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

Malaria, Urogenital Schistosomiasis, and Anaemia in Pregnant Ghanaian Women

Background

Anaemia is common in sub-Saharan Africa, and parasitic infections could worsen its burden during pregnancy. Moreover, women become susceptible to malaria during pregnancy. We investigated Plasmodium falciparum (P. falciparum) and Schistosoma haematobium (S. haematobium) infections and determined their association with anaemia during pregnancy.

Methods

A cross-sectional study involving 707 pregnant women attending antenatal care visits (ANC) and 446 at delivery was conducted in Battor and Adidome hospitals. Pregnant women were screened by microscopy and qPCR for P. falciparum and S. haematobium infections. Haemoglobin (Hb) levels were determined, and most participants received intermittent preventive treatment during pregnancy (IPTp) during ANC till delivery. Regression analyses were performed for associations between parasite infection and anaemia.

Results

P. falciparum microscopy prevalence at ANC and delivery was 8% and 2%, respectively, and by PCR 24% at ANC and 12% at delivery. Anaemia prevalence at ANC was 52% and 49% at delivery. There was an increased risk of anaemia with P. falciparum infection (aOR = 1.92; p = 0.04). IPTp (p = 0.003) and age (p = 0.004) were associated with increased Hb levels at delivery. S. haematobium prevalence by microscopy was 4% at ANC and 2% at delivery. No significant correlation between S. haematobium and Hb levels was observed (coef. = -0.62 g/dl; p = 0.07).

Conclusion

High anaemia prevalence was observed during pregnancy, and P. falciparum infection was associated with anaemia at ANC. Low S. haematobium prevalence could be attributed to previous praziquantel treatment during mass drug administration. Routine diagnosis and treatment of S. haematobium infections in endemic areas could be initiated to reduce schistosomiasis during pregnancy.

Humoral antimalaria immune response in Nigerian children exposed to helminth and malaria parasites

Background

Malaria and helminthic parasites are endemic in tropical countries, and co-infections might influence host-parasite interactions. In this community-based cross-sectional study, the effect that the presence of soil-transmitted helminths (STH) (Hookworm, Hymenolepis nana) and Schistosoma haematobium infections could have on the immunoglobulin (Ig) candidate protein of the malaria vaccine GMZ2 levels was evaluated.

Methods

Blood, stool, and urine samples were collected from 5-15-year-old children to diagnose P. falciparum (Pf), STH, and Schistosoma haematobium, respectively. Identification and quantification of the parasite load of STH and S. haematobium were achieved by light microscopy. A polymerase chain reaction was carried out to detect submicroscopic infections of P. falciparum. Plasma levels of GMZ2 specific IgG and its subclasses were quantified by ELISA.

Results

The median level of total IgG in individuals with co-infection with Pf/H. nana was significantly lower in the mono-infected group with Pf (p = 0.0121) or study participants without infection (p=0.0217). Similarly, the median level of IgG1 was statistically lower in Pf/H. nana group compared to Pf-group (p=0.0137). Equally, the Pf/H. nana infected individuals posted a lower level of IgG1 compared to Pf-group (p=0.0137) and IgG4 compared to the Pf-group (p=0.0144). Spearman rank correlation analyses indicated positive relationships between the densities of H. nana (ρ=0.25, p=0.015) and S. haematobium (ρ=0.36, p<0.0001).

Conclusions

Hookworm and H. nana infections are associated with reduced GMZ2 specific IgG levels. This study shows the possible manipulation of immune responses by helminths for their survival and transmission, which may have serious implications for vaccine development and deployment in helminth-endemic regions.

Association of anthelmintic treatment with malaria prevalence, incidence, and parasitemia: A systematic review and meta-analysis

A chronic helminth infection can alter host immune response and affect malaria infection. We conducted a systematic review and meta-analysis to find the impact of anthelmintic treatment on malaria prevalence, incidence, and parasitemia. Nine and 12 electronic databases were searched on 28^th July 2015 and 26^th June 2020 for relevant studies. We performed meta-analysis for malaria prevalence, incidence, parasitemia, and a qualitative synthesis for other effects of anthelmintic treatment. Seventeen relevant papers were included. There was no association between anthelmintic treatment and malaria prevalence or change of parasitemia at the end of follow up period (pooled OR 0.93, 95% CI: 0.62, 1.38, p-value=0.71 and SMD -0.08, 95%CI: -0.24, 0.07, p-value=0.30 respectively) or at any defined time points in analysis. Pooled analysis of three studies demonstrated no association between malaria incidence and anthelmintic treatment (rate ratio 0.93, 95%CI: 0.80, 1.08, p-value=0.33). Our study encourages anthelmintic treatment in countries with high burden of co-infections as anthelmintic treatment is not associated with change in malaria prevalence, incidence, or parasitemia.

Effect of hookworm infection and anthelmintic treatment on naturally acquired antibody responses against the GMZ2 malaria vaccine candidate and constituent antigens

Background

Malaria and helminths diseases are co-endemic in most parts of sub-Saharan Africa. Immune responses from each of these pathogens interact, and these interactions may have implications on vaccines. The GMZ2 malaria vaccine candidate is a fusion protein of Plasmodium falciparum merozoite surface protein 3 (MSP3) and glutamate rich protein (GLURP R0). GMZ2 has recently showed modest efficacy in a phase IIb multicenter trial. Here, we assessed the effect of hookworm (Necator americanus) infection and anthelmintic treatment on naturally acquired antibody responses against GMZ2 and constituent antigens.

Methods

This longitudinal cross-sectional study was conducted in the Kintampo North Municipality of Ghana. Blood and stool samples were taken from 158 individuals (4–88 years old) infected with either P. falciparum alone (n = 59) or both hookworm and P. falciparum (n = 63) and uninfected endemic controls (n = 36). Stool hookworm infection was detected by the Kato-Katz method and PCR. Malaria parasitaemia was detected by RDT, light microscopy and P. falciparum-specific 18S rRNA gene PCR. Serum samples were obtained prior to hookworm treatment with a single dose of albendazole (400 mg) and 3 weeks (21 days) after treatment. Levels of IgG1, IgG3 and IgM against GMZ2, MSP3 and GLURP R0 were measured by ELISA and compared among the groups, before and after treatment.

Results

Participants with P. falciparum and hookworm co-infection had significantly higher IgG3 levels to GMZ2 than those with only P. falciparum infection and negative control (p < 0.05) at baseline. Treatment with albendazole led to a significant reduction in IgG3 levels against both GMZ2 and GLURP R0. Similarly, IgM and IgG1 levels against MSP3 also decreased following deworming treatment.

Conclusion

Individuals with co-infection had higher antibody responses to GMZ2 antigen. Treatment of hookworm/malaria co-infection resulted in a reduction in antibody responses against GMZ2 and constituent antigens after albendazole treatment. Thus, hookworm infection and treatment could have a potential implication on malaria vaccine efficacy.

Cytokine profiles of Necator americanus and Plasmodium falciparum co-infected patients in rural Ghana

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Co-infection of hookworm with P. falciparum modulates blood parasitemia levels.

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Cytokine levels were higher in the parasite infected individuals.

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Serum eotaxin level correlate negatively with hookworm intensity.

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Deworming drug treatment alters cytokine profiles in hookworm infected subjects.

Background

Necator americanus (hookworm) and Plasmodium falciparum co-infections are common in endemic communities in rural Ghana. Human immune responses to P. falciparum and hookworm are complex, and the dynamics of cytokine levels and effector mediators are poorly understood. This study aimed to determine the effect of hookworm and P. falciparum co-infection on parasite intensities and cytokine profiles in individuals before and after deworming drug treatment.

Methods

In this cross-sectional study conducted in the Kintampo North Municipality of Ghana blood and stool samples were analyzed from 984 participants (aged 4–88 years). Stool samples were collected at baseline from all participants and examined for the presence of hookworm using the Kato-Katz method. Blood and stool samples were analysed again two weeks after albendazole treatment of hookworm infected individuals. Malaria parasitaemia was estimated by light microscopy and P. falciparum-specific 18S rRNA gene PCR method used for species identification. Serum levels of circulating cytokines interleukins -5, -10 (IL-5, IL-10), tumor necrosis factor [TNF]-α, and eotaxin [CCL11] were determined using ELISA based methods.

Results

Malaria parasitaemia was significantly reduced in hookworm and P. falciparum co-infected individuals (p = 0.0018) while hookworm intensity was similar between groups. IL-10 level was significantly higher in the co-infected individuals (39.9 ± 12.2 pg/ml) compared to the single infected or the uninfected group (10.7 ± 7.6 mg/ml). IL-5 level was higher in the hookworm only infected individual. TNF-α levels were higher in all infected groups compared to the uninfected controls. CCL11 levels were significantly higher in subjects infected with hookworm only or co-infected with hookworm and P. falciparum. There was a significantly negative correlation (r_s = −0.39, p = 0.021) between hookworm eggs per gram of stool and CCL11 levels in the group mono-infected with hookworm which was not affected by treatment. Treatment with albendazole led to a significant reduction of TNF-α (p = 0.041), IL-5 (p = 0.01) and IL-10 (p = 0.001) levels.

Conclusion

This study shows that in the absence of other helminths, co-infection of hookworm with P. falciparum may modulate blood parasitemia levels and cytokine responses. Data also show that deworming drug treatment alters these cytokine profiles in hookworm infected subjects. Future studies to elucidate the potential mechanisms underlying these observations should include an assessment of parasite specific cellular responses.

Comparative Assessment of Health Benefits of Praziquantel Treatment of Urogenital Schistosomiasis in Preschool and Primary School-Aged Children

Schistosomiasis is a major public health problem in Africa. However, it is only recently that its burden has become recognised as a significant component impacting on the health and development of preschool-aged children. A longitudinal study was conducted in Zimbabwean children to determine the effect of single praziquantel treatment on Schistosoma haematobium-related morbidity markers: microhaematuria, proteinuria, and albuminuria. Changes in these indicators were compared in 1-5 years versus 6-10 years age groups to determine if treatment outcomes differed by age. Praziquantel was efficacious at reducing infection 12 weeks after treatment: cure rate = 94.6% (95% CI: 87.9-97.7%). Infection rates remained lower at 12 months after treatment compared to baseline in both age groups. Among treated children, the odds of morbidity at 12 weeks were significantly lower compared to baseline for proteinuria: odds ratio (OR) = 0.54 (95% CI: 0.31-0.95) and albuminuria: OR = 0.05 (95% CI: 0.02-0.14). Microhaematuria significantly reduced 12 months after treatment, and the effect of treatment did not differ by age group: OR = 0.97 (95% CI: 0.50-1.87). In conclusion, praziquantel treatment has health benefits in preschool-aged children exposed to S. haematobium and its efficacy on infection and morbidity is not age-dependent.

Malaria endemicity and co-infection with tissue-dwelling parasites in Sub-Saharan Africa: a review

Mechanisms and outcomes of host-parasite interactions during malaria co-infections with gastrointestinal helminths are reasonably understood. In contrast, very little is known about such mechanisms in cases of malaria co-infections with tissue-dwelling parasites. This is lack of knowledge is exacerbated by misdiagnosis, lack of pathognomonic clinical signs and the chronic nature of tissue-dwelling helminthic infections. A good understanding of the implications of tissue-dwelling parasitic co-infections with malaria will contribute towards the improvement of the control and management of such co-infections in endemic areas. This review summarises and discusses current information available and gaps in research on malaria co-infection with gastro-intestinal helminths and tissue-dwelling parasites with emphasis on helminthic infections, in terms of the effects of migrating larval stages and intra and extracellular localisations of protozoan parasites and helminths in organs, tissues, and vascular and lymphatic circulations.

Identifying and evaluating field indicators of urogenital schistosomiasis-related morbidity in preschool-aged children

BACKGROUND

Several studies have been conducted quantifying the impact of schistosome infections on health and development in school-aged children. In contrast, relatively little is known about morbidity levels in preschool-aged children (≤ 5 years) who have been neglected in terms of schistosome research and control. The aim of this study was to compare the utility of available point-of-care (POC) morbidity diagnostic tools in preschool versus primary school-aged children (6-10 years) and determine markers which can be used in the field to identify and quantify Schistosoma haematobium-related morbidity.

METHODS/PRINCIPAL FINDINGS

A comparative cross-sectional study was conducted to evaluate the performance of currently available POC morbidity diagnostic tools on Zimbabwean children aged 1-5 years (n=104) and 6-10 years (n=194). Morbidity was determined using the POC diagnostics questionnaire-based reporting of haematuria and dysuria, clinical examination, urinalysis by dipsticks, and urine albumin-to-creatinine ratio (UACR). Attributable fractions were used to quantify the proportion of morbidity attributable to S. haematobium infection. Based on results of attributable fractions, UACR was identified as the most reliable tool for detecting schistosome-related morbidity, followed by dipsticks, visual urine inspection, questionnaires, and lastly clinical examination. The results of urine dipstick attributes showed that proteinuria and microhaematuria accounted for most differences between schistosome egg-positive and negative children (T=-50.1; p<0.001). These observations were consistent in preschool vs. primary school-aged children.

CONCLUSIONS/SIGNIFICANCE

Preschool-aged children in endemic areas can be effectively screened for schistosome-related morbidity using the same currently available diagnostic tools applicable to older children. UACR for detecting albuminuria is recommended as the best choice for rapid assessment of morbidity attributed to S. haematobium infection in children in the field. The use of dipstick microhaematuria and proteinuria as additional indicators of schistosome-related morbidity would improve the estimation of disease burden in young children.

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.

Coinfection with Plasmodium falciparum and Schistosoma haematobium: additional evidence of the protective effect of Schistosomiasis on malaria in Senegalese children

Parasitic infections are associated with high morbidity and mortality in developing countries. Several studies focused on the influence of helminth infections on malaria but the nature of the biological interaction is under debate. Our objective was to undertake a study to explore the influence of the measure of excreted egg load caused by Schistosoma haematobium on Plasmodium falciparum parasite densities. Ten measures of malaria parasite density and two measures of schistosomiasis egg urinary excretion over a 2-year follow-up period on 178 Senegalese children were considered. A linear mixed-effect model was developed to take data dependence into account. This work showed that children with a light S. haematobium infection (1-9 eggs/mL of urine) presented lower P. falciparum parasite densities than children not infected by S. haematobium (P < 0.04). Possible changes caused by parasite coinfections should be considered in the anti-helminth treatment of children and in malaria vaccination development.

Immunological consequences of antihelminthic treatment in preschool children exposed to urogenital schistosome infection

Urogenital schistosomiasis, due to Schistosoma haematobium, is endemic in sub-Saharan Africa. Control is by targeted treatment with praziquantel but preschool age children are excluded from control programs. Immunological studies on the effect of treatment at this young age are scarce. In light of studies in older individuals showing that praziquantel alters antischistosome immune responses and responses to bystander antigens, this study aims to investigate how these responses would be affected by treatment at this young age. Antibody responses directed against schistosome antigens, Plasmodium falciparum crude and recombinant antigens, and the allergen house dust mite were measured in children aged 3 to 5 years before and 6 weeks after treatment. The change in serological recognition of schistosome proteins was also investigated. Treatment augmented antischistosome IgM and IgE responses. The increase in IgE responses directed against adult worm antigens was accompanied by enhanced antigen recognition by sera from the children. Antibody responses directed against Plasmodium antigens were not significantly affected by praziquantel treatment nor were levels of allergen specific responses. Overall, praziquantel treatment enhanced, quantitatively and qualitatively, the antiworm responses associated with protective immunity but did not alter Plasmodium-specific responses or allergen-specific responses which mediate pathology in allergic disease.

Schistosoma mansoni infection impairs antimalaria treatment and immune responses of rhesus macaques infected with mosquito-borne Plasmodium coatneyi

Malaria and schistosomiasis are the world's two most important parasitic infections in terms of distribution, morbidity, and mortality. In areas where Plasmodium and Schistosoma species are both endemic, coinfections are commonplace. Mouse models demonstrate that schistosomiasis worsens a malaria infection; however, just as mice and humans differ greatly, the murine-infecting Plasmodium species differ as much from those that infect humans. Research into human coinfections (Schistosoma haematobium-Plasmodium falciparum versus Schistosoma mansoni-P. falciparum) has produced conflicting results. The rhesus macaque model provides a helpful tool for understanding the role of S. mansoni on malaria parasitemia and antimalarial immune responses using Plasmodium coatneyi, a malaria species that closely resembles P. falciparum infection in humans. Eight rhesus macaques were exposed to S. mansoni cercariae. Eight weeks later, these animals plus 8 additional macaques were exposed to malaria either through bites of infected mosquitos or intravenous inoculation. When malaria infection was initiated from mosquito bites, coinfected animals displayed increased malaria parasitemia, decreased hematocrit levels, and suppressed malaria-specific antibody responses compared to those of malaria infection alone. However, macaques infected by intravenous inoculation with erythrocytic-stage parasites did not display these same differences in parasitemia, hematocrit, or antibody responses between the two groups. Use of the macaque model provides information that begins to unravel differences in pathological and immunological outcomes observed between humans with P. falciparum that are coinfected with S. mansoni or S. haematobium. Our results suggest that migration of malaria parasites through livers harboring schistosome eggs may alter host immune responses and infection outcomes.

Advances in our understanding of the epidemiology of Plasmodium and schistosome infection: informing coinfection studies

PURPOSE OF REVIEW

Schistosomes and Plasmodium parasites have complex patterns of transmission, leading to differing dynamics of host-parasite interactions across study sites and a bias of studying differing age groups in monoinfection studies. Combined, these infections lead to difficulties in conducting and interpreting human coinfection studies.

RECENT FINDINGS

Interactions between the two parasites may affect morbidity associated with either infection; both by influencing mechanisms directly associated with the development of those morbidities and by influencing mechanisms associated with resistance or susceptibility to the other infection. However, conflicting results are reported due to inherent difficulties in studying coinfections. More studies with stringent designs are required to clarify interactions between the two parasites. Recent monoinfection studies indicate that further coinfection studies may need to have a wider age range than previously studied. These studies also need to harness new techniques, both for data collection and analysis that are being developed for modern epidemiological studies. These techniques will allow an essential multidisciplinary approach to be taken.

SUMMARY

Coinfection with Plasmodium and schistosome infection has implications for the health of children of all ages in sub-Saharan Africa. It is important to gain further understanding of the interactions between the two parasites in all age groups.

Proportions of CD4+ memory T cells are altered in individuals chronically infected with Schistosoma haematobium

Characterisation of protective helminth acquired immunity in humans or experimental models has focused on effector responses with little work conducted on memory responses. Here we show for the first time, that human helminth infection is associated with altered proportions of the CD4+ memory T cells, with an associated alteration of T_H1 responses. The reduced CD4+ memory T cell proportions are associated with a significantly lower ratio of schistosome-specific IgE/IgG4 (marker for resistance to infection/re-infection) in uninfected older people. Helminth infection does not affect the CD8+ memory T cell pool. Furthermore, we show for the first time in a helminth infection that the CD4+ memory T cell proportions decline following curative anti-helminthic treatment despite increased CD4+ memory cell replication. Reduced accumulation of the CD4+ memory T cells in schistosome-infected people has implications for the development of natural or vaccine induced schistosome-specific protective immunity as well as for unrelated pathogens.

Atopy is inversely related to schistosome infection intensity: a comparative study in Zimbabwean villages with distinct levels of Schistosoma haematobium infection

Background

The hygiene hypothesis suggests that parasitic infections protect against allergic diseases by modulating the host's immune responses. Experimental studies indicate that this protection depends on the intensity of parasitic infection, but this observation has not been tested in human populations. The aim of this study is to investigate whether the intensity of Schistosoma haematobium infection is related to atopic responses and whether this relationship differs between populations with distinct parasite transmission dynamics.

Methods

The study was conducted in two villages with different Schistosoma haematobium transmission dynamics, i.e. high (n = 365) and low (n = 307) transmission. Allergic reactivity to the common house dust mite (Dermatophagoides pteronyssinus) was measured by skin prick tests and allergen-specific IgE and IgG4 quantified by enzyme-linked immunosorbent assay. Atopic responses were related to current infection intensity and schistosome transmission levels.

Results

Schistosome infection intensity was negatively associated with the skin prick reactivity, mite-specific IgE and the ratio IgE/IgG4 in the high-transmission village. However, when only low levels of infection were analyzed in the 2 villages, there was no correlation between mite-specific responses and infection intensity.

Conclusion

The relationship between schistosome infection and atopic responses is dependent on the intensity of current schistosome infection. Thus, consistent with results from animal models, with an increasing parasite burden, the immunoregulation of immune responses to allergens appears to become more pronounced.

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.

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.

Schistosoma haematobium infection affects Plasmodium falciparum-specific IgG responses associated with protection against malaria

We have previously shown that antibody responses directed to Plasmodium falciparum merozoite surface protein (MSP)-1, MSP-2 and glutamate-rich protein (GLURP) are associated with anti-malarial protection in residents of the Niakhar area of Senegal. In the same area, urinary schistosomiasis is frequent and we therefore assessed the possible influence of Schistosoma haematobium infection on these protective anti-malarial IgG responses. After adjustment for confounders, we found that the levels of IgG1 directed to MSP1 and GLURP were significantly lower in helminth carriers. The higher circulating levels of interleukin (IL)-10 present in the plasma of co-infected individuals were associated with decreased anti-plasmodial IgG responses, particularly of those directed to MSP-2. Our data thus reveal a modulation of P. falciparum-specific immune responses in the presence of a trematode helminth infection, potentially increasing infected individuals' risk of plasmodial infection or disease.

Circulating cytokine levels and antibody responses to human Schistosoma haematobium: IL-5 and IL-10 levels depend upon age and infection status

Experimental schistosome infections induce strong parasite-specific Th2 responses. This study aims to relate human systemic cytokine and antibody levels to schistosome infection levels and history. Levels of anti-Schistosoma haematobium antibodies (directed against crude cercariae, egg and adult worm antigens) and plasma cytokines (IFN-γ, IL-2, IL-4, IL-5, IL-10, IL-13, IL-17, IL-21, and IL-23) were measured by ELISA in 227 Zimbabweans (6–60 years old) in a schistosome-endemic area and related to age and infection status. Egg-positive people had significantly higher levels of specific antibodies, IL-2, IFN-γ and IL-23. In contrast, egg-negative individuals had significantly higher circulating IL-10, IL-4, IL-13 and IL-21 that were detected with high frequency in all participants. Subjects with detectable plasma IL-17 produced few or no eggs. When analyzed by age, IL-4 and IL-10 increased significantly, as did schistosome-specific antibodies. However, when age was combined with infection status, IL-5 declined over time in egg-positive people, while increased with age in the egg-negative group. Older, lifelong residents had significantly higher IL-4 and IL-5 levels than younger egg-negative people. Thus, a mixed Th1/Th2 systemic environment occurs in people with patent schistosome infection, while a stronger Th2-dominated suite of cytokines is evident in egg-negative individuals.

Regulatory and activated T cells in human Schistosoma haematobium infections

Acquired immunity against helminths is characterised by a complex interplay between the effector Th1 and Th2 immune responses and it slowly manifests with age as a result of cumulative exposure to parasite antigens. Data from experimental models suggest that immunity is also influenced by regulatory T cells (Treg), but as yet studies on Treg in human schistosome infections are limited. This study investigated the relationship between schistosome infection intensity and the two cell populations regulatory T cells (TREG: CD4(+(dim))CD25(+(high))FOXP3(+)CD127(low)), and activated (Tact: CD4(+)CD25(+)FOXP3(-)) T cells in Zimbabweans exposed to Schistosoma haematobium parasites. Participants were partitioned into two age groups, young children (8-13 years) in whom schistosome infection levels were rising to peak and older people (14+ years) with declining infection levels. The relationship between Tact proportions and schistosome infection intensity remained unchanged with age. However Treg proportions rose significantly with increasing infection in the younger age group. In contrast Treg were negatively correlated to infection intensity in the older age group. The relative proportions of regulatory T cells differ significantly between young individuals in whom high infection is associated with an enhanced regulatory phenotype and older infected patients in whom the regulatory response is attenuated. This may influence or reflect different stages of the development of protective schistosome acquired immunity and immunopathogenesis.

Patent filarial infection modulates malaria-specific type 1 cytokine responses in an IL-10-dependent manner in a filaria/malaria-coinfected population

The effect of filarial infections on malaria-specific immune responses was investigated in Malian villages coendemic for filariasis (Fil) and malaria. Cytokines were measured from plasma and Ag-stimulated whole blood from individuals with Wuchereria bancrofti and/or Mansonella perstans infections (Fil(+); n = 19) and those without evidence of filarial infection (Fil(-); n = 19). Plasma levels of IL-10 (geometric mean [GM], 22.8 vs 10.4) were higher in Fil(+) compared with Fil(-), whereas levels of IFN-inducible protein (IP)-10 were lower in Fil(+) (GM, 66.3 vs 110.0). Fil(+) had higher levels of spontaneously secreted IL-10 (GM, 59.3 vs 6.8 pg/ml) and lower levels of IL-2 (1.0 vs 1.2 pg/ml) than did Fil(-). Although there were no differences in levels of Staphylococcus aureus enterotoxin B-induced cytokines between the two groups, Fil(+) mounted lower IL-12p70 (GM, 1.11 vs 3.83 pg/ml; p = 0.007), IFN-gamma (GM, 5.44 vs 23.41 pg/ml; p = 0.009), and IP-10 (GM, 29.43 vs 281.7 pg/ml; p = 0.007) responses following malaria Ag (MalAg) stimulation compared with Fil(-). In contrast, Fil(+) individuals had a higher MalAg-specific IL-10 response (GM, 7318 pg/ml vs 3029 pg/ml; p = 0.006) compared with those without filarial infection. Neutralizing Ab to IL-10 (but not to TGFbeta) reversed the down-regulated MalAg-specific IFN-gamma and IP-10 (p < 0.001) responses in Fil(+). Together, these data demonstrate that filarial infections modulate the Plasmodium falciparum-specific IL-12p70/IFN-gamma secretion pathways known to play a key role in resistance to malaria and that they do so in an IL-10-dependent manner.