Dynamics of PfEMP1 Antibody Profile From Birth to 12 Months of Age in Beninese Infants.

BACKGROUND: Plasmodium falciparum-infected erythrocytes bind to specific endothelial cell receptors via members of the PfEMP1 family exported onto the erythrocyte surface. These interactions are mediated by different types of cysteine-rich interdomain region (CIDR) domains found in the N-terminal region of all PfEMP1. CIDRα1 domains bind endothelial protein C receptor (EPCR), CIDRα2-6 domains bind CD36, whereas the receptor specificity of CIDRß/γ/δ domains is unknown. METHODS: In this study, we investigated the level of immunoglobulin (Ig)G targeting the different types of PfEMP1 CIDR during the first year of life. We used plasma collected longitudinally from children of pregnant women who had been followed closely through pregnancy. RESULTS: Antibodies to CIDRα1 domains were more frequent in cord blood compared with antibodies to CIDRα2-6 domains. Higher IgG levels to EPCR-binding CIDRα1 variants positively correlated with the timing of first infections. Antibodies to all PfEMP1 types declined at similar rates to the point of disappearance over the first 6 months of life. At 12 months, children had acquired antibody to all types of CIDR domains, mostly in children with documented P falciparum infections. CONCLUSIONS: These observations agree with the notion that the timing and phenotype of first P falciparum infections in life are influenced by the immune status of the mother.

Determinants of primary healthcare seeking behaviours for children during the first 18 months of life in Benin.

Background: Primary healthcare is a key element of management of childhood illness in Africa. The objectives were to identify primary care seeking determinants among infants and young children up to 18 mo in a birth cohort from Benin. Methods: From 2007 to 2009 in Benin, a birth cohort was followed until the age of 18 mo in three health centres. Multilevel Poisson regression models were fitted to identify the factors related to the monthly number of consultations. Maternal and newborn characteristics and infant general health parameters were considered. Results: A total of 566 children were followed. On average, 0.46 consultations per month per child were recorded. The number of consultations was significantly lower after the first 6 mo of life (p<0.001). A distance >1000 m was associated with fewer consultations (p=0.01). Primiparity was significantly associated with higher care seeking (relative risk 1.17 [95% CI 1.05 to 1.30], p<0.01). No child characteristics at birth were significantly associated with the number of consultations (all p>0.16). Conclusions: Development of health structures and improvement of access remain important goals for strengthening of the primary care health system. Studying factors of care seeking behaviour, like parity, can help to identify women more prone to seek care for their child during the first year of life.

Preferential expression of domain cassettes 4, 8 and 13 of Plasmodium falciparum erythrocyte membrane protein 1 in severe malaria imported in France.

OBJECTIVES: Severe Plasmodium falciparum malaria (SM) involves cytoadhesion of parasitized red blood cells, mediated by P. falciparum erythrocyte membrane protein 1, which is encoded by var genes. Expression of var gene group A and B or encoding domain cassettes DC4, DC5, DC8 and DC13 has been implicated in SM in African children, but no data exist in the context of imported malaria. The aim of this study was to investigate var gene expression linked to clinical presentation and host factors in SM imported into France. METHODS: Expression level of var gene groups A, B, C, var1, var2csa, var3 and var genes encoding DC4, DC5, DC8 and DC13 was measured by quantitative RT-PCR and expressed in transcript units. Seventy SM and 48 uncomplicated malaria (UM) P. falciparum cases were analysed according to disease severity, epidemiological characteristics (migrants or travellers) and anti-P. falciparum antibodies. Cluster analysis was performed to identify gene expression profiles. RESULTS: Var1 and B/C expression were higher in UM than SM (0.66 (0-1.1) and 1.88 (1.3-2.4); p <0.04, respectively). Group C expression differed between migrants and travellers (0.21 (0-0.75) versus 0 (0-0); p 0.002). Group A differed in naive and pre-exposed patients (1.1 (0.7-1.5) versus 0.4 (0-1.1); p 0.01). Population clusters revealed increased expression from group A and B var genes, and DC4, DC8 and DC13 in SM. CONCLUSIONS: These results corroborate the implication of DC4, DC8 and DC13 in severe imported malaria cases as African children, and their expression depends of host factors.

Antibiotics usage in infants during the first 18 months of life in Benin: a population-based cohort study.

Data centered on antibiotics usage and their determinants in African pediatric populations are limited. In order to define the determinants of antibiotics prescriptions (ABPr), we analyzed the data of a birth cohort in Benin. From 2007 to 2009, 538 infants were followed from birth to 18 months in three different health centers. The following determinants were assessed: infants' clinical findings at consultations, mothers' and children's characteristics at birth, and health parameters recorded at scheduled follow-up of general health parameters. Multilevel logistic models were performed for analysis. Among the 4394 consultations, fever represented 53.7 % of consultations, 64.1 % of which were non-malarial fevers. Antibiotics were prescribed during 44.2 % of the consultations and the proportion of ABPr differed significantly among health centers (p < 10(-3)). Nearly 40 % of ABPr were related to children without fever. During the first semester of life, the percentage of ABPr was twice lower than after (27.4 vs. 54.7, p < 10(-3)). Respiratory and enteric symptoms were positively associated with ABPr (p < 10(-3)). Malaria was significantly associated with a lower ABPr after the first semester [odds ratio (OR) = 0.55, 95 % confidence interval (CI) = 0.44-0.67, p < 10(-3)]. No maternal and child at-birth characteristics were associated with ABPr. ABPr was positively associated with a low breastfeeding score (p < 10(-3)). Studies on the rational use of antibiotics in this population should give priority to children more than 6 months of age, without malaria, and with respiratory and/or enteric symptoms. Our data also advocate for studies specifically designed to assess and improve healthcare providers' compliance to guidelines on antibiotics usage.

Computational Fluid Dynamic Simulations of Maternal Circulation: Wall Shear Stress in the Human Placenta and Its Biological Implications.

INTRODUCTION: In the human placenta the maternal blood circulates in the intervillous space (IVS). The syncytiotrophoblast (STB) is in direct contact with maternal blood. The wall shear stress (WSS) exerted by the maternal blood flow on the STB has not been evaluated. Our objective was to determine the physiological WSS exerted on the surface of the STB during the third trimester of pregnancy. MATERIAL AND METHODS: To gain insight into the shear stress levels that the STB is expected to experience in vivo, we have formulated three different computational models of varying levels of complexity that reflect different physical representations of the IVS. Computations of the flow fields in all models were performed using the CFD module of the finite element code COMSOL Multiphysics 4.4. The mean velocity of maternal blood in the IVS during the third trimester was measured in vivo with dynamic MRI (0.94±0.14 mm.s-1). To investigate if the in silico results are consistent with physiological observations, we studied the cytoadhesion of human parasitized (Plasmodium falciparum) erythrocytes to primary human STB cultures, in flow conditions with different WSS values. RESULTS: The WSS applied to the STB is highly heterogeneous in the IVS. The estimated average values are relatively low (0.5±0.2 to 2.3±1.1 dyn.cm-2). The increase of WSS from 0.15 to 5 dyn.cm-2 was associated with a significant decrease of infected erythrocyte cytoadhesion. No cytoadhesion of infected erythrocytes was observed above 5 dyn.cm-2 applied for one hour. CONCLUSION: Our study provides for the first time a WSS estimation in the maternal placental circulation. In spite of high maternal blood flow rates, the average WSS applied at the surface of the chorionic villi is low (<5 dyn.cm-2). These results provide the basis for future physiologically-relevant in vitro studies of the biological effects of WSS on the STB.

Towards a vaccine against pregnancy-associated malaria.

The consequences of pregnancy-associated malaria on pregnant women (anaemia), their babies (birth weight reduction), and infants (increased morbidity and mortality) are well documented. Field observations during the last decade have underlined the key role of the interactions between P. falciparum variable surface antigens expressed on infected erythrocytes and a novel receptor: chondroitin sulfate A (CSA) for the placental sequestration of infected erythrocytes. Identification of a distinct P. folciparum erythrocyte membrane protein 1 (PfEMP1) variant, VAR2CSA, as the dominant variant surface antigen and as a clinically important target for protective immune response to pregnancyassociated malaria has raised hope for developing a new preventive strategy based on inducing these immune responses by vaccination. However, despite particular structure and interclonal conservation of VAR2CSA among other PfEMP1, significant challenges still exist concerning the development of a VAR2CSA-based vaccine with profound efficacy.

Dynamics of anti-VAR2CSA immunoglobulin G response in a cohort of senegalese pregnant women.

BACKGROUND: Pregnancy-associated malaria (PAM) is precipitated by the accumulation of parasites in the placental intervillous spaces and causes maternal anemia and low birth weight. In PAM, placental parasites adhere to chondroitin sulfate A (CSA) through a unique set of variant surface antigens (VSAPAM). Several studies have shown that 1 var gene, var2csa, is transcribed at high levels and expressed in CSA-binding Plasmodium falciparum parasites. METHODS: Plasma levels of anti-VAR2CSA immunoglobulin G (IgG) in Senegalese women were measured during pregnancy by enzyme-linked immunosorbent assay, using 3 recombinant proteins representing 3 domains of the var2csa gene product. RESULTS: The 3 recombinant proteins were specifically recognized by plasma from pregnant women but not by control plasma. A parity-dependent recognition pattern was observed with 2 of the 3 VAR2CSA antigens. A kinetic study demonstrated that a single P. falciparum infection was able to trigger a VAR2CSA-specific antibody response. Among women with infected placentas, women with high anti-VAR2CSA IgG levels at enrollment were more likely to present with a past infection than with an acute/chronic infection. CONCLUSIONS: Anti-VAR2CSA IgGs are involved in clinical protection against pregnancy-associated malaria and strengthens the hope for making a VAR2CSA-based vaccine.

Efficacy of permethrin-impregnated bed nets on malaria control in a hyperendemic area in Irian Jaya, Indonesia III. Antibodies to circumsporozoite protein and ring-infected erythrocyte surface antigen.

A two years intervention study was carried out using permethrin impregnated bed nets in a hyperendemic area, in Irian Jaya, Indonesia. To assess the influence of this intervention on natural immunity, concurrent immunological studies to determine levels of antibodies to the circumsporozoite (CS) and ring-infected erythrocyte surface antigen (RESA) proteins were conducted. Prevalence and titers of immunoglobulins (Ig)G and IgG subclasses were periodically measured in 138 individuals (30 children under the age of ten and 108 villagers ten years old and older). In the younger group, seropositivity of total IgG against CS fluctuated according to the parasite infection rates; however, IgG seropositive reaction against RESA gradually increased. In the older age group, seropositivity of both kinds of antibodies was stable during the whole study period. Nevertheless, the geometric mean titers of total IgG against CS and RESA were significantly reduced in this latter group in individuals who contained these antibodies before and after intervention. The geometric mean titer of IgG3 subclass against RESA was decreased at a highly significant level (p = 0.0005), and that of IgG4 against the same antigen was also decreased although to a lesser extent (p = 0.02).

Relationship between entomological inoculation rate, Plasmodium falciparum prevalence rate, and incidence of malaria attack in rural Gabon.

To assess the relationships between variations of Plasmodium falciparum transmission and those of peripheral parasitaemia prevalence or malaria attack incidence rates in regions with limited fluctuations of transmission, we conducted a follow-up in two Gabonese populations. Entomological surveys were carried out from May 1995 to April 1996 in Dienga, and from May 1998 to April 1999 in Benguia. In Dienga, malaria transmission was seasonal, being not detected during two 3-month periods. Mean entomological inoculation rate (EIR) was 0.28 infective bite/person/night. In Benguia, malaria transmission was perennial with seasonal fluctuations, mean EIR being 0.76 infective bite/person/night. In Dienga, 301 schoolchildren were followed from October 1995 to March 1996. Clinical malaria attack was defined as fever associated with >5000 parasites/microl of blood. P. falciparum prevalence varied from 28 to 42%, and monthly malaria attack incidence from 30 to 169 per thousand. In Benguia, the entire population (122 persons) was followed from November 1998 to April 1999. Prevalence varied from 22 to 50%, and monthly malaria attack incidence from 52 to 179 per thousand. In each area, entomological variations were not related to parasite prevalence, but preceded malaria attack incidence with 1- or 2-month time lag, corresponding to the pre-patency period that differs in the two populations, possibly according to differences in immunity related to parasite transmission.

Malaria prevention strategies.

Acute and severe consequences of pregnancy-associated malaria (PAM), such as materno-fetal death or cerebral malaria, seem limited to unstable malaria areas. In areas of stable endemicity, the main consequences are maternal anaemia and low birth weight (LBW) babies, particularly in primigravidae. Placental malaria seems more frequent and its consequences more severe in HIV-infected women. Since 1964, several chemoprophylaxis controlled trials have been undertaken, mainly in Tropical Africa where malaria is stable. Most showed an increase in mean birth weight in the prophylaxis group, especially among primigravidae. Similar findings were made with anaemia. Prophylaxis seems less effective in the case of HIV-malaria co-infection, which may require an increase in the number of doses. At present, intermittent treatment with sulfadoxine-pyrimethamine given twice or thrice during pregnancy in antenatal clinics seems the best policy for preventing PAM. Such effective prophylaxis should be integrated with other antenatal clinic services. Recently identified molecular receptors involved in cytoadherence of parasitized erythrocytes to placenta could yield new therapeutic or vaccine approaches, specifically targeted to pregnant women.

[Malaria during pregnancy: consequences and interventional perspectives]. / Paludisme associé à la grossesse: conséquences et perspectives d'intervention.

The impact of malaria during pregnancy varies greatly according to the intensity of transmission. Severe acute complications including cerebral malaria or materno-fetal death seem to be confined to areas of unstable transmission where malaria is uncommon except during epidemics. In areas of stable endemicity, the main consequences are maternal anemia and intra-uterine growth retardation resulting in low birthweight (LBW) particularly after first pregnancies. Recent studies have demonstrated that frequency and severity of placental malaria are greater in pregnant women with concurrent HIV infection. Since 1964 several controlled trials have been conducted to evaluate chemoprophylaxis in pregnant women mainly in tropical Africa where malaria transmission is stable. Findings have usually demonstrated an increase in mean birthweight after prophylaxis especially among primigravidae. Prophylaxis also had beneficial effects on anemia. Another finding of these trials was that prevention is less effective for women with HIV co-infection and that higher doses may therefore be required in such cases. In our opinion prophylaxis should be actively promoted as a routine public health measure for pregnant women in endemic areas. Current recommendations call for the use of a sulfadoxine-pyrimethamine twice or three times during pregnancy in antenatal clinics. This combination is more effective as a result of strong resistance of parasites to chloroquine. High cost and possible adverse effects in pregnant women prohibit routine use of mefloquine in developing countries. Integration of malaria prophylaxis into antenatal care services with nutrition and immunization measures should enhance the overall efficacy of prevention in outlying clinical facilities. Recent identification of molecular receptors involved in the cytoadherence of parasitized red blood cells to the placenta may lead to the development of new therapeutic or vaccinal approaches for pregnant women.

Erythrocyte binding antigen (EBA-175) of Plasmodium falciparum: improved genotype determination by nested polymerase chain reaction.

We have designed primers to the conserved region of the erythrocyte binding antigen (EBA)-175 gene which amplify specifically the two alleles by polymerase chain reaction (PCR) and by nested PCR. This approach provides a specific, sensitive and rapid method for genotype determination in a large number of Plasmodium falciparum field isolates.

Acquisition and decay of antibodies to pregnancy-associated variant antigens on the surface of Plasmodium falciparum-infected erythrocytes that protect against placental parasitemia.

Otherwise clinically immune women in areas endemic for malaria are highly susceptible to Plasmodium falciparum malaria during their first pregnancy. Pregnancy-associated malaria (PAM) is characterized by placental accumulation of infected erythrocytes that adhere to chondroitin sulfate A (CSA). Susceptibility to PAM decreases with increasing parity, apparently due to acquisition of antibodies directed against the variant surface antigens (VSAs) that mediate the adhesion to CSA (VSA(CSA)). This study found that levels of VSA(CSA)-specific antibodies depend on endemicity, that anti-VSA(CSA) IgG is acquired during gestation week 20, and that plasma levels of the antibodies decline during the postpartum period. There is evidence that VSA(CSA)-specific antibodies are linked to placental infection and that high antibody levels contribute to the control of placental infection by inhibiting parasite adhesion to CSA. Data suggest that VSA(CSA) is a target for vaccination against PAM.

Plasmodium falciparum induces a Th1/Th2 disequilibrium, favoring the Th1-type pathway, in the human placenta.

During pregnancy, a local and systemic Th2 bias of maternal immunity favors Th1-dependent infections such as malaria. This study measured cytokines secreted in cultures of chorionic villi, placental blood cells (PBC), and serum in term placentas from 88 malaria-infected and -noninfected Cameroon women. Interleukin (IL)--2 and --4 were consistently low; IL-1 beta, IL-6, granulocyte-macrophage colony-stimulating factor, and transforming growth factor (TGF)--beta 2 were highest in villi cultures. Tumor necrosis factor (TNF)--alpha, interferon (IFN)--gamma, and IL-10 were highest in PBC cultures. Malaria placental infection increased Th1-type cytokines, whereas Th2-type cytokines and TGF-beta 2 were unchanged. Addition of lipopolysaccharide or infected erythrocytes to cultures increased TNF-alpha, IL-1 beta, IL-6, and IL-10 secretions but not those of IFN-gamma and IL-4. Overall, Plasmodium falciparum induced a placental immune response involving both Th1- and Th2-type cell activation. Although the Th1 pathway was favored, IL-10 secretion was also increased, and this increase should be effective in protecting the placenta by controlling the negative effects of Th1 cytokines on pregnancy.

HLA alleles in relation to specific immunity to liver stage antigen-1 from plasmodium falciparum in Gabon.

Cellular responses to synthetic peptides from the Liver Stage Antigen-1 (LSA-1) from Plasmodium falciparum were determined in 229 Gabonese children. HLA class I and II typing (by PCR-SSP and -RFLP, respectively) revealed that HLA-A*19, -B*17 (and -B*70), -DRB1*05, -DQA1*0102, -DQB1*0602 and -DPB1*0402 were the most frequent types or alleles at each locus. The DQB1*0201 and DQB1*0301 alleles were present at a higher frequency among IL-6 and IFN-gamma responders to the LSA-Rep and LSA-CTL peptides, respectively, and a higher proportion of these responders carried A*19 or B*53. The DRB1*06 type was positively related to the IL-10 production in response to the LSA-CTL peptide, and responders presented mainly A*2. The specificity A*10 was negatively associated with the cellular response to the LSA-J peptide. These results suggest a degree of genetic regulation of specific immune responses by HLA-A, operating at the pre-erythrocytic stage of development of P. falciparum in this Central African population.

Variants of Plasmodium falciparum erythrocyte membrane protein 1 expressed by different placental parasites are closely related and adhere to chondroitin sulfate A.

Plasmodium falciparum-infected erythrocytes adhere to syncytiotrophoblast cells lining the placenta via glycosaminoglycans, such as chondroitin sulfate A (CSA) and hyaluronic acid. Adherence of infected erythrocytes to host receptors is mediated by P. falciparum erythrocyte membrane protein-1 (PfEMP-1). A single PfEMP-1 domain (duffy binding-like [DBL]-3, of the gamma sequence class) from laboratory-adapted strains is thought to be responsible for binding to CSA. In this study, DBL-gamma domains expressed by placental P. falciparum isolates were shown to have an affinity to CSA. All parasite populations accumulating in infected placentas express only 1 variant of PfEMP-1, each of which contains a DBL-gamma domain with CSA binding capacities. Furthermore, sequence analysis data provide evidence for antigenic conservation among the DBL-gamma sequences expressed by different placental parasites. This study offers a close reflection of the process of parasite adhesion in the placenta and is crucial to the understanding of the pathogenesis of malaria during pregnancy.

Sulfadoxine-pyrimethamine for the treatment of Plasmodium falciparum malaria in Gabonese children.

Chloroquine can no longer be recommended as the first-line treatment for falciparum malaria in several parts of Africa, given the increasing resistance of Plasmodium falciparum to this drug. The sulfadoxine-pyrimethamine combination (SP) is obviously an alternative candidate, that has already been selected as first-line antimalarial treatment by a few African countries. However, the extent of resistance to SP appears to be highly variable within Africa. Therefore, we investigated the efficacy of SP to treat uncomplicated malaria attacks in children from south-east Gabon. Sixty-six children presenting with a P. falciparum malaria attack were given a standard regimen of SP, and were followed at Days 3, 7, 14, and 21. No RIII response was observed, but relatively high prevalences of RII (18.2%) and RI (12.1%) were present. Moreover, analysis of the clinical outcome according to CDC criteria showed that initial clinical response was lacking in 8.5% of children, and that clinical failure occurred in 9.1%.

Cellular responses to Loa loa experimental infection in mandrills (Mandrillus sphinx) vaccinated with irradiated infective larvae.

In order to shed light on the mechanisms of antifilarial protective immunity, we investigated the course of experimental loaiosis after vaccination in a nonhuman primate host, Mandrillus sphinx. Six vaccinated (V) mandrills received 50 irradiated L3 while six nonvaccinated (NV) received saline solution on days -60, -30 and -15. All animals were challenged with 100 intact L3 (day 0). Parasitological and immunological status were followed for 9 months. Vaccination delayed the appearance and mean peak of microfilaraemia. Five mandrills (Mf-) were never microfilaraemic (one V mandrill) or microfilaraemic on only one occasion (2 V and 2 NV), the other seven having stable microfilaraemia (Mf+). The cytokine response of peripheral blood mononuclear cells to L3 (L3 Ag) was Th2 dominated, while microfilariae (Mf Ag) elicited a Th0-like response. During vaccination, Th2 cytokine production significantly increased in V mandrills against L3 Ag, as well as Mf Ag, whereas Th1 cytokines decreased. On day 60 postinoculation, cellular proliferation was higher in V mandrills in response to L3 and Mf Ags and PHA-L mitogen. At the end of prepatency (on day 130), mandrills with delayed appearance of microfilaraemia exhibited a high, transient IL-2 and IL-4 secretion in response to L3 Ag. Finally, high anti-Mf Th2 cytokine levels characterized Mf-mandrills not only during prepatency, but also (for IL-5) before immunization. However, the presence of a balanced Th1 anti-L3 response during prepatency in the amicrofilaraemic mandrill suggests its importance in protective immunity. Taken together, our data suggest that Th2 cells and also Th1 components of the antifilarial response, especially to larval antigen, may contribute to parasite elimination.

Cytoadherence of Plasmodium falciparum-infected erythrocytes in the human placenta.

In Plasmodium falciparum-parasitized pregnant women, erythrocytes infected by mature stages of the parasite sequester into placental intervillous spaces. The presence of parasites in the placenta causes maternal anaemia and low birth weight of the infant. In-vitro studies suggest placental sequestration may involve the cytoadherence of infected erythrocytes to chondroitin sulphate A (CSA) and/or intercellular adhesion molecule 1 (ICAM-1) expressed by human placental syncytiotrophoblast. We identified P. falciparum receptors expressed on the surface of human syncytiotrophoblast using immunofluorescence of placental biopsies from Cameroon, a malaria-endemic area. In all placentas, a strongly positive staining was observed on the syncytiotrophoblast for CSA, but not for ICAM-1, vascular endothelium cell adhesion molecule-1, E-selectin, nor CD36. The cytoadherence ability of parasites from pregnant women and nonpregnant subjects was assessed on in-vitro cultured syncytiotrophoblast. Parasites from pregnant women bound to the trophoblast via CSA but not ICAM-1. Parasites from nonpregnant hosts either did not bind to the trophoblast culture or bound using ICAM-1. Our data support the idea that placental sequestration may result from cytoadherence to placental trophoblast and that pregnant women are parasitized by parasites that differ from parasites derived from nonpregnant host by their cytoadherence ability.

Human genetic factors related to susceptibility to mild malaria in Gabon.

Several human genetic factors, including red blood cell polymorphisms (ABO blood group, sickle-cell trait, G6PD deficiency) as well as point mutations in the mannose binding protein (MBP) and in the promoter regions of both the TNF-alpha and NOS2 genes, influence the severity of disease due to infection with Plasmodium falciparum. We assessed their impact on mild P. falciparum malaria, as part of a longitudinal investigation of clinical, parasitological and immunological parameters in a cohort of 300 Gabonese schoolchildren. We found the following frequencies: blood group O (0.54), sickle-cell trait (0.23), G6PD deficiency (0.09), MBP gene mutations (0.34), TNF-alpha promoter mutations (at positions -238: 0.17 and -308: 0.22) and NOS2 promoter mutation (0.18). Blood group O or hemoglobin AA were associated with protection against higher parasitemia. Girls with normal G6PD enzyme activity were protected against clinical malaria attacks. In addition, we demonstrated for the first time that the mutation at position -238 of the gene coding for the promoter region of TNF-alpha was positively correlated with the level of the antibody response specific for epitopes of the antigens MSA-2 and RAP-1 of P. falciparum.