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.

Dynamics of Plasmodium falciparum gametocyte carriage in pregnant women under intermittent preventive treatment with sulfadoxine-pyrimethamine in Benin.

BACKGROUND: In sub-Saharan Africa, malaria is a major cause of morbidity and mortality, in particular in children and pregnant women. During pregnancy, Plasmodium falciparum infected red blood cells expressing VAR2CSA are selected from circulation by selective cytoadherence to chondroitin sulfate proteoglycan receptors expressed in the placenta, leading to an increased susceptibility to malaria, long-lasting infections and poor pregnancy outcome. Partly because of these long-lasting infections, women were reported to have a higher density of gametocytes in their peripheral blood, and are considered as a potential reservoir for malaria transmission. To improve pregnancy outcome in areas of high malaria transmission, The WHO recommends intermittent preventive treatment with sulfadoxine/pyrimethamine (IPTp-SP) during antenatal care visits. The effect of IPTp-SP on gametocyte carriage in infected pregnant women was studied. METHODS: The levels of transcription of three gametocytes stage-specific genes Pfs16 (expressed by sexually-committed ring stage parasites and fully matured gametocytes), Pfs25 (expressed by female mature gametocytes) and Pfs230 (expressed by male mature gametocytes) were assessed by real-time PCR in 50 P. falciparum infected women at early pregnancy (before implementation of IPTp-SP), and in 50 infected women at delivery. Sex ratios of male and female gametocytes were determined in these women to assess the effect of IPTp-SP on the gametocyte populations. RESULTS: The data show that the three transcript types specific to Pfs16, Pfs25 and Pfs230 were detected in all samples, both at inclusion and delivery. Levels of Pfs25 and Pfs230 transcripts were higher at delivery than at inclusion (p = 0.042 and p = 0.003), while the opposite was observed for Pfs16 (p = 0.048). The ratio of male/female gametocyte transcript levels was higher at delivery than at inclusion (p = 0.018). Since a mixed gender late stage gametocyte culture was used as a positive control, male and female gametocytes could not be quantified in an absolute way in the samples. However, the amplification reliability of the Pfs25 and Pfs230 markers in the samples could be checked. A relative quantity of each type of Pfs transcript was, therefore, used to calculate the sex ratio proxy. CONCLUSION: This study demonstrates that IPTp-SP treatment contributes to modify the parasite populations' structure during pregnancy. In line with previous studies, we suggest that the continued use of SP in pregnant women as IPTp, despite having a beneficial effect on the pregnancy outcome, could be a risk factor for increased transmission. This reinforces the need for an alternative to the SP drug for malaria prevention during pregnancy.

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.

Comparison of the Performances of Five Primer Sets for the Detection and Quantification of Plasmodium in Anopheline Vectors by Real-Time PCR.

Quantitative real-time polymerase chain reaction (qrtPCR) has made a significant improvement for the detection of Plasmodium in anopheline vectors. A wide variety of primers has been used in different assays, mostly adapted from molecular diagnosis of malaria in human. However, such an adaptation can impact the sensitivity of the PCR. Therefore we compared the sensitivity of five primer sets with different molecular targets on blood stages, sporozoites and oocysts standards of Plasmodium falciparum (Pf) and P. vivax (Pv). Dilution series of standard DNA were used to discriminate between methods at low concentrations of parasite and to generate standard curves suitable for the absolute quantification of Plasmodium sporozoites. Our results showed that the best primers to detect blood stages were not necessarily the best ones to detect sporozoites. Absolute detection threshold of our qrtPCR assay varied between 3.6 and 360 Pv sporozoites and between 6 and 600 Pf sporozoites per mosquito according to the primer set used in the reaction mix. In this paper, we discuss the general performance of each primer set and highlight the need to use efficient detection methods for transmission studies.

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.