Age-related antibody profiles in Schistosoma haematobium infections in a rural community in Zimbabwe

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).

Immune Evasion Strategies of Schistosomes

Human schistosomes combat the unique immune systems of two vastly different hosts during their indirect life cycles. In gastropod molluscs, they face a potent innate immune response composed of variable immune recognition molecules and highly phagocytic hemocytes. In humans, a wide variety of innate and adaptive immune processes exist in proximity to these parasites throughout their lifespan. To survive and thrive as the second most common parasitic disease in humans, schistosomes have evolved many techniques to avoid and combat these targeted host responses. Among these techniques are molecular mimicry of host antigens, the utilization of an immune resistant outer tegument, the secretion of several potent proteases, and targeted release of specific immunomodulatory factors affecting immune cell functions. This review seeks to describe these key immune evasion mechanisms, among others, which schistosomes use to survive in both of their hosts. After diving into foundational observational studies of the processes mediating the establishment of schistosome infections, more recent transcriptomic and proteomic studies revealing crucial components of the host/parasite molecular interface are discussed. In order to combat this debilitating and lethal disease, a comprehensive understanding of schistosome immune evasion strategies is necessary for the development of novel therapeutics and treatment plans, necessitating the discussion of the numerous ways in which these parasitic flatworms overcome the immune responses of both hosts.

Six rounds of annual praziquantel treatment during a national helminth control program significantly reduced schistosome infection and morbidity levels in a cohort of schoolchildren in Zimbabwe

BACKGROUND

The World Health Organization recommends that schistosomiasis be treated through Mass Drug Administration (MDA). In line with this recommendation, Zimbabwe commenced a national helminth control program in 2012 targeting schoolchildren throughout the country for 6 years. This study, part of a larger investigation of the impact of helminth treatment on the overall health of the children, determined the effect of annual praziquantel treatment on schistosome infection and morbidity in a cohort of children during Zimbabwe's 6-year national helminth control program.

METHODOLOGY/PRINCIPAL FINDINGS

A school-based longitudinal study was carried out in 35 sentinel sites across Zimbabwe from September 2012 to November 2017. The sentinel sites were selected following a countrywide survey conducted in 280 primary schools. Schistosoma haematobium was diagnosed using the urine filtration technique. Schistosoma mansoni was diagnosed using both the Kato-Katz and formol-ether concentration techniques. S. haematobium morbidity was determined through detection of macro and microhaematuria. A cohort of children aged 6-15 years old was surveyed annually before MDA and 6 weeks post treatment. Maximum treatment coverage reached 90% over the 6 rounds of MDA. At baseline S. haematobium infection prevalence and intensity were 31.7% (95% CI = 31.1-32.2) and 28.75 eggs/10ml urine (SEM = 0.81) respectively, while S. mansoni prevalence and intensity were 4.6% (95% CI = 4.4-4.8) and 0.28 eggs/25mg (SEM = 0.02). Prior to the 6th round of MDA, S. haematobium infection prevalence had reduced to 1.56% (p<0.001) and infection intensity to 0.07 (SEM 0.02). Six weeks later after the 6th MDA, both were 0. Similarly the prevalence of S. haematobium morbidity as indicated by haematuria also fell significantly from 32.3% (95% CI = 29.9-34.6) to 0% (p< 0.0001) prior to the final MDA. For S.mansoni, both prevalence and intensity had decreased to 0 prior to the 6th MDA. After 6 rounds of annual MDA, prevalence and intensity of both schistosome species decreased significantly to 0% (p< 0.0001).

CONCLUSION

Zimbabwe's helminth control program significantly reduced schistosome infection intensity and prevalence and urogenital schistosomiasis morbidity prevalence in a cohort of school-aged children, moving the schistosome prevalence in the children from moderate to low by WHO classification. These findings will inform the design of the country's next stage interventions for helminth control and eventual elimination.

High resistance of water buffalo against reinfection with Schistosoma japonicum

Schistosomiasis is a zoonotic parasitic disease threatening tens of millions people and farm animals. Water buffalos are a major reservoir for schistosomiasis and a control target. Epidemiological surveys suggest that buffalos can develop resistance against Schistosoma japonicum reinfection. In the present paper, relative to control animals, we report an over 97% worm burden reduction after two rounds of infection with S. japonicum and treatment with Praziquantel (PZQ). Relative to control animals, shorter length of female worms, and lower egg counts (over 87.7% reduction rates) were observed in reinfected buffalos. We also found that the reinfected buffalos had significantly higher levels of IL-4, IL-10, and IFN-γ, 4-9 weeks after the secondary infection, and a significantly higher level of specific IgG antibodies before infection. Our results confirmed that after infection buffalos develop resistance against S. japonicum reinfection, and that this resistance is mainly due to acquired immunity. These findings may aid in the future vaccine design for water buffalos.

Host immunity, nutrition and coinfection alter longitudinal infection patterns of schistosomes in a free ranging African buffalo population

Schistosomes are trematode parasites of global importance, causing infections in millions of people, livestock, and wildlife. Most studies on schistosomiasis, involve human subjects; as such, there is a paucity of longitudinal studies investigating parasite dynamics in the absence of intervention. As a consequence, despite decades of research on schistosomiasis, our understanding of its ecology in natural host populations is centered around how environmental exposure and acquired immunity influence acquisition of parasites, while very little is known about the influence of host physiology, coinfection and clearance in the absence of drug treatment. We used a 4-year study in free-ranging African buffalo to investigate natural schistosome dynamics. We asked (i) what are the spatial and temporal patterns of schistosome infections; (ii) how do parasite burdens vary over time within individual hosts; and (iii) what host factors (immunological, physiological, co-infection) and environmental factors (season, location) explain patterns of schistosome acquisition and loss in buffalo? Schistosome infections were common among buffalo. Microgeographic structure explained some variation in parasite burdens among hosts, indicating transmission hotspots. Overall, parasite burdens ratcheted up over time; however, gains in schistosome abundance in the dry season were partially offset by losses in the wet season, with some hosts demonstrating complete clearance of infection. Variation among buffalo in schistosome loss was associated with immunologic and nutritional factors, as well as co-infection by the gastrointestinal helminth Cooperia fuelleborni. Our results demonstrate that schistosome infections are surprisingly dynamic in a free-living mammalian host population, and point to a role for host factors in driving variation in parasite clearance, but not parasite acquisition which is driven by seasonal changes and spatial habitat utilization. Our study illustrates the power of longitudinal studies for discovering mechanisms underlying parasite dynamics in individual animals and populations.

Group 2 innate lymphoid cell proportions are diminished in young helminth infected children and restored by curative anti-helminthic treatment

BACKGROUND

Group 2 Innate lymphoid cells (ILC2s) are innate cells that produce the TH2 cytokines IL-5 and IL-13. The importance of these cells has recently been demonstrated in experimental models of parasitic diseases but there is a paucity of data on ILC2s in the context of human parasitic infections and in particular of the blood dwelling parasite Schistosoma haematobium.

METHODOLOGY/PRINCIPAL FINDINGS

In this case-control study human peripheral blood ILC2s were analysed in relation to infection with the helminth parasite Schistosoma haematobium. Peripheral blood mononuclear cells of 36 S. haematobium infected and 36 age and sex matched uninfected children were analysed for frequencies of ILC2s identified as Lin-CD45+CD127+CD294+CD161+. ILC2s were significantly lower particularly in infected children aged 6-9 years compared to healthy participants. Curative anti-helminthic treatment resulted in an increase in levels of the activating factor TSLP and restoration of ILC2 levels.

CONCLUSION

This study demonstrates that ILC2s are diminished in young helminth infected children and restored by removal of the parasites by treatment, indicating a previously undescribed association between a human parasitic infection and ILC2s and suggesting a role of ILC2s before the establishment of protective acquired immunity in human schistosomiasis.

Down Regulation of the TCR Complex CD3ζ-Chain on CD3+ T Cells: A Potential Mechanism for Helminth-Mediated Immune Modulation

The CD3ζ forms part of the T cell receptor (TCR) where it plays an important role in coupling antigen recognition to several intracellular signal-transduction pathways leading to T cell effector functions. Down regulation of CD3ζ leads to impairment of immune responses including reduced cell proliferation and cytokine production. In experimental models, helminth parasites have been shown to modulate immune responses directed against them and unrelated antigens, so called bystander antigens, but there is a lack of studies validating these observations in humans. This study investigated the relationship between expression levels of the TCR CD3ζ chain with lymphocyte cell proliferation during human infection with the helminth parasite, Schistosoma haematobium, which causes uro-genital schistosomiasis. Using flow cytometry, peripheral blood mononuclear cells (PBMCs) from individuals naturally exposed to S. haematobium in rural Zimbabwe were phenotyped, and expression levels of CD3ζ on T cells were related to intensity of infection. In this population, parasite infection intensity was inversely related to CD3ζ expression levels (p < 0.05), consistent with downregulation of CD3ζ expression during helminth infection. Furthermore, PBMC proliferation was positively related to expression levels of CD3ζ (p < 0.05) after allowing for confounding variables (host age, sex, and infection level). CD3ζ expression levels had a differing relationship between immune correlates of susceptibility and immunity, measured by antibody responses, indicating a complex relationship between immune activation status and immunity. The relationships between the CD3ζ chain of the TCR and schistosome infection, PBMC proliferation and schistosome-specific antibody responses have not previously been reported, and these results may indicate a mechanism for the impaired T cell proliferative responses observed during human schistosome infection.

Comparing parasitological vs serological determination of Schistosoma haematobium infection prevalence in preschool and primary school-aged children: implications for control programmes

To combat schistosomiasis, the World Health Organization (WHO) recommends that infection levels are determined prior to designing and implementing control programmes, as the treatment regimens depend on the population infection prevalence. However, the sensitivity of the parasitological infection diagnostic method is less reliable when infection levels are low. The aim of this study was to compare levels of Schistosoma haematobium infection obtained by the parasitological method vs serological technique. Infection levels in preschool and primary school-aged children and their implications for control programmes were also investigated. Infection prevalence based on serology was significantly higher compared with that based on parasitology for both age groups. The difference between infection levels obtained using the two methods increased with age. Consequentially, in line with the WHO guidelines, the serological method suggested a more frequent treatment regimen for this population compared with that implied by the parasitological method. These findings highlighted the presence of infection in children aged ⩽5 years, further reiterating the need for their inclusion in control programmes. Furthermore, this study demonstrated the importance of using sensitive diagnostic methods as this has implications on the required intervention controls for the population.

Genital schistosomiasis and its unacknowledged role on HIV transmission in the STD intervention studies

Treatment of sexually transmitted infections (STIs) has been hypothesised to decrease HIV transmission. Although observational studies show an association between STIs and HIV, only one prospective randomised controlled trial (RCT) has confirmed this. Female genital schistosomiasis can cause genital lesions, accompanied by bloody discharge, ulcers or malodorous discharge. Genital schistosomiasis is common, starts before puberty and symptoms can be mistaken for STIs. Three observational studies have found an association between schistosomiasis and HIV. Genital lesions that develop in childhood are chronic. This paper sought to explore the possible effects of schistosomiasis on the RCTs of STI treatment for HIV prevention.

In the study sites, schistosomiasis was a likely cause of genital lesions. The studies recruited women that may have had genital schistosomal lesions established in childhood. Schistosomiasis endemic areas with different prevalence levels may have influenced HIV incidence in intervention and control sites differently, and some control group interventions may have influenced the impact of schistosomiasis on the study results. Schistosomiasis is a neglected cause of genital tract disease. It may have been an independent cause of HIV incidence in the RCTs of STI treatment for HIV prevention and may have obscured the findings of these trials.

Puberty and Age-related Changes in Susceptibility to Schistosome Infection

Recent data from outbreaks of schistosomiasis in immunologically naive populations have refuelled the debate concerning the nature or existence of protective, acquired immunity to schistosomiasis in humans. Data from endemic communities provide some compelling evidence for an abrupt change in reinfection rates that coincides with puberty. We suggest that the hormonal changes of adrenarche may hold the key to understanding the relative resistance to infection found in adults.

Age-related patterns in human myeloid dendritic cell populations in people exposed to Schistosoma haematobium infection

BACKGROUND

Urogenital schistosomiasis is caused by the helminth parasite Schistosoma haematobium. In high transmission areas, children acquire schistosome infection early in life with infection levels peaking in early childhood and subsequently declining in late childhood. This age-related infection profile is thought to result from the gradual development of protective acquired immunity. Age-related differences in schistosome-specific humoral and cellular responses have been reported from several field studies. However there has not yet been a systematic study of the age-related changes in human dendritic cells, the drivers of T cell polarisation.

METHODS

Peripheral blood mononuclear cells were obtained from a cohort of 61 Zimbabwean aged 5-45 years with a S. haematobium prevalence of 47.5%. Two subsets of dendritic cells, myeloid and plasmacytoid dendritic cells (mDCs and pDCs), were analyzed by flow cytometry.

FINDINGS

In this population, schistosome infection levels peaked in the youngest age group (5-9 years), and declined in late childhood and adulthood (10+ years). The proportions of both mDCs and pDCs varied with age. However, for mDCs the age profile depended on host infection status. In the youngest age group infected people had enhanced proportions of mDCs as well as lower levels of HLA-DR on mDCs than un-infected people. In the older age groups (10-13 and 14-45 years) infected people had lower proportions of mDCs compared to un-infected individuals, but no infection status-related differences were observed in their levels of HLA-DR. Moreover mDC proportions correlated with levels of schistosome-specific IgG, which can be associated with protective immunity. In contrast proportions of pDCs varied with host age, but not with infection status.

CONCLUSIONS

Our results show that dendritic cell proportions and activation in a human population living in schistosome-endemic areas vary with host age reflecting differences in cumulative history of exposure to schistosome infection.

Immunoproteomics Identification of Major IgE and IgG4 Reactive Schistosoma japonicum Adult Worm Antigens Using Chronically Infected Human Plasma

Immunoepidemiological studies from endemic areas have revealed age-dependent resistance correlation with increased level of IgE and decreased level of IgG4 antibodies in responses to schistosomes' soluble worm antigen. However, there have been limited studies on analyses of major antigens that provoke IgE and IgG4 immune response during chronic stage of schistosomiasis. In this study, for the first time, immunoproteomics approach has been applied to identify S. japonicum worm antigens in liquid fractions that are recognized by IgE and IgG4 antibody using plasma from chronically infected population. ProteomeLabPF 2D fractionated 1-D and 2-D fractions of SWA antigens were screened using pooled high IgE/IgG4 reactive plasma samples by dot-blot technique. In 1-D fractions, IgE isotype was detected by fewer antigenic fractions (43.2%). The most recognized isotype was IgG3 (79.5%) followed by IgG1 (75.0%) and IgG4 (61.4%). Liquid chromatography MS/MS protein sequencing of reactive 2-D fractions revealed 18 proteins that were identified, characterized and gene ontology categories determined. 2-D fractions containing proteins such as zinc finger, RanBP2-type, domain-containing protein were strongly recognized by IgE and moderately by IgG4 whereas fractions containing proteins such as ubiquitin-conjugating enzyme and cytosolic II 5'-nucleotidase strongly recognizing by IgG subclasses (IgG1, IgG3 and IgG4) but not IgE. By this study, a simple and reproducible proteomic method has been established to identify major immunoreactive S. japonicum antigens. It is anticipated that this will stimulate further research on the immunogenicity and protective potential of proteins identified as well as discovery of novel compounds that have therapeutic importance.

Protective immunity to Schistosoma haematobium infection is primarily an anti-fecundity response stimulated by the death of adult worms

Protective immunity against human schistosome infection develops slowly, for reasons that are not yet fully understood. For many decades, researchers have attempted to infer properties of the immune response from epidemiological studies, with mathematical models frequently being used to bridge the gap between immunological theory and population-level data on schistosome infection and immune responses. Here, building upon earlier model findings, stochastic individual-based models were used to identify model structures consistent with observed field patterns of Schistosoma haematobium infection and antibody responses, including their distributions in cross-sectional surveys, and the observed treatment-induced antibody switch. We found that the observed patterns of infection and antibody were most consistent with models in which a long-lived protective antibody response is stimulated by the death of adult S. haematobium worms and reduces worm fecundity. These findings are discussed with regard to current understanding of human immune responses to schistosome infection.

Explaining observed infection and antibody age-profiles in populations with urogenital schistosomiasis

Urogenital schistosomiasis is a tropical disease infecting more than 100 million people in sub-Saharan Africa. Individuals in endemic areas endure repeated infections with long-lived schistosome worms, and also encounter larval and egg stages of the life cycle. Protective immunity against infection develops slowly with age. Distinctive age-related patterns of infection and specific antibody responses are seen in endemic areas, including an infection 'peak shift' and a switch in the antibody types produced. Deterministic models describing changing levels of infection and antibody with age in homogeneously exposed populations were developed to identify the key mechanisms underlying the antibody switch, and to test two theories for the slow development of protective immunity: that (i) exposure to dying (long-lived) worms, or (ii) experience of a threshold level of antigen, is necessary to stimulate protective antibody. Different model structures were explored, including alternative stages of the life cycle as the main antigenic source and the principal target of protective antibody, different worm survival distributions, antigen thresholds and immune cross-regulation. Models were identified which could reproduce patterns of infection and antibody consistent with field data. Models with dying worms as the main source of protective antigen could reproduce all of these patterns, but so could some models with other continually-encountered life stages acting as the principal antigen source. An antigen threshold enhanced the ability of the model to replicate these patterns, but was not essential for it to do so. Models including either non-exponential worm survival or cross-regulation were more likely to be able to reproduce field patterns, but neither of these was absolutely required. The combination of life cycle stage stimulating, and targeted by, antibody was found to be critical in determining whether models could successfully reproduce patterns in the data, and a number of combinations were excluded as being inconsistent with field data.

Exposure, infection, systemic cytokine levels and antibody responses in young children concurrently exposed to schistosomiasis and malaria

Despite the overlapping distribution of Schistosoma haematobium and Plasmodium falciparum infections, few studies have investigated early immune responses to both parasites in young children resident in areas co-endemic for the parasites. This study measures infection levels of both parasites and relates them to exposure and immune responses in young children. Levels of IgM, IgE, IgG4 directed against schistosome cercariae, egg and adult worm and IgM, IgG directed against P. falciparum schizonts and the merozoite surface proteins 1 and 2 together with the cytokines IFN-γ, IL-4, IL-5, IL-10 and TNF-α were measured by ELISA in 95 Zimbabwean children aged 1–5 years. Schistosome infection prevalence was 14·7% and that of Plasmodium infection was 0% in the children. 43. 4% of the children showed immunological evidence of exposure to schistosome parasites and 13% showed immunological evidence of exposure to Plasmodium parasites. Schistosome–specific responses, indicative of exposure to parasite antigens, were positively associated with cercariae-specific IgE responses, while Plasmodium-specific responses, indicative of exposure to parasite antigens, were negatively associated with responses associated with protective immunity against Plasmodium. There was no significant association between schistosome-specific and Plasmodium-specific responses. Systemic cytokine levels rose with age as well as with schistosome infection and exposure. Overall the results show that (1) significantly more children are exposed to schistosome and Plasmodium infection than those currently infected and; (2) the development of protective acquired immunity commences in early childhood, although its effects on infection levels and pathology may take many years to become apparent.

Patterns in parasite epidemiology: the peak shift

A characteristic relationship between infection and host age, with levels of infection reaching a peak in particular age classes, has been reported for many parasites. However, several field studies have shown that this relationship is not invariant: if age-infection data are compared across host populations, the peak level of infection is higher and occurs at a younger age when the transmission rate is high, and is lower and occurs at an older age when it is low. This pattern is called the ;peak shift'. Here, Mark Woolhouse reviews the evidence for and the implications of the peak shift. The peak shift is consistent with the predictions of mathematical models that assume gradually acquired protective immunity, and this interpretation is supported by experimental studies using animals. This agreement between theory, experimental evidence and field studies strongly suggests that acquired immunity has a major impact on epidemiological patterns not only for parasites such as malaria, where the importance of acquired immunity is not in doubt, but also for many parasitic helminths, where the role of acquired immunity is less widely accepted.

Evidence for a peak shift in a humoral response to helminths: age profiles of IgE in the Shuar of Ecuador, the Tsimane of Bolivia, and the U.S. NHANES

BACKGROUND

The peak shift model predicts that the age-profile of a pathogen's prevalence depends upon its transmission rate, peaking earlier in populations with higher transmission and declining as partial immunity is acquired. Helminth infections are associated with increased immunoglobulin E (IgE), which may convey partial immunity and influence the peak shift. Although studies have noted peak shifts in helminths, corresponding peak shifts in total IgE have not been investigated, nor has the age-patterning been carefully examined across populations. We test for differences in the age-patterning of IgE between two South American forager-horticulturalist populations and the United States: the Tsimane of Bolivia (n=832), the Shuar of Ecuador (n=289), and the U.S. NHANES (n=8,336). We then examine the relationship between total IgE and helminth prevalences in the Tsimane.

METHODOLOGY/PRINCIPAL FINDINGS

Total IgE levels were assessed in serum and dried blood spots and age-patterns examined with non-linear regression models. Tsimane had the highest IgE (geometric mean =8,182 IU/ml), followed by Shuar (1,252 IU/ml), and NHANES (52 IU/ml). Consistent with predictions, higher population IgE was associated with steeper increases at early ages and earlier peaks: Tsimane IgE peaked at 7 years, Shuar at 10 years, and NHANES at 17 years. For Tsimane, the age-pattern was compared with fecal helminth prevalences. Overall, 57% had detectable eggs or larva, with hookworm (45.4%) and Ascaris lumbricoides (19.9%) the most prevalent. The peak in total IgE occurred around the peak in A. lumbricoides, which was associated with higher IgE in children <10, but with lower IgE in adolescents.

CONCLUSIONS

The age-patterning suggests a peak shift in total IgE similar to that seen in helminth infections, particularly A. lumbricoides. This age-patterning may have implications for understanding the effects of helminths on other health outcomes, such as allergy, growth, and response to childhood vaccination.

Differential recognition patterns of Schistosoma haematobium adult worm antigens by the human antibodies IgA, IgE, IgG1 and IgG4

Schistosoma haematobium antigen recognition profiles of the human isotypes IgA, IgE, IgG1 and IgG4 were compared by image analysis of western blots. Adult worm antigens separated by two-dimensional gel electrophoresis were probed with pooled sera from Zimbabweans resident in a S. haematobium endemic area, followed by the identification of individual antigenic parasite proteins using mass spectrometry. Overall, IgG1 reacted with the largest number of antigens, followed by IgE and IgA which detected the same number, while IgG4 detected the fewest antigens. IgE recognized all antigens reactive with IgG4 as well as an additional four antigens, an isoform of 28-kDa GST, phosphoglycerate kinase, actin 1 and calreticulin. IgG1 additionally recognized fatty acid–binding protein, triose-phosphate isomerase and heat shock protein 70, which were not recognized by IgA. Recognition patterns varied between some isoforms, e.g. the two fructose 1-6-bis-phosphate aldolase isoforms were differentially recognized by IgA and IgG1. Although the majority of S. haematobium adult worm antigens are recognized by all of the four isotypes, there are clear restrictions in antibody recognition for some antigens. This may partly explain differences observed in isotype dynamics at a population level. Differential recognition patterns for some isoforms indicated in the study have potential importance for vaccine development.

Schistosome infection intensity is inversely related to auto-reactive antibody levels

In animal experimental models, parasitic helminth infections can protect the host from auto-immune diseases. We conducted a population-scale human study investigating the relationship between helminth parasitism and auto-reactive antibodies and the subsequent effect of anti-helminthic treatment on this relationship. Levels of antinuclear antibodies (ANA) and plasma IL-10 were measured by enzyme linked immunosorbent assay in 613 Zimbabweans (aged 2-86 years) naturally exposed to the blood fluke Schistosoma haematobium. ANA levels were related to schistosome infection intensity and systemic IL-10 levels. All participants were offered treatment with the anti-helminthic drug praziquantel and 102 treated schoolchildren (5-16 years) were followed up 6 months post-antihelminthic treatment. ANA levels were inversely associated with current infection intensity but were independent of host age, sex and HIV status. Furthermore, after allowing for the confounding effects of schistosome infection intensity, ANA levels were inversely associated with systemic levels of IL-10. ANA levels increased significantly 6 months after anti-helminthic treatment. Our study shows that ANA levels are attenuated in helminth-infected humans and that anti-helminthic treatment of helminth-infected people can significantly increase ANA levels. The implications of these findings are relevant for understanding both the aetiology of immune disorders mediated by auto-reactive antibodies and in predicting the long-term consequences of large-scale schistosomiasis control programs.

The feasibility of MS and advanced data processing for monitoring Schistosoma mansoni infection

PURPOSE

Sensitive diagnosis, monitoring of disease progression and the evaluation of chemotherapeutic interventions are of prime importance for the improvement of control and prevention strategies for Schistosomiasis. The aim of the present study was to identify novel markers of Schistosoma mansoni infection and disease using urine samples from a large cohort from an area endemic for S. mansoni.

EXPERIMENTAL DESIGN

Urine samples were collected and processed on an automated sample clean-up and fractionation system combining strong cation exchange and reversed phase, and analyzed by MS (MALDI ToF MS). The ClinPro Tools(™) (CPT) software and the Discrete Wavelet Transformation-Support Vector Machine (DWT-SVM) procedure were used for classification and statistical analysis.

RESULTS

We observed a large difference in urinary peptide profiles between children and adults but classification based on infection was possible only for children. Here, in the external validation data set, 93% of the infected children were classified correctly with DWT-SVM (versus 76% for CPT). In addition 91% of low-infected children were classified correctly using DWT-SVM (versus 85% for CPT). The discriminating peptides were identified as fragments of collagen 1A1 and 1A3, and uromodulin.

CONCLUSIONS AND CLINICAL RELEVANCE

In conclusion, we provide the usefulness of a peptidomics profiling approach combined with DWT-SVM in the monitoring of S. mansoni infection.

Effect of treating Schistosoma haematobium infection on Plasmodium falciparum-specific antibody responses

BACKGROUND

The overlapping geographical and socio-economic distribution of malaria and helminth infection has led to several studies investigating the immunological and pathological interactions of these parasites. This study focuses on the effect of treating schistosome infections on natural human immune responses directed against plasmodia merozoite surface proteins MSP-1 (DPKMWR, MSP1(19)), and MSP-2 (CH150 and Dd2) which are potential vaccine candidates as well as crude malaria (schizont) and schistosome (whole worm homogenate) proteins.

METHODS

IgG1 and IgG3 antibody responses directed against Schistosoma haematobium crude adult worm antigen (WWH) and Plasmodium falciparum antigens (merozoite surface proteins 1/2 and schizont extract), were measured by enzyme linked immunosorbent assay (ELISA) in 117 Zimbabweans (6-18 years old) exposed to S. haematobium and P. falciparum infection. These responses were measured before and after anti-helminth treatment with praziquantel to determine the effects of treatment on anti-plasmodial/schistosome responses.

RESULTS

There were no significant associations between antibody responses (IgG1/IgG3) directed against P. falciparum and schistosomes before treatment. Six weeks after schistosome treatment there were significant changes in levels of IgG1 directed against schistosome crude antigens, plasmodia crude antigens, MSP-1(19), MSP-2 (Dd2), and in IgG3 directed against MSP-1(19). However, only changes in anti-schistosome IgG1 were attributable to the anti-helminth treatment.

CONCLUSION

There was no association between anti-P. falciparum and S. haematobium antibody responses in this population and anti-helminth treatment affected only anti-schistosome responses and not responses against plasmodia crude antigens or MSP-1 and -2 vaccine candidates.

Cytokine responses to Schistosoma haematobium in a Zimbabwean population: contrasting profiles for IFN-gamma, IL-4, IL-5 and IL-10 with age

BACKGROUND

The rate of development of parasite-specific immune responses can be studied by following their age profiles in exposed and infected hosts. This study determined the cytokine-age profiles of Zimbabweans resident in a Schistosoma haematobium endemic area and further investigated the relationship between the cytokine responses and infection intensity.

METHODS

Schistosome adult worm antigen-specific IFN-gamma, IL-4, IL-5 and IL-10 cytokine responses elicited from whole blood cultures were studied in 190 Zimbabweans exposed to S. haematobium infection (aged 6 to 40 years old). The cytokines were measured using capture ELISAs and the data thus obtained together with S. haematobium egg count data from urine assays were analysed using a combination of parametric and nonparametric statistical approaches.

RESULTS

Age profiles of schistosome infection in the study population showed that infection rose to peak in childhood (11-12 years) followed by a sharp decline in infection intensity while prevalence fell more gradually. Mean infection intensity was 37 eggs/10 ml urine (SE 6.19 eggs/10 ml urine) while infection prevalence was 54.7%. Measurements of parasite-specific cytokine responses showed that IL-4, IL-5 and IL-10 but not IFN-gamma followed distinct age-profiles. Parasite-specific IL-10 production developed early, peaking in the youngest age group and declining thereafter; while IL-4 and IL-5 responses were slower to develop with a later peak. High IL-10 producers were likely to be egg positive with IL-10 production increasing with increasing infection intensity. Furthermore people producing high levels of IL-10 produced little or no IL-5, suggesting that IL-10 may be involved in the regulation of IL-5 levels. IL-4 and IFN-gamma did not show a significant relationship with infection status or intensity and were positively associated with each other.

CONCLUSION

Taken together, these results show that the IL-10 responses develop early compared to the IL-5 response and may be down-modulating immunopathological responses that occur during the early phase of infection. The results further support current suggestions that the Th1/Th2 dichotomy does not sufficiently explain susceptibility or resistance to schistosome infection.

Age-adjusted Plasmodium falciparum antibody levels in school-aged children are a stable marker of microgeographical variations in exposure to Plasmodium infection

Background

Amongst school-aged children living in malaria endemic areas, chronic morbidity and exacerbation of morbidity associated with other infections are often not coincident with the presence or levels of Plasmodium parasitaemia, but may result from long-term exposure to the parasite. Studies of hepatosplenomegaly associated with Schistosoma mansoni infection and exposure to Plasmodium infection indicate that differences that occur over 1–2 km in levels of Plasmodium transmission are related to the degree of exacerbation of hepatosplenomegaly and that Plasmodium falciparum schizont antigen (Pfs)-IgG3 levels may be a marker for the differing levels of exposure.

Methods

To investigate the validity of Pfs-IgG3 measurements as a tool to assess these comparative exposure levels on a microgeographical scale, cross-sectional community surveys were conducted over a 10 × 6 km study site in Makueni District, Kenya, during low and high malaria transmission seasons. During both high and low malaria transmission seasons, thick blood smears were examined microscopically and circulating Pfs-IgG3 levels measured from dried blood spot elute. GIS techniques were used to map prevalence of parasitaemia and Pfs-IgG3 levels.

Results

Microgeographical variations in prevalence of parasitaemia were observed during the high but not the low transmission season. Pfs-IgG3 levels were stable between high and low transmission seasons, but increased with age throughout childhood before reaching a plateau in adults. Adjusting Pfs-IgG3 levels of school-aged children for age prior to mapping resulted in spatial patterns that reflected the microgeographical variations observed for high season prevalence of parasitaemia, however, Pfs-IgG3 levels of adults did not. The distances over which age-adjusted Pfs-IgG3 of school-aged children fluctuated were comparable with those distances over which chronic morbidity has previous been shown to vary.

Conclusion

Age-adjusted Pfs-IgG3 levels of school-aged children are stable and when mapped can provide a tool sensitive enough to detect microgeographical variations in malaria exposure, that would be useful for studying the aetiology of morbidities associated with long-term exposure and co-infections.

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

We examined associations between schistosome-specific antibody responses and reinfection in Senegalese individuals recently exposed to Schistosoma mansoni. The effects of treatment, age, intensity of infection and duration of exposure on schistosome-specific antibody responses were also investigated by comparing immune responses in individuals exposed for less than 3 years with responses in people exposed for more than 8 years. All individuals were bled before treatment as well as 6 and 12 weeks after. We used a statistical model that included interaction terms between time, age, infection intensity and duration of exposure. The overall patterns of most specific antibody responses by age were similar to those previously published for S. mansoni, Schistosoma japonicum and Schistosoma haematobium infections in different endemic areas. In general, a boost in specific antibody responses against adult worm antigen (SWA) was observed at 6 weeks after treatment whereas the majority of isotype responses against egg antigen (SEA) were not affected by treatment. Our analysis showed that the effect of treatment on schistosome-specific antibody responses is influenced by age, infection intensity and duration of exposure. We found no evidence that treatment matures the specific antibody response of children recently infected with S. mansoni. Our results indicate that the build-up of potentially protective immunoglobulin E (IgE) responses was associated with duration of exposure, or, in other words, experience of infection. Interestingly, in recently exposed individuals there was a significant association between IgA responses to SWA and resistance to reinfection. Resistance to reinfection and production of IgA-SWA was associated with adulthood independently of exposure patterns, suggesting that susceptibility to S. mansoni and the development of protective immune responses is age-dependent.

Prevalence of urinary schistosomiasis and HIV in females living in a rural community of Zimbabwe: does age matter?

A cross-sectional study was conducted on 544 women living in Mupfure rural area of Zimbabwe to determine whether infection with urinary schistosomiasis is associated with HIV infection. Schistosoma haematobium infection was examined in urine samples and HIV infection was determined in sera. The prevalence of S. haematobium infection was highest (60%) in women below 20 years of age and declined to 29% in the oldest age group (test for trends, P<0.001). Overall, women infected with urinary schistosomiasis had an HIV prevalence of 33.3%, whilst women without urinary schistosomiasis had an HIV prevalence of 25.6% (chi(2), P=0.053). Women above the age of 35 years and infected with urinary schistosomiasis had a significantly higher HIV prevalence (37.5%) than those without urinary schistosomiasis (16.8%; chi(2), P<0.001).

Immuno-epidemiology of human Schistosoma haematobium infection: preferential IgG3 antibody responsiveness to a recombinant antigen dependent on age and parasite burden

Background

Schistosomiasis is a major parasitic disease affecting over 200 million people in the developing world with a further 400 million people at risk of infection. The aim of this study was to identify a single antigen from adult Schistosoma haematobium worms and subsequently use this antigen to study the development of schistosome-acquired immunity in a human population.

Methods

The full-length cDNA sequence of a S. haematobium protein, a putative orthologue of the S. mansoni tegumental antigen Sm13, was obtained from a cDNA library of adult S. haematobium worms and named Sh13 following a small-scale expressed sequence tags (EST) project. The recombinant Sh13 protein expressed in E. coli, was used to investigate immuno-epidemiological patterns in 147 Zimbabweans (7–18 years old) exposed to S. haematobium.

Results

Sequence analysis of the full-length cDNA sequence of the S. haematobium protein Sh13, indicated that the protein has an N-terminal signal peptide and encodes an 85-amino acid mature protein with a highly conserved predicted transmembrane domain (86 % identity with the S. mansoni tegumental antigen Sm13). The recombinant Sh13 protein was used in ELISA assays to determine the reactivity of sera from the study participants. Antibody responses against Sh13 were predominantly IgG3 isotype compared to responses against crude worm antigens which were predominantly IgG1 and IgG4. The relationship between anti-Sh13 IgG3 levels and infection intensity varied significantly with host age. The youngest children (7–10 years old) had relatively low levels of both infection and anti-Sh13 IgG3. In older children (11–12 years old) rising infection levels were accompanied by a significant increase in anti-Sh13 IgG3 levels. Subsequently, infection intensity declined significantly in 13–18 year olds but levels of the antibody continued to rise. The changing relationship between infection intensity and anti-Sh13 IgG3 levels with host age is consistent with the profile of a protective immune response predicted from theoretical work.

Conclusion

We have identified and characterised a novel S. haematobium antigen Sh13, a putative tegumental protein, and shown that it is recognised predominantly by IgG3 antibodies from people infected with/exposed to S. haematobium parasites. We have also shown that, the anti-Sh13 IgG3 response is maximal in older individuals with the lowest infection intensity, and that the age profile of the relationship between anti-Sh13 IgG3 and infection intensity is consistent with that predicted by theoretical work for a protective response stimulated by and directed against adult worms.

Cytokine production in whole blood cultures from a fishing community in an area of high endemicity for Schistosoma mansoni in Uganda: the differential effect of parasite worm and egg antigens

The human host is continuously exposed to the egg and the adult worm developmental stages of Schistosoma mansoni during chronic infections with the parasite. To assess the cytokine responses induced by these different costimulating stages and how they are influenced by host age and infection intensity, whole blood samples from a cross-sectional cohort of 226 members of a Ugandan fishing community who had been resident in an area with high transmission of S. mansoni for the previous 10 years or from birth were stimulated with S. mansoni egg antigen (SEA) or worm antigen (SWA). SWA-specific gamma interferon (IFN-gamma) production increased with age, and the levels of SWA- and SEA-specific interleukin 3 (IL-3) were weakly correlated with schistosome infection intensity. The production of most cytokines was little affected by age or infection intensity but was either SEA or SWA specific. One hundred thirty-two members of the cohort coproduced IL-5 and IL-13 specifically in response to SWA, whereas only 15 produced these cytokines, and at much lower levels, in response to SEA. IL-10, IL-4, and IFN-gamma were also produced in response to SWA, whereas the response to SEA consisted almost exclusively of IL-10. Our results suggest that, in contrast to what has been described for the murine model of S. mansoni and during acute human infections, chronic intense exposure to and infection with S. mansoni in this cohort resulted in very low levels of response to SEA in vitro in the presence of a vigorous and mixed Th1-Th2 response to SWA.

Contrasting cellular responses in Schistosoma haematobium infected and exposed individuals from areas of high and low transmission in Zimbabwe

The study compared cytokine profiles of individuals from two areas with different transmission patterns for Schistosoma haematobium. One area was a high transmission (HT) while the other was a low transmission (LT) area for S. haematobium. Observations on cellular immune responses were made on stimulated peripheral blood mononuclear cells (PBMC), which were collected pre-treatment, then at 12 and 18 months post treatment. Stimulation was with schistosome worm and egg antigens and a mitogen, phaetohaemaglutinin (PHA). Observations were made on PBMC proliferation and the profiles of cytokine produced over a 5-day incubation period. The two distinct areas showed significant differences on both levels of proliferation and cytokine production for all the measured classes (IL-4, IL-5, IL-10 and IFN-gamma). PBMC from individuals from the LT area had high levels of proliferation but low cytokine production to both antigen stimulants while PBMC from individuals from the HT area showed low levels of proliferation but high cytokine production levels. Prior to treatment, individuals not excreting schistosome ova in the HT area had higher levels of proliferation to the stimulants, than the infected individuals. However, after treatment re-infected individuals showed high levels of proliferation. Before treatment, both infected and uninfected groups showed low and similar ratios, respectively, of IL-4:IFN-gamma, IL-5:IFN-gamma and IL-10:IFN-gamma, while IFN-gamma was high in the infected individuals. After treatment the non re-infected had higher levels of IL-4, IL-5 and IL-10, with the infected having high levels of IFN-gamma. Th1-like response dominated during infection with the Th2-like responses dominating post treatment and in uninfected individuals. The results indicated that the cytokine balance determines, in part, susceptibility or resistance to S. haematobium infection.

The relationship between age, sex, egg-count and specific antibody responses against Schistosoma mansoni antigens in a Ugandan fishing community

In schistosomiasis endemic areas, antibody isotype responses against Schistosoma mansoni antigens vary with host age, sex and duration or intensity of infection, and are associated with susceptibility or resistance to infection. Identifying the quality and quantity of these responses is important to our understanding of the host-parasite relationship; however, the various host and parasite factors have a strong tendency to confound each other. We investigated the relationships and interactions between age, sex, faecal egg-counts and specific antibody isotype (IgA, IgG1, IgG2, IgG3, IgG4, IgE, IgM) responses to S. mansoni worm (SWA) and egg (SEA) antigens, amongst 380 individuals aged 5-59 from a fishing community from Uganda. This community was characterized by high levels of exposure, and high infection intensities, with higher infection intensities in males than in females. Multivariate anova was conducted with interaction terms between the three categorized explanatory variables. Most anti-SWA responses increased with age, whereas anti-SEA responses tended to decline with age, especially after puberty. IgG1-SWA, IgG4-SWA, IgG4-SEA, IgE-SWA responses increased with egg count, whereas IgG2-SEA decreased with egg count. IgG1-SWA, IgG4-SWA, IgE-SWA and IgG4-SEA responses were independently higher in males, whereas IgG2-SEA responses were independently higher in females. The significant effects of sex on isotype responses to adult worm antigens may be partly because of different levels of cumulative exposure. IgG4-SEA and IgG4-SWA were both strongly correlated with egg count. Patterns of IgE-SWA responses were qualitatively different to IgG4 responses, suggesting independent pathways of regulation.

The effect of treatment on the age-antibody relationship in children infected with Schistosoma mansoni and Schistosoma haematobium

The effect of praziquantel treatment on the age-antibody relationship was studied in 174 children aged between 6 and 17 years from a schistosome endemic area in Zimbabwe. The children were co-infected with Schistosoma mansoni and S. haematobium with infection prevalences of 74% and 53% respectively. Antibody levels for the isotypes IgA, IgE, IgM, IgG1, IgG2, IgG3 and IgG4, directed against soluble egg antigen were measured using an indirect ELISA assay. Treatment resulted in a significant increase in levels of IgG2 and IgG3 while levels of IgA decreased significantly. In untreated children there were significant decreases in levels of IgG4. Treatment also resulted in significant alteration in the age-antibody profiles for the isotypes IgE, IgM, IgG1 and IgG2 in treated children but not in untreated children. The results are discussed in the context of factors believed to give rise to the age-antibody relationship; i.e. age-related exposure patterns, age-related development of acquired immunity, age-related hormonal changes and age-related changes in innate susceptibility to infection.

The impact of repeated treatment with praziquantel of schistosomiasis in children under six years of age living in an endemic area for Schistosoma haematobium infection

Praziquantel was given every eight weeks for two years to children aged under six years of age, living in a Schistosoma haematobium endemic area. Infection with S. haematobium and haematuria were examined in urine and antibody profiles (IgA, IgE, IgM, IgG1, IgG2, IgG3, and IgG4) against S. haematobium adult worm and egg antigens were determined from sera collected before each treatment. Chemotherapy reduced infection prevalence and mean intensity from 51.8% and 110 eggs per 10 ml urine, respectively, before starting re-treatment programme to very low levels thereafter. Praziquantel is not accumulated after periodic administration in children. Immunoglobulin levels change during the course of treatment with a shift towards 'protective' mechanisms. The significant changes noted in some individuals were the drop in 'blocking' IgG2 and IgG4 whereas the 'protecting' IgA and IgG1 levels increased. The antibody profiles in the rest of the children remained generally unchanged throughout the study and no haematuria was observed after the second treatment. The removal of worms before production of large number of eggs, prevented the children from developing morbidity.

Human T- and B-cell responses to Schistosoma mansoni recombinant glyceraldehyde 3-phosphate dehydrogenase correlate with resistance to reinfection with S. mansoni or Schistosoma haematobium after chemotherapy

Recently we reported that human T- and B-cell recognition of a 42-kDa protein (p42) in soluble extracts of adult Schistosoma mansoni worms correlates with resistance to reinfection with S. mansoni or S. haematobium. Amino acid microsequencing of p42 revealed that it consists predominantly of schistosome glyceraldehyde 3-phosphate dehydrogenase (SG3PDH). We have expressed SG3PDH in Escherichia coli and purified the recombinant protein in a soluble and enzymatically active form. Recombinant SG3PDH (rSG3PDH) reacted with human monospecific antibodies to p42. Lymphoproliferation and production of interleukin-4 and gamma interferon (IFN-gamma) after in vitro stimulation with rSG3PDH and serum isotype responses to rSG3PDH were examined in individuals with extremes of resistance and susceptibility to reinfection after treatment of previous S. mansoni or S. haematobium infection. Lymphoproliferation and IFN-gamma production in response to rSG3PDH and the presence of serum immunoglobulin G1 (IgG1), IgG3, and IgA antibodies to rSG3PDH generally characterized individuals who are resistant to reinfection after chemotherapy. The data indicate that T- and B-cell immune reactivity to rSG3PDH correlates with resistance to reinfection, confirming previous studies identifying SG3PDH as a target of protective immunity in humans, and suggest that SG3PDH should be investigated as a possible vaccine for human schistosomiasis.

Paramyosin is a major target of the human IgA response against Schistosoma japonicum

Human resistance and susceptibility to schistosomiasis is associated with age and specific antibody isotype responses against worm (SWAP) and egg (SEA) antigens. In a cross-sectional study of 176 individuals infected with Schistosoma japonicum in the Philippines, strikingly similar isotype response patterns against SWAP and SEA was observed when compared to other endemic areas. Interestingly, IgA titres to SWAP correlated with older age among S. japonicum-infected individuals (n = 176, P < 0.01), suggesting a role for this isotype in protective immunity. To identify the molecular targets of human IgA, 17 high-IgA/SWAP responders were identified from the said population. IgA antibodies from the majority (14/17) of these individuals recognized a band of 97 kDa (Sj97), comigrating in immunoblots with the myofibrillar protein paramyosin. The antigen was confirmed as paramyosin by expressed sequence tag (EST)-analysis of four clones obtained by screening an adult S. japonicum cDNA library with pooled IgA antisera and mouse antiparamyosin polyclonal antibodies. The identification of paramyosin as a major target of human IgA raises its potential as a vaccine candidate that targets mucosal immune responses. Since this antigen is exposed on the parasite surface only during the lung stages, we propose that human IgA contributes to parasite attrition during schistosome migration in the lungs.

Development of antibody isotype responses to Schistosoma mansoni in an immunologically naive immigrant population: influence of infection duration, infection intensity, and host age

We have identified the influence of host and parasite factors that give rise to characteristic antibody isotype profiles with age seen in human populations living in different areas of schistosomiasis endemicity. This is important in the immunobiology of this disease. It is also of interest in the context of human responses to chronic antigen stimulation, vaccines, allergens, and other pathogens. In populations exposed to endemic schistosomiasis, factors such as intensity and duration of infection are age dependent. They therefore confound the influence of host age on antiparasite responses. Here, we resolved these confounding factors by comparing the developing antibody responses of an immunologically naive immigrant population as they acquired the infection for the first time with those of chronically infected resident inhabitants of the same region of Schistosoma mansoni endemicity in Kenya. Recent arrival in the area strongly favored immunoglobulin G3 (IgG3) responses against the parasite. The antibody isotype responses associated with human susceptibility to reinfection after chemotherapy were elevated in those suffering high intensities of infection (IgG4 responses against worm and egg antigens) or were characteristic responses of young children irrespective of the intensity or duration of infection (IgG2 responses against egg antigen). IgE responses against the adult worm, a response associated with resistance to reinfection after chemotherapy, increased with the ages of infected individuals and were also favored in those currently suffering higher intensities of infection.

A comparison of re-infection rates with Schistosoma haematobium following chemotherapy in areas with high and low levels of infection

Two groups of children (6-15 years) from a Schistosoma haematobium endemic area were followed for 9 months after praziquantel treatment. Seventy-three children came from an area of high infection while 67 children came from an area of low infection. Pre-treatment infection prevalence in the high infection area (76.6%) was significantly higher than that in low infection area (36.3%). Levels of anti-SEA immunoglobulin (Ig)A and IgM were significantly higher and levels of IgG3 significantly lower in children from the low infection area. Nine months after treatment, infection prevalence was significantly higher in the high infection area (29.0%) (where re-infection rates were higher) than in the low infection area (12.9%). Children from the high infection area were six times more likely to get re-infected than those from the low infection area, while younger children were 30 times more likely to get re-infected than older children. These results are discussed in relation to differences in transmission and the development of acquired immunity. Pre-treatment levels of IgM and the difference between IgE and IgG4 were positively associated with re-infection in the high infection area. These results are discussed in relation to the interpretation of simple correlations between infection and some antibody levels and the inference of causal relationships between observed epidemiological and immunological patterns.

Systemic and mucosal immune responses after intranasal administration of recombinant Mycobacterium bovis bacillus Calmette-Guérin expressing glutathione S-transferase from Schistosoma haematobium

A major goal of current vaccine development is the induction of strong immune responses against protective antigens delivered by mucosal routes. One of the most promising approaches in that respect relies on the use of live recombinant vaccine carriers. In this study, Mycobacterium bovis BCG was engineered to produce an intracellular glutathione S-transferase from Schistosoma haematobium (Sh28GST). The gene encoding Sh28GST was placed under the control of the mycobacterial hsp60 promoter on a replicative shuttle plasmid containing a mercury resistance operon as the only selectable marker. The recombinant Sh28GST produced in BCG bound glutathione and expressed enzymatic activity, indicating that its active site was properly folded. Both intraperitoneal and intranasal immunizations of BALB/c mice with the recombinant BCG resulted in strong anti-Sh28GST antibody responses, which were enhanced by a boost. Mice immunized intranasally produced a mixed response with the production of Sh28GST-specific immunoglobulin G1 (IgG1), IgG2a, IgG2b, and IgA in the serum. In addition, high levels of anti-Sh28GST IgA were also found in the bronchoalveolar lavage fluids, demonstrating that intranasal delivery of the recombinant BCG was able to induce long-lasting secretory and systemic immune responses to antigens expressed intracellularly. Surprisingly, intranasal immunization with the BCG producing the Sh28GST induced a much stronger specific humoral response than intranasal immunization with BCG producing the glutathione S-transferase from Schistosoma mansoni, although the two antigens have over 90% identity. This difference was not observed after intraperitoneal administration.