A planetary health innovation for disease, food and water challenges in Africa

Many communities in low- and middle-income countries globally lack sustainable, cost-effective and mutually beneficial solutions for infectious disease, food, water and poverty challenges, despite their inherent interdependence^1-7. Here we provide support for the hypothesis that agricultural development and fertilizer use in West Africa increase the burden of the parasitic disease schistosomiasis by fuelling the growth of submerged aquatic vegetation that chokes out water access points and serves as habitat for freshwater snails that transmit Schistosoma parasites to more than 200 million people globally^8-10. In a cluster randomized controlled trial (ClinicalTrials.gov: NCT03187366) in which we removed invasive submerged vegetation from water points at 8 of 16 villages (that is, clusters), control sites had 1.46 times higher intestinal Schistosoma infection rates in schoolchildren and lower open water access than removal sites. Vegetation removal did not have any detectable long-term adverse effects on local water quality or freshwater biodiversity. In feeding trials, the removed vegetation was as effective as traditional livestock feed but 41 to 179 times cheaper and converting the vegetation to compost provided private crop production and total (public health plus crop production benefits) benefit-to-cost ratios as high as 4.0 and 8.8, respectively. Thus, the approach yielded an economic incentive-with important public health co-benefits-to maintain cleared waterways and return nutrients captured in aquatic plants back to agriculture with promise of breaking poverty-disease traps. To facilitate targeting and scaling of the intervention, we lay the foundation for using remote sensing technology to detect snail habitats. By offering a rare, profitable, win-win approach to addressing food and water access, poverty alleviation, infectious disease control and environmental sustainability, we hope to inspire the interdisciplinary search for planetary health solutions¹¹ to the many and formidable, co-dependent global grand challenges of the twenty-first century.

Exposure, hazard, and vulnerability all contribute to Schistosoma haematobium re-infection in northern Senegal

Background

Infectious disease risk is driven by three interrelated components: exposure, hazard, and vulnerability. For schistosomiasis, exposure occurs through contact with water, which is often tied to daily activities. Water contact, however, does not imply risk unless the environmental hazard of snails and parasites is also present in the water. By increasing reliance on hazardous activities and environments, socio-economic vulnerability can hinder reductions in exposure to a hazard. We aimed to quantify the contributions of exposure, hazard, and vulnerability to the presence and intensity of Schistosoma haematobium re-infection.

Methodology/Principal findings

In 13 villages along the Senegal River, we collected parasitological data from 821 school-aged children, survey data from 411 households where those children resided, and ecological data from all 24 village water access sites. We fit mixed-effects logistic and negative binomial regressions with indices of exposure, hazard, and vulnerability as explanatory variables of Schistosoma haematobium presence and intensity, respectively, controlling for demographic variables. Using multi-model inference to calculate the relative importance of each component of risk, we found that hazard (Ʃw_{i =} 0.95) was the most important component of S. haematobium presence, followed by vulnerability (Ʃw_i = 0.91). Exposure (Ʃw_i = 1.00) was the most important component of S. haematobium intensity, followed by hazard (Ʃw_i = 0.77). Model averaging quantified associations between each infection outcome and indices of exposure, hazard, and vulnerability, revealing a positive association between hazard and infection presence (OR = 1.49, 95% CI 1.12, 1.97), and a positive association between exposure and infection intensity (RR 2.59–3.86, depending on the category; all 95% CIs above 1)

Conclusions/Significance

Our findings underscore the linkages between social (exposure and vulnerability) and environmental (hazard) processes in the acquisition and accumulation of S. haematobium infection. This approach highlights the importance of implementing both social and environmental interventions to complement mass drug administration.

While the impacts of natural hazards tend to be described in terms of social determinants such as exposure and vulnerability, the risk for infectious disease is often expressed in terms of environmental determinants without fully considering the socio-ecological processes that put people in contact with infective agents of disease. In the case of schistosomiasis, risk is determined by human interactions with freshwater environments where schistosome parasites circulate between people and aquatic snails. In this study, we quantified the relative contributions of exposure, hazard, and vulnerability to schistosome re-infection among schoolchildren in an endemic region of northern Senegal. We find that hazard and vulnerability influence whether a child becomes infected, while exposure and hazard influence the burden of worms once infection is acquired. Increasing numbers of worms is known to be positively associated with increasing severity of disease. Our findings underscore the importance of evaluating social and environmental determinants of disease simultaneously; omitting measures of exposure, hazard or vulnerability may limit our understanding of risk.

Schistosome infection in Senegal is associated with different spatial extents of risk and ecological drivers for Schistosoma haematobium and S. mansoni

Schistosome parasites infect more than 200 million people annually, mostly in sub-Saharan Africa, where people may be co-infected with more than one species of the parasite. Infection risk for any single species is determined, in part, by the distribution of its obligate intermediate host snail. As the World Health Organization reprioritizes snail control to reduce the global burden of schistosomiasis, there is renewed importance in knowing when and where to target those efforts, which could vary by schistosome species. This study estimates factors associated with schistosomiasis risk in 16 villages located in the Senegal River Basin, a region hyperendemic for Schistosoma haematobium and S. mansoni. We first analyzed the spatial distributions of the two schistosomes’ intermediate host snails (Bulinus spp. and Biomphalaria pfeifferi, respectively) at village water access sites. Then, we separately evaluated the relationships between human S. haematobium and S. mansoni infections and (i) the area of remotely-sensed snail habitat across spatial extents ranging from 1 to 120 m from shorelines, and (ii) water access site size and shape characteristics. We compared the influence of snail habitat across spatial extents because, while snail sampling is traditionally done near shorelines, we hypothesized that snails further from shore also contribute to infection risk. We found that, controlling for demographic variables, human risk for S. haematobium infection was positively correlated with snail habitat when snail habitat was measured over a much greater radius from shore (45 m to 120 m) than usual. S. haematobium risk was also associated with large, open water access sites. However, S. mansoni infection risk was associated with small, sheltered water access sites, and was not positively correlated with snail habitat at any spatial sampling radius. Our findings highlight the need to consider different ecological and environmental factors driving the transmission of each schistosome species in co-endemic landscapes.

Schistosome parasites infect more than 200 million people worldwide, mainly in sub-Saharan Africa, where many people are at-risk for infection by multiple schistosome species simultaneously. To reduce the global burden of schistosomiasis, control of the parasites’ intermediate host–specific species of freshwater snails–has been elevated in priority to complement mass drug administration campaigns in endemic areas. To maximize the efficacy and efficiency of snail control efforts, a better understanding of where to target intermediate host snails is badly needed. This includes a better understanding of the spatial scale at which snails in the environment contribute to human infection risk, and, in co-endemic settings, how ecological determinants of infection risk vary by schistosome species. We used quantitative snail sampling and remotely-sensed data at 16 villages in the Senegal River Basin to compare and contrast ecological correlates and spatial scales of infection risk from freshwater snails that transmit Schistosoma haematobium versus S. mansoni. We found that infection risk for S. haematobium was associated with snail habitat at a larger spatial radius than is typically considered for schistosomiasis monitoring and control, whereas infection risk for S. mansoni was not positively correlated with snail habitat at any spatial sampling radius, but was associated with small water access sites enclosed by emergent vegetation. Our findings highlight the need to consider the different ecological and environmental factors driving the transmission of each schistosome species in co-endemic landscapes.

Land use impacts on parasitic infection: a cross-sectional epidemiological study on the role of irrigated agriculture in schistosome infection in a dammed landscape

Background

Water resources development promotes agricultural expansion and food security. But are these benefits offset by increased infectious disease risk? Dam construction on the Senegal River in 1986 was followed by agricultural expansion and increased transmission of human schistosomes. Yet the mechanisms linking these two processes at the individual and household levels remain unclear. We investigated the association between household land use and schistosome infection in children.

Methods

We analyzed cross-sectional household survey data (n = 655) collected in 16 rural villages in August 2016  across demographic, socio-economic and land use dimensions, which were matched to Schistosoma haematobium (n = 1232) and S. mansoni (n = 1222) infection data collected from school-aged children. Mixed effects regression determined the relationship between irrigated area and schistosome infection presence and intensity.

Results

Controlling for socio-economic and demographic risk factors, irrigated area cultivated by a household was associated with an increase in the presence of S. haematobium infection (odds ratio [OR] = 1.14; 95% confidence interval [95% CI]: 1.03–1.28) but not S. mansoni infection (OR = 1.02; 95% CI: 0.93–1.11). Associations between infection intensity and irrigated area were positive but imprecise (S. haematobium: rate ratio [RR] = 1.05; 95% CI: 0.98–1.13, S. mansoni: RR = 1.09; 95% CI: 0.89–1.32).

Conclusions

Household engagement in irrigated agriculture increases individual risk of S. haematobium but not S. mansoni infection. Increased contact with irrigated landscapes likely drives exposure, with greater impacts on households relying on agricultural livelihoods.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-021-00816-5.

Prevalence and Subtype Distribution of Blastocystis sp. in Senegalese School Children

Blastocystis sp. is an enteric protozoan that frequently colonizes humans and many animals. Despite impacting on human health, data on the prevalence and subtype (ST) distribution of Blastocystis sp. remain sparse in Africa. Accordingly, we performed the first multicenter and largest epidemiological survey ever conducted on Blastocystis sp. for this continent. A total of 731 stool samples collected from healthy school children living in 10 villages of the northwestern region of Senegal were tested for the presence of Blastocystis sp. by real-time polymerase chain reaction followed by subtyping of positive samples. Considerable variation in prevalence between villages (51.7 to 100%) was evident with the overall prevalence being 80.4%. Mixed infections were identified in 23% of positive individuals. Among 453 school children with a single infection, ST2 was predominant, followed by ST1, ST3, ST7, ST10, and ST14; this is the first report of ST10 and ST14 in humans. Genetic polymorphisms were evident at the intra-ST level with the identification of numerous ST1 to ST3 genotypes. ST1 showed the greatest intra-ST diversity followed by ST2 and ST3. The prevalence and distribution of STs and genotypes varied among target villages, pointing to several potential infection sources, including human-to-human, zoonotic, and waterborne transmission.

Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission

Recently, the World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites. We sought to identify robust indicators that would enable precision targeting of these snails. At the site of the world's largest recorded schistosomiasis epidemic-the Lower Senegal River Basin in Senegal-intensive sampling revealed positive relationships between intermediate host snails (abundance, density, and prevalence) and human urogenital schistosomiasis reinfection (prevalence and intensity in schoolchildren after drug administration). However, we also found that snail distributions were so patchy in space and time that obtaining useful data required effort that exceeds what is feasible in standard monitoring and control campaigns. Instead, we identified several environmental proxies that were more effective than snail variables for predicting human infection: the area covered by suitable snail habitat (i.e., floating, nonemergent vegetation), the percent cover by suitable snail habitat, and size of the water contact area. Unlike snail surveys, which require hundreds of person-hours per site to conduct, habitat coverage and site area can be quickly estimated with drone or satellite imagery. This, in turn, makes possible large-scale, high-resolution estimation of human urogenital schistosomiasis risk to support targeting of both mass drug administration and snail control efforts.

Safety and efficacy of the rSh28GST urinary schistosomiasis vaccine: A phase 3 randomized, controlled trial in Senegalese children

Background

Urinary schistosomiasis, the result of infection by Schistosoma haematobium (Sh), remains a major global health concern. A schistosome vaccine could represent a breakthrough in schistosomiasis control strategies, which are presently based on treatment with praziquantel (PZQ). We report the safety and efficacy of the vaccine candidate recombinant 28-kDa glutathione S-transferase of Sh (rSh28GST) designated as Bilhvax, in a phase 3 trial conducted in Senegal.

Methods and findings

After clearance of their ongoing schistosomiasis infection with two doses of PZQ, 250 children aged 6–9 years were randomized to receive three subcutaneous injections of either rSh28GST/Alhydrogel (Bilhvax group) or Alhydrogel alone (control group) at week 0 (W0), W4, and W8 and then a booster at W52 (one year after the first injection). PZQ treatment was given at W44, according to previous phase 2 results. The primary endpoint of the analysis was efficacy, evaluated as a delay of recurrence of urinary schistosomiasis, defined by a microhematuria associated with at least one living Sh egg in urine from baseline to W152. During the 152-week follow-up period, there was no difference between study arms in the incidence of serious adverse events. The median follow-up time for subjects without recurrence was 22.9 months for the Bilhvax group and 18.8 months for the control group (log-rank p = 0.27). At W152, 108 children had experienced at least one recurrence in the Bilhvax group versus 112 in the control group. Specific immunoglobulin (Ig)G1, IgG2, and IgG4, but not IgG3 or IgA titers, were increased in the vaccine group.

Conclusions

While Bilhvax was immunogenic and well tolerated by infected children, a sufficient efficacy was not reached. The lack of effect may be the result of several factors, including interference by individual PZQ treatments administered each time a child was found infected, or the chosen vaccine-injection regimen favoring blocking IgG4 rather than protective IgG3 antibodies. These observations contrasting with results obtained in experimental models will help in the design of future trials.

Trial registration

ClinicalTrials.gov NCT 00870649

Vaccines represent an attractive tool in the fight against schistosomiasis. Pre-clinical immunization studies with the schistosome enzyme 28 kDa glutathione S-transferase (28GST) have shown a significant reduction of schistosome egg production and subsequent pathology. The objective of the present phase 3 trial was to assess the efficacy and safety of vaccination with the recombinant 28GST of Schistosoma haematobium (rSh28GST) named Bilhvax, in infected school children. After Praziquantel treatment before inclusion and three administrations of rSh28GST at one month interval as primo-vaccination, subjects received a boost injection one year after the first administration. The efficacy was evaluated as a delay of recurrence of urinary schistosomiasis. While immunological analysis showed that Bilhvax induced a consistent immune response characterized by antibodies able to inhibit 28GST enzymatic activity, the efficacy endpoint was not reached. This lack of significant effect may be due to the negative conjunction of a too challenging recurrence criterion associated with safety measures ensuring repeated PZQ treatment. The control of these main factors will be essential for the subsequent trials and must provide evidence of the Bilhvax efficacy as a safe vaccine against uro-genital schistosomiasis.

Sex-dependent interactions between leptin, wasting and humoral immunity in two ethnic communities of school-aged children differentially exposed to Schistosoma haematobium

Background

Leptin is a nutritional hormone whose production is generally higher in females. We investigated how leptin is associated with sex dimorphism during urinary schistosomiasis in relation with wasting.

Methods

A cross-sectional study was carried out in three villages in northern Senegal. Ninety-eight school-aged children belonging to the Fulani or Wolof villages were enrolled. We performed parasitic diagnosis and anthropometric measurement to evaluate nutritional status. We collected peripheral blood to determine the amount of circulating leptin and immunoglobulin G (IgG), IgG4 and IgE directed to soluble worm antigen preparation (SWAP).

Results

The prevalence of Schistosoma haematobium infection was higher among boys regardless of ethnic group, but exposure to parasites did not exacerbate malnutrition. The greater ability of girls to produce leptin was not altered by schistosomiasis and was recovered in both ethnic groups. However, while the usual correlation between leptin and fat storage was preserved in Fulani girls, it was disrupted in Fulani boys, who displayed a remarkable susceptibility for wasting. Finally, we observed that leptin was negatively associated with the level of antibodies in Wolof boys.

Conclusions

Leptin can be disconnected from body fat and may exert a sex-dependent influence on host immune response to S. haematobium infection in Senegalese children.

Effects of malnutrition on children's immunity to bacterial antigens in Northern Senegal

To evaluate immunity to vaccine-preventable diseases according to nutritional status, a longitudinal study was conducted in Senegalese children ages 1-9 years old. A linear regression analysis predicted that weight for age was positively associated with immunoglobulin G (IgG) response to tetanus toxoid in children born during the rainy season or at the beginning of the dry season. A relationship between village, time of visits, and levels of antibodies to tetanus showed that environmental factors played a role in modulating humoral immunity to tetanus vaccine over time. Moreover, a whole-blood stimulation assay highlighted that the production of interferon-γ (IFN-γ) in response to tetanus toxoid was compromised in stunted children. However, the absence of cytokine modulation in response to Mycobacterium tuberculosis-purified protein derivatives and phytohemagglutinin suggests that the overall ability to produce IFN-γ was preserved in stunted children. Therefore, these results show that nutritional status can specifically alter the efficacy of long-lasting immunity to tetanus.

Plasmodium falciparum infection during dry season: IgG responses to Anopheles gambiae salivary gSG6-P1 peptide as sensitive biomarker for malaria risk in Northern Senegal

BACKGROUND

The Northern part of Senegal is characterized by a low and seasonal transmission of malaria. However, some Plasmodium falciparum infections and malaria clinical cases are reported during the dry season. This study aims to assess the relationship between IgG antibody (Ab) responses to gSG6-P1 mosquito salivary peptide and the prevalence of P. falciparum infection in children during the dry season in the Senegal River Valley. The positive association of the Ab response to gSG6-P1, as biomarker of human exposure to Anopheles vector bite, and P. falciparum infectious status (uninfected, infected-asymptomatic or infected-symptomatic) will allow considering this biomarker as a potential indicator of P. falciparum infection risk during the dry season.

METHODS

Microscopic examination of thick blood smears was performed in 371 and 310 children at the start (January) and at the end (June) of the dry season, respectively, in order to assess the prevalence of P. falciparum infection. Collected sera were used to evaluate IgG response to gSG6-P1 by ELISA. Association between parasitological and clinical data (infected-asymptomatic or infected-symptomatic) and the anti-gSG6-P1 IgG levels were evaluated during this period.

RESULTS

The prevalence of P. falciparum infection was very low to moderate according to the studied period and was higher in January (23.5%) compared to June (3.5%). Specific IgG response was also different between uninfected children and asymptomatic carriers of the parasite. Children with P. falciparum infection in the dry season showed higher IgG Ab levels to gSG6-P1 than uninfected children.

CONCLUSIONS

The results strengthen the hypothesis that malaria transmission is maintained during the dry season in an area of low and seasonal transmission. The measurement of IgG responses to gSG6-P1 salivary peptide could be a pertinent indicator of human malaria reservoir or infection risk in this particular epidemiological context. This promising immunological marker could be useful for the evaluation of the risk of P. falciparum exposure observed during dry season and, by consequences, could be used for the survey of potential pre-elimination situation.

gSG6-P1 salivary biomarker discriminates micro-geographical heterogeneity of human exposure to Anopheles bites in low and seasonal malaria areas

BACKGROUND

Over the past decade, a sharp decline of malaria burden has been observed in several countries. Consequently, the conventional entomological methods have become insufficiently sensitive and probably under-estimate micro-geographical heterogeneity of exposure and subsequent risk of malaria transmission. In this study, we investigated whether the human antibody (Ab) response to Anopheles salivary gSG6-P1 peptide, known as a biomarker of Anopheles exposure, could be a sensitive and reliable tool for discriminating human exposure to Anopheles bites in area of low and seasonal malaria transmission.

METHODS

A multi-disciplinary survey was performed in Northern Senegal where An. gambiae s.l. is the main malaria vector. Human IgG Ab response to gSG6-P1 salivary peptide was compared according to the season and villages in children from five villages in the middle Senegal River valley, known as a low malaria transmission area.

RESULTS

IgG levels to gSG6-P1 varied considerably according to the villages, discriminating the heterogeneity of Anopheles exposure between villages. Significant increase of IgG levels to gSG6-P1 was observed during the peak of exposure to Anopheles bites, and decreased immediately after the end of the exposure season. In addition, differences in the season-dependent specific IgG levels between villages were observed after the implementation of Long-Lasting Insecticidal Nets by The National Malaria Control Program in this area.

CONCLUSION

The gSG6-P1 salivary peptide seems to be a reliable tool to discriminate the micro-geographical heterogeneity of human exposure to Anopheles bites in areas of very low and seasonal malaria transmission. A biomarker such as this could also be used to monitor and evaluate the possible heterogeneous effectiveness of operational vector control programs in low-exposure areas.

Seroprevalence of pertussis in Senegal: a prospective study

BACKGROUND

Pertussis, also known as whooping cough, is a vaccine-preventable respiratory disease caused by Bordetella pertussis infection, against which Senegalese children are immunized with the diphtheria-tetanus-whole cell pertussis vaccine (DTwP). Seroepidemiology of pertussis has been widely described in industrialized countries, but rare are the studies referring to it in developing countries.

METHODS

We conducted a longitudinal survey in Northern Senegal to investigate the epidemiology of B. pertussis by evaluating the IgG antibody (Ab) response against pertussis toxin (PT). A cohort of 410 children aged 1 to 9 from five villages in the Middle Senegal River Valley were followed-up for 18 months. During that period, five visits were made to assess the immunological status of the children.

PRINCIPAL FINDINGS

PT-specific IgG responses were significantly different according to age. Until the age of 3, there was a decrease in the Ab response, which then increased in the older groups. Assessment of IgG antibodies to PT (IgG-PT) suggested evidence of recent exposures to the pathogen. Surprisingly, in one of the five villages the average Ab response to PT was very low at all ages during the first 6 months of the study. At the third visit, IgG-PT concentrations peaked to very high levels, to slightly decline at the end of the survey. This indicates an outbreak of B. pertussis, whereas in the other villages a pertussis endemic profile could be observed.

CONCLUSIONS

Pertussis is endemic in Northern Senegal despite the introduction of vaccination. The circulation of the bacteria seems to differ between geographic locations and over time. A more complete understanding of the epidemiology of pertussis and its environmental determinants could provide information to adapt vaccination programs.

Safety and immunogenicity of rSh28GST antigen in humans: phase 1 randomized clinical study of a vaccine candidate against urinary schistosomiasis

BACKGROUND

Treatment of urinary schistosomiasis by chemotherapy remains challenging due to rapid re-infection and possibly to limited susceptibility to praziquantel treatment. Therefore, therapeutic vaccines represent an attractive alternative control strategy. The objectives of this study were to assess the safety and tolerability profile of the recombinant 28 kDa glutathione S-transferase of Schistosoma haematobium (rSh28GST) in healthy volunteers, and to determine its immunogenicity.

METHODOLOGY

Volunteers randomly received 100 µg rSh28GST together with aluminium hydroxide (Alum) as adjuvant (n = 8), or Alum alone as a comparator (n = 8), twice with a 28-day interval between doses. A third dose of rSh28GST or Alum alone was administered to this group at day 150. In view of the results obtained, another group of healthy volunteers (n = 8) received two doses of 300 µg of rSh28GST, again with a 28-day interval. A six-month follow-up was performed with both clinical and biological evaluations. Immunogenicity of the vaccine candidate was evaluated in terms of specific antibody production, the capacity of sera to inhibit enzymatic activity of the antigen, and in vitro cytokine production.

PRINCIPAL FINDINGS

Among the 24 healthy male participants no serious adverse events were reported in the days or weeks after administration. Four subjects under rSh28GST reported mild reactions at the injection site while a clinically insignificant increase in bilirubin was observed in 8/24 subjects. No hematological nor biochemical evidence of toxicity was detected. Immunological analysis showed that rSh28GST was immunogenic. The induced Th2-type response was characterized by antibodies capable of inhibiting the enzymatic activity of rSh28GST.

CONCLUSIONS

rSh28GST in Alum did not induce any significant toxicity in healthy adults and generated a Th2-type immune response. Together with previous preclinical results, the data of safety, tolerability and quality of the specific immune response provide evidence that clinical trials with rSh28GST could be continued in humans as a potential vaccine candidate against urinary schistosomiasis.

Differential acquisition of human antibody responses to Plasmodium falciparum according to intensity of exposure to Anopheles bites

Malaria immunity is modulated by many environmental and epidemiological factors. This study evaluates the influence of a hitherto unstudied environmental-epidemiological factor, namely the impact of human exposure to Anopheles bites on the isotype profile of acquired antibody responses to Plasmodium falciparum. In two Senegalese villages where the intensity of exposure to Anopheles bites was markedly different (high and low exposure), specific IgG1 and IgG3 responses to P. falciparum whole schizont extract (WSE) and circumsporozoite protein (CSP) were evaluated at the peak of Anopheles exposure (September) and later (December) in a cohort of 120 children aged 3-8 years. Multivariate analysis showed a significantly lower IgG1 response against P. falciparum WSE and CSP in children highly exposed to Anopheles bites (Gankette) compared to those who were weakly exposed (Mboula). In contrast, in both villages, parasitemia and increasing age were strongly associated with higher IgG1 and IgG3 levels. We hypothesize that high exposure to Anopheles bites could inhibit IgG1-dependent responsiveness to P. falciparum known to induce protective immune responses against malaria. The impact of mosquito saliva on the regulation of specific protective immunity may need to be taken into account in epidemiological studies and trials for malaria vaccines.

Immunological consequences of intermittent preventive treatment against malaria in Senegalese preschool children

BACKGROUND

Intermittent preventive treatment in children (IPTc) is a promising strategy to control malaria morbidity. A significant concern is whether IPTc increases children's susceptibility to subsequent malaria infection by altering their anti-Plasmodium acquired immunity.

METHODS

To investigate this concern, IgG antibody (Ab) responses to Plasmodium falciparum schizont extract were measured in Senegalese children (6 months-5 years old) who had received three rounds of IPTc with artesunate + sulphadoxine-pyrimethamine (or placebo) at monthly intervals eight months earlier. Potential confounding factors, such as asexual malaria parasitaemia and nutritional status were also evaluated.

RESULTS

Firstly, a bivariate analysis showed that children who had received IPTc had lower anti-Plasmodium IgG Ab levels than the non-treated controls. When epidemiological parameters were incorporated into a multivariate regression, gender, nutritional status and haemoglobin concentration did not have any significant influence. In contrast, parasitaemia, past malaria morbidity and increasing age were strongly associated with a higher specific IgG response.

CONCLUSIONS

The intensity of the contacts with P. falciparum seems to represent the main factor influencing anti-schizont IgG responses. Previous IPTc does not seem to interfere with this parasite-dependent acquired humoral response eight months after the last drug administration.

Schistosomiasis coinfection in children influences acquired immune response against Plasmodium falciparum malaria antigens

Background

Malaria and schistosomiasis coinfection frequently occurs in tropical countries. This study evaluates the influence of Schistosoma haematobium infection on specific antibody responses and cytokine production to recombinant merozoite surface protein-1-19 (MSP1-₁₉) and schizont extract of Plasmodium falciparum in malaria-infected children.

Methodology

Specific IgG1 to MSP1-₁₉, as well as IgG1 and IgG3 to schizont extract were significantly increased in coinfected children compared to P. falciparum mono-infected children. Stimulation with MSP1-₁₉ lead to a specific production of both interleukin-10 (IL-10) and interferon-γ (IFN-γ), whereas the stimulation with schizont extract produced an IL-10 response only in the coinfected group.

Conclusions

Our study suggests that schistosomiasis coinfection favours anti-malarial protective antibody responses, which could be associated with the regulation of IL-10 and IFN-γ production and seems to be antigen-dependent. This study demonstrates the importance of infectious status of the population in the evaluation of acquired immunity against malaria and highlights the consequences of a multiple infection environment during clinical trials of anti-malaria vaccine candidates.

Evaluation of antibody response to Plasmodium falciparum in children according to exposure of Anopheles gambiae s.l or Anopheles funestus vectors

Background

In sub-Saharan areas, malaria transmission was mainly ensured by Anopheles. gambiae s.l. and Anopheles. funestus vectors. The immune response status to Plasmodium falciparum was evaluated in children living in two villages where malaria transmission was ensured by dissimilar species of Anopheles vectors (An. funestus vs An. gambiae s.l.).

Methods

A multi-disciplinary study was performed in villages located in Northern Senegal. Two villages were selected: Mboula village where transmission is strictly ensured by An. gambiae s.l. and Gankette Balla village which is exposed to several Anopheles species but where An. funestus is the only infected vector found. In each village, a cohort of 150 children aged from one to nine years was followed during one year and IgG response directed to schizont extract was determined by ELISA.

Results

Similar results of specific IgG responses according to age and P. falciparum infection were observed in both villages. Specific IgG response increased progressively from one-year to 5-year old children and then stayed high in children from five to nine years old. The children with P. falciparum infection had higher specific antibody responses compared to negative infection children, suggesting a strong relationship between production of specific antibodies and malaria transmission, rather than protective immunity. In contrast, higher variation of antibody levels according to malaria transmission periods were found in Mboula compared to Gankette Balla. In Mboula, the peak of malaria transmission was followed by a considerable increase in antibody levels, whereas low and constant anti-malaria IgG response was observed throughout the year in Gankette Balla.

Conclusion

This study shows that the development of anti-malaria antibody response was profoundly different according to areas where malaria exposure is dependent with different Anopheles species. These results are discussed according to i) the use of immunological tool for the evaluation of malaria transmission and ii) the influence of Anopheles vectors species on the regulation of antibody responses to P. falciparum.

Schistosomiasis co-infection in humans influences inflammatory markers in uncomplicated Plasmodium falciparum malaria

Malaria and schistosomiasis are the two major parasite diseases present in developing countries. The epidemiological co-infection with schistosomiasis could influence the development of the physiological reaction associated with Plasmodium falciparum infection in human. Most studies have demonstrated the association of circulating levels of interferon-gamma (IFN-gamma), tumour necrosis factor-a (TNF-alpha), interleukin-10 (IL-10), transforming growth factor (TGF-beta) and soluble Tumour Necrosis Factor Receptors (sTNF-RI and sTNF-RII) with the morbidity of malaria. In the present study, we showed that Schistosoma haematobium co-infection influences, in an age-dependent manner, the unbalance between pro- and anti-inflammatory circulating cytokines that play a key role during malaria infection. Indeed, children co-infected by S. haematobium have higher levels of IFN-gamma and sTNF-RII than children infected only by P. falciparum. In contrast, co-infected adults presented a significant increase of IFN-gamma, IL-10, TGF-beta, sTNF-RI and sTNF-RII rates and IL-10/TNF-alpha ratio. Taken together, this study indicates that schistosomiasis co-infection can unbalance the regulation of inflammatory factors in uncomplicated P. falciparum malaria. The possible consequences of the schistosomiasis co-infection for age-dependent malaria morbidity are discussed.

Specific isotype immune response in the diagnosis of human schistosomiasis pathology?

Since the few indirect markers available for assessing the development and the stage of intestinal schistosomiasis morbidity are weakly specific, endoscopy is still the only method able to detect severe forms of pathology. Therefore, we evaluated the isotype antibody response to the current schistosome antigen preparation (soluble egg antigens [SEA]) in 142 Senegalese patients infected with Schistosoma mansoni. They were stratified into three different stages of pathology according to ultrasonographic, endoscopic, and clinical parameters (stage 1 = no detectable pathology; stage 2 = moderate morbidity; stage 3 = severe forms of pathology). Only median specific IgG4, IgE, and IgA responses changed according to the stage of pathology. The IgA level was significantly higher in stages 2 and 3 compared with stage 1, and the IgE level was higher in stage 3 compared with stage 1. A high specific IgG4 level was observed only in stage 3 and was significantly different compared with stage 2. We show an association between the variability of the specific response to SEA and the degree of morbidity, and demonstrate that IgA and IgG4 responses could be combined markers to easily discriminate the different stages of pathology due to infection with S. mansoni.

Direct Evidence that Toll-like Receptor 9 (TLR9) Functionally Binds Plasmid DNA by Specific Cytosine-phosphate-guanine Motif Recognition

Cytosine-phosphate-guanine (CpG) motifs in bacterial DNA are known to activate the mammalian immune system, and this activation is thought to depend on the Toll-like receptor 9 (TLR9) signaling pathway. Previous studies strongly suggested that TLR9 is involved as the specific receptor for CpG motifs but did not provide direct evidence of their interaction. In this study, we demonstrate for the first time that murine TLR9 binds an unmethylated CpG-containing plasmid. This interaction is sequence-specific and is influenced by the methylation status of the plasmid. Furthermore, we demonstrate that this interaction leads to the activation of the NF-kappaB pathway in mTLR9-expressing cells. Our results provide a molecular basis for the interaction between CpG-DNA and TLR9.

Malaria co-infection in children influences antibody response to schistosome antigens and inflammatory markers associated with morbidity

The epidemiological coexistence of schistosomiasis and malaria is frequently observed in developing countries. Co-infection with malaria in children could influence the development of acquired immunity associated with the resistance or the pathology of schistosomiasis. In the present study, performed during May to June 1996 in Senegal, the humoral immune response to Schistosoma haematobium 28 kDa glutathione S-transferase (Sh28GST) vaccinal antigen and to soluble egg antigens (SEA) has been evaluated in individuals infected by S. haematobium. Specific immunoglobulin G3 (IgG3) and IgE responses were significantly higher in co-infected children with Plasmodium falciparum compared with children infected with S. haematobium only. In addition, circulating levels of interferon-gamma (IFN-gamma), interleukin-10 (IL-10), and soluble tumor necrosis factor receptor II (sTNF-RII), 3 parameters associated with schistosomiasis morbidity, were significantly increased in co-infected children. Taken together, this study indicated that malaria co-infection can both influence the acquired specific immune response to schistosome antigens and unbalance the regulation of inflammatory factors closely involved in schistosomiasis pathology.

Failure of a recombinant Schistosoma bovis-derived glutathione S-transferase to protect cattle against experimental Fasciola hepatica infection

The potential of a recombinant Schistosoma bovis 28-kDa glutathione S-transferase (rSb28GST) to protect cattle against Fasciola hepatica was tested in a vaccination trial. Thirty two calves were randomly divided into four groups of eight animals. Calves of the three vaccine groups received two intramuscular injections at 3 weeks interval, of 0.250mg rSb28GST in either aluminium hydroxide (Al(OH)(3)), Quil A, or PBS emulsified in an equal volume of Freund's complete adjuvant (FCA).Animals of the control group received injections of Al(OH)(3)/PBS only. All animals were challenged orally with a total of 360 metacercariae of F. hepatica, spread over 6 weeks. All groups of vaccinated animals produced measurable IgG antibody titers to rSb28GST after vaccination. Animals immunised with FCA adjuvanted vaccine had the highest and more durable antibody titers and only sera from this group recognised an approximately 24kDa protein band from F. hepatica, that is thought to be a F. hepatica GST. Despite a good antibody response differences in cumulative faecal egg output between the groups were not statistically significant. In addition, no significant difference was found between groups in terms of total worm numbers or percentage of immature flukes recovered at necropsy. In conclusion, the recombinant S. bovis 28kDa GST was not found to adequately protect cattle against experimental F. hepatica challenge, using either aluminium hydroxide, Quil A or FCA as adjuvant.

The influence of colostrum on early Schistosoma mattheei infections in calves

The study investigated whether the susceptibility of calves to an early Schistosoma mattheei infection may be modified by intake of colostrum from infected cows. Twelve calves born to non-infected mothers were randomly divided into 2 groups of 6. The animals from group 1 were fed colostrum originating from a pool collected from non-infected cows, the calves from group 2 received colostrum from a pool collected from cows infected with S. mattheei. One month after birth all calves were infected by exposure to 1000 cercariae of a local strain of S. mattheei, and perfused 12 weeks later to determine the worm- and tissue egg counts. IgG(H+L), IgG1, IgG2 and IgA levels against soluble adult worm antigen preparation of S. bovis (SWAP bovis) were analysed in both colostrum pools and in the serum from the calves collected during the study before and after receiving colostrum, then on days 7, 30, 73 and 122. Faecal egg counts were determined from day 73 onwards. The IgG(H+L), IgG1 and IgA levels of the positive colostrum pool were higher than those of the negative pool. Calves of group 2 showed significantly higher levels of IgG(H+L) and IgG1 until day 73, to reach equal levels at necropsy. Calves of group 2 showed significant reductions of 42, 28 and 42% in total worm counts, female worm counts, and tissue egg counts, respectively, and a reduction of 25% in cumulative faecal egg counts. These findings indicate that there was a significant impact of colostrum on the parasitological and serological course of early S. mattheei infections.

Transplacental transfer of schistosomal circulating anodic antigens in cows

The present work investigated the transplacental passage of circulating anodic schistosome antigens (CAA) and the production of foetal antibodies in response to antigenic stimulation in Schistosoma mattheei infected cows. Three groups were available: six calves born to non-infected cows received colostrum from a pool from non-infected cows (group 1), six calves born to non-infected cows (group 2) and six calves born to infected cows (group 3) received colostrum from a pool from infected cows. Schistosoma-specific IgG1 antibody and CAA levels were measured in the colostrum pools, the sera collected from the cows, and the sera collected from the calves at birth, after intake of colostrum and at day 30. The specific IgG1 antibody levels were significantly higher in the sera from cows of group 3. In four cows of group 3 high CAA levels were detected. The specific IgG1 antibody levels were 0.646 and 0.176 OD for the infected and non-infected colostrum pool, respectively, and the CAA levels were 5667 and 2557 pg CAA/mL, respectively. At birth high levels of specific IgG1 antibody and CAA were detected in 4 calves of group 3; levels in the other two calves were negligible. After intake of colostrum, specific IgG1 antibody levels of group 1 increased slightly at day 1 to become again insignificant at day 30. In group 2 specific IgG1 antibody levels increased significantly between days 0 and 1, to decrease, although not significantly, at day 30. Finally, in group 3 the delta OD values increased at day 1 and remained high until day 30. After intake of colostrum the CAA level increased very slightly for groups 1 and 2 to become again undetectable at day 30. In group 3 a nonsignificant decrease in CAA levels was observed at day 1 followed by a further significant decrease to reach low levels at day 30. The suggested intrauterine antigenic stimulation may be important not only for generating immune responses to natural early infections, but also for enhancing the immunogenicity and efficacy of vaccines administered to newborns.

Functional specific binding of testosterone to Schistosoma haematobium 28-kilodalton glutathione S-transferase

During parasitic disease such as schistosomiasis, sex hormones have an important influence on the age- and gender-dependent level of infection. Since mammal glutathione S-transferase (GST) has the ability to bind hormones and particularly sexual steroids to influence their transport, metabolism, and physiological action, we have evaluated the capacity of testosterone to bind the 28-kDa GST of the Schistosoma haematobium parasite (Sh28GST). For the first time, we have demonstrated a specific binding of testosterone to parasite GST protein with high affinity (K(d) = 2.57 x 10(-7) M). In addition, we have assessed the effect of this binding on Sh28GST enzymatic activity, a mechanism closely associated with the reduction of Schistosoma fecundity. We showed that testosterone has the functional ability to inhibit the Sh28GST enzymatic activity in a dose-dependent manner, suggesting that this hormone could be directly involved in an antifecundity mechanism. This effect seemed to be related to the binding of testosterone to one peptide involved in the enzymatic site (i.e., amino acids 24 to 43). During human infection, binding of sexual hormones to Schistosoma Sh28GST could play a key role in parasite metabolism, especially the decrease of fecundity, and could be involved in the sex-dependent immune response to Sh28GST that we have previously observed in infected adults.

Features of the antibody response attributable to plasmid backbone adjuvanticity after DNA immunization

DNA vaccination induces antigen-specific immune responses with characteristics distinct from other vaccination modes. In the present study, the contribution of the plasmid backbone adjuvant effect to the quality of the DNA-raised antibody response was investigated. For this purpose, three intradermal primings were compared in mice using: (1) the recombinant Schistosoma haematobium glutathione S-transferase antigen (rSh28GST): (2) rSh28GST supplemented with a non-coding plasmid; and (3) a Sh28GST-encoding plasmid. In contrast to immunization with the protein, DNA immunization elicited a very stable antibody (Ab) response over a prolonged period of time. This feature was attributed to the plasmid backbone, because co-administration of the non-coding plasmid with rSh28GST allowed the maintenance of the specific Ab response. A strong anamnestic Ab response was induced after intradermal boost with rSh28GST only in the mice primed with pMSh. This indicated that the selective ability of DNA vaccination to induce memory humoral response was independent of the plasmid backbone. In contrast the plasmid backbone was found to strongly participate in the preferential IgG2a Ab production observed. These results suggest that, following DNA immunization, the Th1-biased profile and the maintenance of the long-lived Ab response could be attributed to an adjuvant effect of the plasmid backbone during priming, whereas the strength of B-cell memory was independent of this effect.

Gender-dependent specific immune response during chronic human Schistosomiasis haematobia

The cellular and humoral acquired immune responses to Schistosoma haematobium 28 kD gluthathione S-Transferase (Sh28GST) antigen were evaluated in a Senegalese population chronically infected with S. haematobium parasite. We show a gender-dependent immune response in adult individuals presenting similar intensities of infection. Indeed, the specific IgA response and production of TGF-beta and IL-10 were found significantly higher in females compared to males. In addition, we showed that this profile was combined with a weak production of Th1-related cytokines (TNFalpha and IFNgamma) and was associated with an absence of proliferation to the antigen. A significantly higher Nuclear Matrix Protein 41/7 secretion, an apoptosis marker, was specifically observed in mononuclear blood cell cultures of females suggesting that a specific cell death process was engaged in a gender-dependent manner. This specific profile could be associated with the so-called T helper type-3 (Th3) immune response specifically promoting the production of IgA and would be developed upon the down-regulation of the specific Type-1 response by a probable cell death mechanism. This gender-dependent immune regulation, which may be under the influence of nonimmunological factors like sexual hormones, may be related to the chronicity of the infection.

Control of schistosomiasis pathology by combination of Sm28GST DNA immunization and praziquantel treatment

Today the control of schistosomiasis infection relies only on the use of praziquantel (PZQ) chemotherapy. However, PZQ treatment cannot prevent reinfection and progressive development of the pathology. We assessed in a mouse model the efficiency of a combined therapy, based on the combination of PZQ chemotherapy with Schistosoma mansoni 28-kDa glutathion S-transferase (Sm28GST) DNA vaccination, designed to limit the pathology. Following this combined therapy, the long-term survival of the mice was significantly enhanced in comparison with the survival of mice either vaccinated only or treated with PZQ only. In addition, the development of the pathology observed in the control groups was almost completely prevented in the vaccinated-PZQ-treated mice and was associated with a dramatic reduction of egg deposition in the tissues. We showed that PZQ treatment induced the unmasking of the native GST enzyme at the surface of the worms, thus permitting its neutralization by the antibodies raised by DNA immunization. This study provides insights into the synergistic mechanisms involved in an immunointervention strategy associated with chemotherapy for the control of a chronic infection and its associated pathology.

Single-dose mucosal immunization with biodegradable microparticles containing a Schistosoma mansoni antigen

The purpose of this work was to assess the immunogenicity of a single nasal or oral administration of recombinant 28-kDa glutathione S-transferase of Schistosoma mansoni (rSm28GST) entrapped by poly(lactide-co-glycolide) (PLG)- or polycaprolactone (PCL)-biodegradable microparticles. Whatever the polymer and the route of administration used, the equivalent of 100 microg of entrapped rSm28GST induced a long-lasting and stable antigen-specific serum antibody response, with a peak at 9 to 10 weeks following immunization. Isotype profiles were comparable, with immunoglobulin G1 being the predominant isotype produced. The abilities of specific antisera to neutralize the rSm28GST enzymatic activity have been used as criteria of immune response quality. Pooled 10-week sera from mice receiving PLG microparticles by the nasal or oral route neutralized the rSm28GST enzymatic activity, whereas sera of mice receiving either PCL microparticles, free rSm28GST, or empty microparticles inefficiently neutralized this enzymatic activity. Finally, this study shows that a single administration of these microparticles could provide distinct and timely release pulses of microencapsulated antigen, which might greatly facilitate future vaccine development.

Bordetella pertussis filamentous hemagglutinin enhances the immunogenicity of liposome-delivered antigen administered intranasally

In an attempt to increase the immunogenicity of mucosally delivered antigens, we incorporated the Bordetella pertussis filamentous hemagglutinin (FHA) adhesin into liposomes containing the glutathione S-transferase of Schistosoma mansoni (Sm28GST) as a model antigen. Outbred mice immunized twice intranasally with liposomes containing a constant suboptimal dose of Sm28GST and increasing doses of FHA produced anti-Sm28GST antibodies in a FHA dose-dependent manner. The addition of 3 microg of FHA to the liposomes induced more than 10-fold-higher anti-Sm28GST antibody titers, compared to those induced by liposomes without FHA. The presence of FHA did not alter the nature of the humoral immune response, and the sera contained anti-Sm28GST immunoglobulin G1 (IgG1), IgG2a, and IgG2b. However, anti-Sm28GST IgA was only detected when at least 3 microg of FHA was added to the preparation. These results show a promising potential for FHA to enhance the immunogenicity of mucosally administered antigens incorporated into liposomes.

Intradermal immunization of rats with plasmid DNA encoding Schistosoma mansoni 28 kDa glutathione S-transferase

Direct administration of plasmid DNA encoding an antigen represents an attractive approach to vaccination against infectious diseases, particularly in developing countries where easy-to-handle and cost-effective vaccines are needed. We have investigated the potential of DNA immunization to induce a specific antibody response against Schistosoma mansoni, using plasmid-DNA encoding the protective antigen, S. mansoni 28 kDa glutathione S-transferase (Sm28GST). Since S. mansoni parasite penetrates into its host through the skin, this tissue was chosen for plasmid DNA delivery. Following plasmid DNA administration into the skin of rats, the parasite antigen was detected in skin cells by immunohistochemistry. Three administrations of 200 micrograms plasmid at 14 day intervals led to the induction of a long-lasting specific IgG antibody response in the sera of immunized rats, with a predominance of IgG2a and IgG2b subclasses. Sera of immunized animals were able to mediate antibody-dependent cellular cytotoxicity in vitro, leading to the specific killing of parasite larvae. A parasite challenge performed on plasmid DNA-immunized animals induced a strong and rapid boosting effect on the specific IgG antibody response. These results demonstrate the potential of genetic immunization via the skin with plasmid DNA encoding Sm28GST for inducing immune responses with protective patterns against an S. mansoni infection.

Intranasal priming with recombinant Bordetella pertussis for the induction of a systemic immune response against a heterologous antigen

One of the current goals in vaccine development is the noninvasive administration of protective antigens via mucosal surfaces. In this context, the gut-associated lymphoid tissues have already been extensively explored. Vaccination via the nasal route has only recently been the focus of intensive investigation, and no live vector specifically designed for the respiratory mucosa is yet available. In this study we show that intranasal administration of the recombinant Bordetella pertussis BPGR60, producing the Schistosoma mansoni 28-kDa glutathione S-transferase (Sm28GST) protective antigen fused to filamentous hemagglutinin, induces priming in mice for the production of serum antibodies. In addition to significant levels of anti-Sm28GST immunoglobulin A (IgA) antibodies, high levels of anti-Sm28GST serum antibodies were obtained after intranasal boost with the purified antigen or infection with S. mansoni following intranasal priming with BPGR60. These antibodies were of the IgG1, IgG2a, and IgG2b isotypes, suggesting a mixed immune response. No priming was observed in animals that had received nonrecombinant B. pertussis or purified Sm28GST, indicating specific priming by BPGR60. This priming was also evident in immune protection against S. mansoni challenge. Significant protection against worm burden and egg output was obtained in mice primed with BPGR60 and intranasally boosted with purified Sm28GST. A lower but still significant degree of protection against egg output was also obtained in mice infected with a single dose of BPGR60. These results indicate that intranasal administration of recombinant B. pertussis can prime for serum antibody responses against a foreign antigen and for heterologous protection.

Mucosal vaccination against schistosomiasis using liposome-associated Sm 28 kDa glutathione S-transferase

A variety of experimental models have shown that immunization using the glutathione S-transferase from Schistosoma mansoni (Sm28GST) can induce protective immunity against this parasite. This immunity has been related to the production of Th2 type antibodies against the antigen in both mice and humans. The work presented in this paper describes the development of a mucosal immunization protocol using liposomes which is designed to promote production of specific antibodies of isotypes related to a Th2 immune response. The liposomes were multilamellar and composed of various synthetic phospholipid mixtures. The liposome vector was used to convey the Sm28GST antigen to gut associated lymphoid tissue. The association of the Sm28GST antigen with liposomes containing different lipid mixtures was initially studied. The degree of interaction of the antigen was found to increase with the hydrocarbon chain length of the lipids used. It was demonstrated that the protein was present on both the inner and the outer membranes of the liposome vesicles. It was also shown that the major epitopes of Sm28GST were accessible to specific antibodies, confirming a conservation of its main antigenic features. Additionally, enzymatic activity of the protein/liposome complex was also demonstrated, indicating a conservation of the tertiary structure of the protein. An optimal Sm28GST/ liposome complex was established and administered orally to mice. This treatment resulted in both a mucosal and systemic immune response to the antigen Sm28GST. This was demonstrated by the detection of specific IgA in gut washes and specific IgG1, IgG2b in sera. Immunization by Sm28GST/liposome complex followed by challenge with parasite showed that Sm28GST given orally in these conditions bore protective activity. This last result opens the possibility of mucosal vaccination against schistosomiasis.

Induction of mucosal immune responses against a heterologous antigen fused to filamentous hemagglutinin after intranasal immunization with recombinant Bordetella pertussis

Live vaccine vectors are usually very effective and generally elicit immune responses of higher magnitude and longer duration than nonliving vectors. Consequently, much attention has been turned to the engineering of oral pathogens for the delivery of foreign antigens to the gut-associated lymphoid tissues. However, no bacterial vector has yet been designed to specifically take advantage of the nasal route of mucosal vaccination. Herein we describe a genetic system for the expression of heterologous antigens fused to the filamentous hemagglutinin (FHA) in Bordetella pertussis. The Schistosoma mansoni glutathione S-transferase (Sm28GST) fused to FHA was detected at the cell surface and in the culture supernatants of recombinant B. pertussis. The mouse colonization capacity and autoagglutination of the recombinant microorganism were indistinguishable from those of the wild-type strain. In addition, and in contrast to the wild-type strain, a single intranasal administration of the recombinant strain induced both IgA and IgG antibodies against Sm28GST and against FHA in the bronchoalveolar lavage fluids. No anti-Sm28GST antibodies were detected in the serum, strongly suggesting that the observed immune response was of mucosal origin. This demonstrates, to our knowledge, for the first time that recombinant respiratory pathogens can induce mucosal immune responses against heterologous antigens, and this may constitute a first step toward the development of combined live vaccines administrable via the respiratory route.

Cloning of the gene encoding a Schistosoma mansoni antigen homologous to human Ro/SS-A autoantigen

A cDNA library was constructed from the mRNA of adult worms of Schistomsoma mansoni in the expression vector lambda gt11 and screened with a rabbit antiserum raised against a 60-65-kDa electroeluted adult worm fraction. Two overlapping clones were selected and a partial nucleotide sequence was deduced (1172 bp). The full-length sequence was obtained by the amplification of the 5' end of first strand cDNA using PCR. The overall mRNA size was 1335 nt including a 25 nt 5' non-coding region and a 131 nt untranslated region with the poly(A) tail. The predicted amino acid sequence of 393 aa (45 kDa) has 52% identity with the human Ro/SS-A autoantigen, which is considered to be the human calreticulin. As for the human Ro/SS-A, the protein encoded by the cDNA described here contains a hydrophobic leader sequence and a carboxyl terminal sequence, HDEL consensus signal sequence for retention in the ER. An antiserum raised against the fusion protein of one clone recognized a 58-kDa antigen in homogenates of cercariae and of adult worms. The expression of the protein in the pGEX-2T fusion system allowed us to show the presence of specific antibodies in S. mansoni infected patients' sera and in the sera of patients with systemic lupus erythematosus, reflecting a cross-immunoreactivity between the S. mansoni protein and the human calreticulin autoantigen.

Immunological crossreactivity between the human immunodeficiency virus type 1 virion infectivity factor and a 170-kD surface antigen of Schistosoma mansoni

A monoclonal antibody (mAb) directed against a synthetic peptide derived from the sequence of the human immunodeficiency virus type 1 (HIV-1) regulatory protein virion infectivity factor (vif) labeled the surface of Schistosoma mansoni schistosomula by indirect immunofluorescence. Western blotting showed that two S. mansoni proteins of 170 and 65 kD were recognized by the mAb. Sera from 20% of S. mansoni-infected HIV-seronegative individuals tested recognized the PS4 peptide in an ELISA as did sera from S. mansoni-infected rats. Sera from individuals seropositive for HIV-1, but without schistosomiasis, that reacted with the vif peptide also recognized a 170-kD S. mansoni protein. This crossreactive S. mansoni antigen appears to be a target of immunity in vivo since passive transfer of the mAb VIF-CD3 to naive rats had a protective effect against a challenge infection with S. mansoni cercariae.