Denis Boulanger

Impact of child malnutrition on the specific anti-Plasmodium falciparum antibody response

BackgroundIn sub-Saharan Africa, preschool children represent the population most vulnerable to malaria and malnutrition. It is widely recognized that malnutrition compromises the immune function, resulting in higher risk of infection. However, very few studies have investigated the relationship between malaria, malnutrition and specific immunity. In the present study, the anti-Plasmodium falciparum IgG antibody (Ab) response was evaluated in children according to the type of malnutrition.MethodsAnthropometric assessment and blood sample collection were carried out during a cross-sectional survey including rural Senegalese preschool children. This cross-sectional survey was conducted in July 2003 at the onset of the rainy season. Malnutrition was defined as stunting (height-for-age <-2 z-scores) or wasting (weight-for-height <-2 z-scores). The analysis was performed on all malnourished children in July (n = 161, either stunted, n = 142 or wasted, n = 19), pair-matched to well-nourished controls. The IgG Ab response to P. falciparum whole extracts (schizont antigens) was assessed by ELISA in sera of the included children.ResultsBoth the prevalence of anti-malarial immune responders and specific IgG Ab levels were significantly lower in malnourished children than in controls. Depending on the type of malnutrition, wasted children and stunted children presented a lower specific IgG Ab response than their respective controls, but this difference was significant only in stunted children (P = 0.026). This down-regulation of the specific Ab response seemed to be explained by severely stunted children (HAZ ≤ -2.5) compared to their controls (P = 0.03), while no significant difference was observed in mildly stunted children (-2.5 < HAZ <-2.0). The influence of child malnutrition on the specific anti-P. falciparum Ab response appeared to be independent of the intensity of infection.ConclusionChild malnutrition, and particularly stunting, may down-regulate the anti-P. falciparum Ab response, both in terms of prevalence of immune responders and specific IgG Ab levels. This study provides further evidence for the influence of malnutrition on the specific anti-malarial immune response and points to the importance of taking into account child malnutrition in malaria epidemiological studies and vaccine trials.

Human antibody response to Anopheles gambiae saliva: an immuno-epidemiological biomarker to evaluate the efficacy of insecticide-treated nets in malaria vector control.

For the fight against malaria, the World Health Organization (WHO) has emphasized the need for indicators to evaluate the efficacy of vector-control strategies. This study investigates a potential immunological marker, based on human antibody responses to Anopheles saliva, as a new indicator to evaluate the efficacy of insecticide-treated nets (ITNs). Parasitological, entomological, and immunological assessments were carried out in children and adults from a malaria-endemic region of Angola before and after the introduction of ITNs. Immunoglobulin G (IgG) levels to An. gambiae saliva were positively associated with the intensity of An. gambiae exposure and malaria infection. A significant decrease in the anti-saliva IgG response was observed after the introduction of ITNs, and this was associated with a drop in parasite load. This study represents the first stage in the development of a new indicator to evaluate the efficacy of malaria vector-control strategies, which could apply in other arthropod vector-borne diseases.

Vaccine potential of a recombinant glutathione S-transferase cloned from Schistosoma haematobium in primates experimentally infected with an homologous challenge

Patas monkeys were twice immunized with a Schistosoma haematobium-derived recombinant glutathione S-transferase (Sh28GST) then challenged with an homologous calibrated challenge. BCG and Freunds Complete Adjuvant (FCA) were used as adjuvants in two distinct protocols. Specific IgG and IgA antibody responses were intense and homogeneous in the animals receiving Sh28GST in the presence of FCA, whereas BCG could only induce moderate and heterogeneous antibody titres. No significant effect on worm burdens was evidenced 36 weeks post-infection in either group of Sh28GST-immunized animals compared to their matched controls receiving an irrelevant protein. Although not significant, 50% reductions in the numbers of eggs located in all tissues (FCA group) and in the urogenital system (BCG group) were noted. Moreover, the total number of excreted eggs was dramatically diminished by 60% and 77% in the BCG and FCA groups, respectively. These reductions reached 75% and 80% in the urines of vaccinated monkeys. Bladder pathology was also reduced in the animals displaying the lowest urinary egg excretions. There was no clear positive or negative correlate between antibody responses and individual levels of protection. Taken as a whole, our results show that Sh28GST was capable of significantly reducing S. haematobium worm fecundity in experimentally infected primates. Although FCA induced higher levels of protection, the efficacy of BCG as an adjuvant appeared sufficient to justify consideration of the future application of this new formulation as a vaccine against human urogenital schistosomosis.

Development of a Vaccine Strategy against Human and Bovine Schistosomiasis. Background and Update

Schistosomiasis is a chronic and debilitating parasitic disease that affects over 200 million people throughout the world and causes about 500,000 deaths annually. Two specific characteristics of schistosome infection are of primordial importance to the development of a vaccine: schistosomes do not multiply within the tissues of their definitive hosts (unlike protozoan parasites) and a partial non-sterilizing immunity can have a marked effect on the incidence of pathology and on disease transmission. Since viable eggs are the cause of disease pathology, a reduction in worm fecundity whether or not accompanied by a reduction in parasite burden is a sufficient goal for vaccine induced immunity. We originally showed that IgE antibodies played in experimental models a pivotal role for the development of protective immunity. These laboratory findings have been now confirmed in human populations. Following the molecular cloning and expression of a protein 28 kDa protein of Schistosoma mansoni and its identification as a glutathion S-transferase, immunization experiments have been undertaken in several animal species (rats, mice, baboons). Together with a significant reduction in parasite burden, vaccination with Sm28 GST was recently shown to reduce significantly parasite fecundity and egg viability leading to a decrease in liver pathology. Whereas IgE antibodies were shown to be correlated with protection against infection, IgA antibodies have been identified as one of the factors affecting egg laying and viability. In human populations, a close association was found between IgA antibody production to Sm28 GST and the decrease of egg output.(ABSTRACT TRUNCATED AT 250 WORDS)

Schistosoma bovis: vaccine effects of a recombinant homologous glutathione S-transferase in sheep.

The economic importance of the trematode Schistosoma bovis in African livestock has justified the development of a specific vaccine. Administered preventively to sheep, rSb28GST--the only molecule cloned from S. bovis which has demonstrated vaccine potentialities in goats and cattle--reduced the mean worm burden in vaccinated animals and improved their health status compared with that of non-vaccinated controls. As in goats, but not in bovines, the fecundity of the settled worm pairs was not modified. Therefore, rSb28GST can be proposed as a universal tool for the prevention of clinical disorders engendered by the main schistosome species affecting domestic ruminants in the African continent.

The oral route as a potential way of transmission of Schistosoma bovis in goats.

The infectivity of Schistosoma bovis cercariae administered orally was evaluated in Sahelian goats. Compared to the percutaneous route, a single massive oral dose resulted in a worm burden and in fecal egg excretion reduced by one-half. Surprisingly, tissue egg counts were increased by more than 4-fold. Fecundity of individual female schistosomes was, therefore, markedly increased. When infective doses were administered weekly for 20 wk, both worm and egg burdens were doubled without modification of the individual worm pair fecundity. Repeated oral infections seem to have induced an acquired tolerance toward parasite antigens. These results confirm the epidemiologic relevance of the oral route in a host species inclined to become infected through drinking water rather than percutaneous exposures.

THE WHO COLLABORATING CENTRE FOR RESEARCH AND CONTROL OF SCHISTOSOMIASIS AT NIAMEY, NIGER

The Centre de Recherche sur les Méningites et les Schistosomes (CERMES) is a research institute depending on the Organisation de Coordination et de Coopération pour la lutte contre les Grandes Endémies--a West African Organization for Public Health--devoted to the studies on schistosomiasis and meningitis. The staff includes 32 persons with 11 scientists and one financial officer. The activities of the CERMES involving schistosomiasis concern three research units: (a) ecology of human and animal schistosomiasis transmission; the CERMES defined the different patterns of schistosomiasis transmission in Niger (involving African dry savana); in this field, we have shown, (i) the existence of important variability in conditions of transmission of S. haematobium and, (ii) natural hybridization between parasitic species of the ruminants (S. bovis and S. curassoni) and genetic interaction between human and animal parasites; (b) definition of morbidity indicators usable for rapid assessment methods, for appraisal of the severity of the disease and for the evaluation of the efficiency of control methods; we have established the correlation between ultrasonographic data and some cheap and simple field indicators; (c) immune response and protective immunity induced by recombinant glutathion S-transferase (Sm28, Sb28 and Sh28) in homologous and heterologous animal models including goats, sheep and non human primates (Erythrocebus patas). In Niger, we participate in all control programs against schistosomiasis to define control strategies, to supervise operations and to participate in their evaluation with external experts. International collaborations constitute a frame including four laboratories in Africa and six laboratories in developed countries (Europe and USA).

GP38, P28-I and P28-II: candidates for a vaccine against Schistosomiasis

Three antigens protective against Schistosoma mansoni have been extensively characterized. The schistosomulum surface antigen GP38 possesses an immunodominant carbohydrate epitope of which the structure has been defined. Protection can be achieved via the transfer of monoclonal antibodies recognizing the epitope or by immunization with anti-idiotype monoclonal antibodies. The glycan epitope is shared with the intermediate host, Biomphalaria glabrata as well as being present on other molluscs, including the Keyhole Limpet. A group of molecules at 28 kDa were initially characterized in adult worms and shown to protect rats and mice against a challenge infection. One of these molecules, P28-I, was cloned and expressed in E. coli, yeast and vaccinia virus. The recombinant antigen significantly protected rats, hamsters and baboons against a challenge infection. P28-I is a glutathione-S-transferase and the recombinant antigen produced in yeast exhibits the enzyme activity and has been purified to homogeneity by affinity chromatography. A second P28 antigen, P28-II, has also been cloned, fully sequenced and expressed. This recombinant antigen also protects against S. mansoni infection.

Immunoglobulin G Antibody Profiles Against Anopheles Salivary Proteins in Domestic Animals in Senegal

ABSTRACT Although domestic animals may not be permissive for Plasmodium, they could nevertheless play a role in the epidemiology of malaria by attracting Anopheles away from humans. To investigate interactions between domestic animals and mosquitoes, we assayed immunoglobulin G (IgG) antibodies directed against the salivary proteins of Anopheles gambiae in domestic animals living in Senegalese villages where malaria is endemic. By Western blotting, sera from bovines (n = 6), ovines (n = 36), and caprines (n = 36) did not react with Anopheles whole saliva. In contrast, equine sera recognized proteins in both saliva and salivary gland extracts. Two of the major immunogens (32 and 72 kDa) were also reactive in extracts from other major mosquito genera (Aedes and Culex), but reactions to Anophehs-specific antigens were detected in 12 of 17 horses. These data suggest that horses strongly react to Anopheles bites, and further experiments on horses are warranted to investigate the impact of this domestic animal species on the transmission of human malaria.