receptor and Toll-like receptor 9 stimulation in Gabonese schoolchildren with Schistosoma haematobium infection. Frequencies of memory B cell (MBC) subsets were increased, whereas naive B cell frequencies were reduced in the schistosome-infected group. At the functional level, isolated B cells from schistosome-infected children showed higher expression of the activation marker CD23 upon stimulation, but lower proliferation and TNF-α production. Importantly, 6-months after 3 rounds of praziquantel treatment, frequencies of naive B cells were increased, MBC frequencies were decreased and with the exception of TNF-α production, B cell responsiveness was restored to what was seen in uninfected children. These data show that S. haematobium infection leads to significant changes in the B cell compartment, both at the phenotypic and functional level.

Schistosomiasis affects over 200 million people and especially children in developing countries. It causes general hyporesponsiveness of the immune system, which until now has predominantly been described for various T cell subsets as well as dendritic cells. B cells in this context have not yet been investigated. To address this question, we phenotyped B cell subsets present in peripheral blood from S. haematobium infected and uninfected schoolchildren living in an endemic area in Lambaréné, Gabon. Children with schistosomiasis had an increased frequency of various memory B cell subsets, including subsets associated with B cell exhaustion, and a concomitant decrease in naive B cells. To study the effect of Schistosoma infection on B cells in more detail we isolated peripheral blood B cells and found that B cells from infected children had a reduced capacity to proliferate and produce TNF-α in response to both B cell receptor and Toll-like receptor stimulation. These results provide new insights into the role of B cells in the host immune response to schistosomiasis and may provide a novel target for therapeutic strategies.

Schistosomiasis in areas of low endemicity: a new era in diagnosis

Parasitological detection of Schistosoma is the cornerstone of schistosomiasis diagnosis in areas of transmission worldwide. However, a steep decrease of sensitivity in low-endemicity areas (LEAs) compromises estimation of schistosomiasis. Despite the restricted utilization of molecular and immunodiagnostic techniques, recent improvements and advances have been contributing to change this scenario, especially in LEAs. Nonetheless, the main issue in a new era of diagnosis overcomes technical advances per se and relates to the loss of 'gold standards' in schistosomiasis diagnosis in LEAs. Here, we review and discuss the current role of molecular and immunodiagnostic methods in schistosomiasis management.

Differential anti-glycan antibody responses in Schistosoma mansoni-infected children and adults studied by shotgun glycan microarray

BACKGROUND

Schistosomiasis (bilharzia) is a chronic and potentially deadly parasitic disease that affects millions of people in (sub)tropical areas. An important partial immunity to Schistosoma infections does develop in disease endemic areas, but this takes many years of exposure and maturation of the immune system. Therefore, children are far more susceptible to re-infection after treatment than older children and adults. This age-dependent immunity or susceptibility to re-infection has been shown to be associated with specific antibody and T cell responses. Many antibodies generated during Schistosoma infection are directed against the numerous glycans expressed by Schistosoma. The nature of glycan epitopes recognized by antibodies in natural schistosomiasis infection serum is largely unknown.

METHODOLOGY/PRINCIPAL FINDINGS

The binding of serum antibodies to glycans can be analyzed efficiently and quantitatively using glycan microarray approaches. Very small amounts of a large number of glycans are presented on a solid surface allowing binding properties of various glycan binding proteins to be tested. We have generated a so-called shotgun glycan microarray containing natural N-glycan and lipid-glycan fractions derived from 4 different life stages of S. mansoni and applied this array to the analysis of IgG and IgM antibodies in sera from children and adults living in an endemic area. This resulted in the identification of differential glycan recognition profiles characteristic for the two different age groups, possibly reflecting differences in age or differences in length of exposure or infection.

CONCLUSIONS/SIGNIFICANCE

Using the shotgun glycan microarray approach to study antibody response profiles against schistosome-derived glycan elements, we have defined groups of infected individuals as well as glycan element clusters to which antibody responses are directed in S. mansoni infections. These findings are significant for further exploration of Schistosoma glycan antigens in relation to immunity.

Review: analysis of parasite and other skewed counts

OBJECTIVE

To review methods for the statistical analysis of parasite and other skewed count data.

METHODS

Statistical methods for skewed count data are described and compared, with reference to a 10-year period of Tropical Medicine and International Health (TMIH). Two parasitological datasets are used for illustration.

RESULTS

The review of TMIH found 90 articles, of which 89 used descriptive methods and 60 used inferential analysis. A lack of clarity is noted in identifying the measures of location, in particular the Williams and geometric means. The different measures are compared, emphasising the legitimacy of the arithmetic mean for the skewed data. In the published articles, the t test and related methods were often used on untransformed data, which is likely to be invalid. Several approaches to inferential analysis are described, emphasising (1) non-parametric methods, while noting that they are not simply comparisons of medians, and (2) generalised linear modelling, in particular with the negative binomial distribution. Additional methods, such as the bootstrap, with potential for greater use are described.

CONCLUSIONS

Clarity is recommended when describing transformations and measures of location. It is suggested that non-parametric methods and generalised linear models are likely to be sufficient for most analyses.

Schistosoma haematobium infection levels determine the effect of praziquantel treatment on anti-schistosome and anti-mite antibodies

Field studies show an association between schistosome infection and atopy, but the effects of anti-helminthic treatment on this association have not yet been investigated in human populations with different schistosome endemicity levels. This study aimed to compare the effects of anti-helminthic treatment on responses directed against the house dust mite Dermatophagoides pteronyssinus (Derp1) and Schistosoma haematobium in Zimbabwean populations living in high and low schistosome infection areas. Derp1- and schistosome-specific IgE and IgG4 antibodies were quantified by ELISA before and 6 weeks after anti-helminthic treatment. Following treatment, there were changes in the immune responses, which varied with place of residence. After allowing for the effects of sex, age and baseline infection intensity, there was no significant treatment effect on the change in anti-schistosome IgE and IgG4 in the high infection area. However, the anti-schistosome IgE/IgG4 ratio increased significantly, while anti-Derp1 IgE responses decreased as a result of treatment. In the low infection area, treatment resulted in a significant increase in anti-worm IgE levels, but there was no significant treatment effect on anti-schistosome or anti-Derp1 IgE/IgG4 ratios. Thus, the study shows that the level of schistosome endemicity affects the host responses to schistosome and mite antigens following anti-helminthic treatment.

Parasite glycans and antibody-mediated immune responses in Schistosoma infection

Schistosome infections in humans are characterized by the development of chronic disease and high re-infection rates after treatment due to the slow development of immunity. It appears that anti-schistosome antibodies are at least partially mediating protective mechanisms. Efforts to develop a vaccine based on immunization with surface-exposed or secreted larval or worm proteins are ongoing. Schistosomes also express a large number of glycans as part of their glycoprotein and glycolipid repertoire, and antibody responses to those glycans are mounted by the infected host. This observation raises the question if glycans might also form novel vaccine targets for immune intervention in schistosomiasis. This review summarizes current knowledge of antibody responses and immunity in experimental and natural infections with Schistosoma, the expression profiles of schistosome glycans (the glycome), and antibody responses to individual antigenic glycan motifs. Future directions to study anti-glycan responses in schistosomiasis in more detail in order to address more precisely the possible role of glycans in antibody-mediated immunity are discussed.

Sm-p80-based DNA vaccine provides baboons with levels of protection against Schistosoma mansoni infection comparable to those achieved by the irradiated cercarial vaccine

To date, no vaccine is available to prevent human schistosomiasis. We have targeted a protein of Schistosoma mansoni that plays an important role in the surface membrane renewal process, a mechanism widely believed to be utilized by the parasite as an immune evasion strategy. Sm-p80 antigen is a promising vaccine target because of its documented immunogenicity, protective efficacy, and antifecundity effects observed in both experimental murine and nonhuman primate models of this infectious disease. In the present study, we report that, in a vector approved for human use (VR1020), an Sm-p80-based DNA vaccine formulation confers a 46% reduction in the worm burden in a baboon (Papio anubis) model. Baboons vaccinated with Sm-p80-VR1020 had a 28% decrease in egg production after challenge with the infectious parasite. Sm-p80-VR1020 vaccine elicited robust immune responses to specific antigen Sm-p80, including immunoglobulin (Ig) G, its subtypes IgG1 and IgG2, and IgA and IgM in vaccinated animals. When stimulated in vitro with recombinant Sm-p80, peripheral blood mononuclear cells and splenocytes from baboons vaccinated with Sm-p80-VR1020 produced considerably higher levels of T helper 1 response-enhancing cytokines (interleukin [IL]-2 and interferon-gamma) than T helper 2 (Th2) response-enhancing cytokines (IL-4 and IL-10). Peripheral blood mononuclear cells produced a significantly higher number of spot-forming units for interferon-gamma than for IL-4 in enzyme-linked immunosorbent spot assays. A mixed T helper 1/T helper 2 type of humoral and T cell responses was generated after immunization with Sm-p80-VR1020. These findings again highlight the potential of Sm-p80 as a promising vaccine candidate for schistosomiasis.

Influence of exposure history on the immunology and development of resistance to human Schistosomiasis mansoni

Background

Previous studies suggest that humans can acquire immunity to reinfection with schistosomes, most probably due to immunologic mechanisms acquired after exposure to dying schistosome worms.

Methodology/Principal Findings

We followed longitudinally two cohorts of adult males occupationally exposed to Schistosoma mansoni by washing cars (120 men) or harvesting sand (53 men) in Lake Victoria. Men were treated with praziquantel each time S. mansoni infection was detected. In car washers, a significant increase in resistance to reinfection, as measured by the number of cars washed between cure and reinfection, was observed after the car washers had experienced, on average, seven cures. In the car washers who developed resistance, the level of schistosome-specific IgE increased between baseline and the time at which development of resistance was first evidenced. In the sand harvesters, a significant increase in resistance, as measured by the number of days worked in the lake between cure and reinfection, was observed after only two cures. History of exposure to S. mansoni differed between the two cohorts, with the majority of sand harvesters being lifelong residents of a village endemic for S. mansoni and the majority of car washers having little exposure to the lake before they began washing cars. Immune responses at study entry were indicative of more recent infections in car washers and more chronic infections in sand harvesters.

Conclusions/Significance

Resistance to reinfection with S. mansoni can be acquired or augmented by adults after multiple rounds of reinfection and cure, but the rate at which resistance is acquired by this means depends on immunologic status and history of exposure to S. mansoni infection.

Schistosomiasis is a parasitic blood fluke infection of 200 million people worldwide. We have shown that humans can acquire immunity to reinfection after repeated exposures and cures with the drug praziquantel. The increase in resistance to reinfection was associated with an increase in schistosome-specific IgE. The ability to develop resistance and the rate at which resistance was acquired varied greatly in two cohorts of men within close geographic proximity and with similar occupational exposures to schistosomes. These differences are likely attributable to differences in history of exposure to Schistosoma mansoni infection and immunologic status at baseline, with those acquiring immunity faster having lifelong S. mansoni exposure and immunologic evidence of chronic S. mansoni infection. As many conflicting results have been reported in the literature regarding immunologic parameters associated with the development of resistance to schistosome infection, exposure history and prior immune status should be considered in the design of future immuno-epidemiologic studies.

Schistosoma mansoni infection in a rural area of the Jequitinhonha Valley, Minas Gerais, Brazil: analysis of exposure risk

This study examines the relative contribution of age-specific total IgE levels, eosinophils and water contact behavior to the prevalence and intensity (geometric mean egg counts) of Schistosoma mansoni infection in the poor rural population of Virgem das Graças in northern Minas Gerais State. In bivariate analysis, age was strongly correlated with both prevalence and intensity of infection, while eosinophil levels with prevalence only (p<0.0001); IgE levels and 5 demographic and socioeconomic variables were moderately correlated with prevalence (p<0.05), as were number of persons per room and TBM (total body minutes) with egg counts. In multivariate analysis, after controlling for demographic and socioeconomic factors, only total IgE levels were significantly correlated with both prevalence (p=0.248, 95% CI=1.01-1.11) and intensity (p=0.0217, 95% CI=0.01-0.14) of infection and eosinophil levels with prevalence (p=0.0005, 95% CI=1.07-1.24). Although any causal relationship cannot be confirmed by a cross-sectional study, we demonstrated an associated decrease in prevalence and intensity of S. mansoni infection with increased IgE levels.

Effect of praziquantel treatment of Schistosoma mansoni during pregnancy on intensity of infection and antibody responses to schistosome antigens: results of a randomised, placebo-controlled trial

Background

Praziquantel treatment of schistosomiasis during pregnancy was only recommended in 2002; hence the effects of treatment during pregnancy are not fully known. We have therefore evaluated the effects on infection intensity and the immunological effects of praziquantel treatment against Schistosoma mansoni during pregnancy, compared with treatment after delivery.

Methods

A nested cohort of 387 Schistosoma mansoni infected women was recruited within a larger trial of de-worming during pregnancy. Women were randomised to receive praziquantel or placebo during pregnancy. All women were treated after delivery. Infection intensity after treatment was assessed by a single Kato-Katz examination of stool samples with duplicate slides and categorised as undetected, light (1–99 eggs per gram (epg)), moderate (100–399 epg) or heavy (≥400 epg). Antibodies against S. mansoni worm and egg antigens were measured by ELISA. Results were compared between women first treated during pregnancy and women first treated after delivery.

Results

At enrolment, 252 (65.1%) of the women had light infection (median (IQR) epg: 35 (11, 59)), 75 (19.3%) moderate (median (IQR) epg: 179(131, 227)) and 60 (15.5%) had heavy infection (median (IQR) epg: 749 (521, 1169)) with S. mansoni. At six weeks after praziquantel treatment during pregnancy S. mansoni infection was not detectable in 81.9% of the women and prevalence and intensity had decreased to 11.8% light, 4.7% moderate and 1.6% heavy a similar reduction when compared with those first treated after delivery (undetected (88.5%), light (10.6%), moderate (0.9%) and heavy (0%), p = 0.16). Parasite specific antibody levels were lower during pregnancy than after delivery. Praziquantel treatment during pregnancy boosted anti-worm IgG isotypes and to a lesser extent IgE, but these boosts were less pronounced than in women whose treatment was delayed until after delivery. Praziquantel had limited effects on antibodies against egg antigens.

Conclusion

S mansoni antigen-specific antibody levels and praziquantel-induced boosts in antibody levels were broadly suppressed during pregnancy, but this was not associated with major reduction in the efficacy of praziquantel. Long-term implications of these findings in relation to resistance to re-infection remain to be explored.

Trial registration

International Standard Randomised Controlled Trial Number for the current study: ISRCTN32849447 http://www.controlled-trials.com/ISRCTN32849447/elliott

Protective and antifecundity effects of Sm-p80-based DNA vaccine formulation against Schistosoma mansoni in a nonhuman primate model

Schistosomiasis is an important parasitic disease for which there is no available vaccine. We have focused on a functionally important antigen of Schistosoma mansoni, Sm-p80, as a vaccine candidate because of its consistent immunogenicity, protective potential and antifecundity effect observed in murine models; and for its pivotal role in the immune evasion process. In the present study we report that an Sm-p80-based DNA vaccine formulation confers 38% reduction in worm burden in a nonhuman primate model, the baboon (Papio anubis). Animals immunized with Sm-p80-pcDNA3 exhibited a decrease in egg production by 32%. Sm-p80 DNA elicited specific immune responses that include IgG; its subtypes IgG1 and IgG2; and IgM in vaccinated animals. Peripheral blood mononuclear cells (PBMCs) from immunized animals when stimulated in vitro with Sm-p80 produced appreciably more Th1 response enhancing cytokines (IL-2, IFN-gamma) than Th2 response enhancing cytokines (IL-4, IL-10). PBMCs produced appreciably more spot-forming units for INF-gamma than for IL-4 in enzyme-linked immunosorbent spot (ELISPOT) assays. Overall it appears that even though a mixed (Th1/Th2) type of humoral antibody response was generated following immunization with Sm-p80; the dominant protective immune response is Th1 type. These data reinforce the potential of Sm-p80 as an excellent vaccine candidate for schistosomiasis.

Neurological complications of Schistosoma infection

Schistosomiasis is a parasitic disease caused by blood flukes of the genus Schistosoma. Currently more than 200 million people worldwide are affected. Neuroschistosomiasis constitutes a severe presentation of the disease. Neurological symptoms result from the inflammatory response of the host to egg deposition in the brain and spinal cord. Neurological complications of cerebral schistosomiasis include delirium, loss of consciousness, seizures, dysphasia, visual field impairment, focal motor deficits and ataxia. Cerebral and cerebellar tumour-like neuroschistosomiasis can present with increased intracranial pressure, headache, nausea and vomiting, and seizures. Myelopathy (acute transverse myelitis and subacute myeloradiculopathy) is the most common neurological complication of Schistosoma mansoni infection. Schistosomal myelopathy tends to occur early after infection and is more likely to be symptomatic than cerebral schistosomiasis. The conus medullaris and cauda equina are the most common sites of involvement. Severe schistosomal myelopathy can provoke a complete flaccid paraplegia with areflexia, sphincter dysfunction and sensory disturbances. Schistosomicidal drugs, steroids and surgery are the currently available treatments for neuroschistosomiasis. Rehabilitation and multidisciplinary team care are needed in severely disabled patients.