Sustained clinical benefit of malaria chemoprevention with sulfadoxine-pyrimethamine (SP) in pregnant women in a region with high SP resistance markers.

OBJECTIVE: The effectiveness of intermittent preventive treatment of malaria in pregnancy with sulfadoxine-pyrimethamine (IPTp-SP) is threatened by increasing SP-resistance in Africa. We assessed the level of SP-resistance markers, and the clinical and parasitological effectiveness of IPTp-SP in southern Mozambique. METHODS: P. falciparum infection, antimalarial antibodies and dhfr/dhps SP-resistance mutants were detected by quantitative polymerase chain reaction (qPCR), suspension array technology and targeted deep sequencing, respectively, among 4016 HIV-negative women in Maputo province (2016-2019). Univariate and multivariate regression models were used to assess the association between taking the recommended three or more IPTp-SP doses (IPTp3+) and parasitological and clinical outcomes. RESULTS: 84.3% (3385/4016) women received three or more IPTp-SP doses. The prevalence of quintuple mutants at first antenatal care (ANC) visit was 94.2%. IPTp3+ was associated with a higher clearance rate of qPCR-detected infections from first ANC visit to delivery (adjusted odds ratio [aOR]=5.9, 95% CI: 1.5-33.3; p = 0.012), lower seroprevalence at delivery of antibodies against the pregnancy-specific antigen VAR2CSADBL34 (aOR=0.72, 95% CI: 0.54-0.95; p = 0.022), and lower prevalence of low birth weight deliveries (aOR: 0.61, 95% CI: 0.41-0.90; p = 0.013). CONCLUSION: A sustained parasitological effect of IPTp-SP contributes to the clinical effectiveness of IPTp3+ in areas with high prevalence of SP-resistance markers.

Targeted and whole-genome sequencing reveal a north-south divide in P. falciparum drug resistance markers and genetic structure in Mozambique

Mozambique is one of the four African countries which account for over half of all malaria deaths worldwide, yet little is known about the parasite genetic structure in that country. We performed P. falciparum amplicon and whole genome sequencing on 2251 malaria-infected blood samples collected in 2015 and 2018 in seven provinces of Mozambique to genotype antimalarial resistance markers and interrogate parasite population structure using genome-wide microhaplotyes. Here we show that the only resistance-associated markers observed at frequencies above 5% were pfmdr1-184F (59%), pfdhfr-51I/59 R/108 N (99%) and pfdhps-437G/540E (89%). The frequency of pfdhfr/pfdhps quintuple mutants associated with sulfadoxine-pyrimethamine resistance increased from 80% in 2015 to 89% in 2018 (p < 0.001), with a lower expected heterozygosity and higher relatedness of microhaplotypes surrounding pfdhps mutants than wild-type parasites suggestive of recent selection. pfdhfr/pfdhps quintuple mutants also increased from 72% in the north to 95% in the south (2018; p < 0.001). This resistance gradient was accompanied by a concentration of mutations at pfdhps-436 (17%) in the north, a south-to-north increase in the genetic complexity of P. falciparum infections (p = 0.001) and a microhaplotype signature of regional differentiation. The parasite population structure identified here offers insights to guide antimalarial interventions and epidemiological surveys.

Determinants of early antibody responses to COVID-19 mRNA vaccines in a cohort of exposed and naïve healthcare workers.

BACKGROUND: Two doses of mRNA vaccination have shown >94% efficacy at preventing COVID-19 mostly in naïve adults, but it is not clear if the second dose is needed to maximize effectiveness in those previously exposed to SARS-CoV-2 and what other factors affect responsiveness. METHODS: We measured IgA, IgG and IgM levels against SARS-CoV-2 spike (S) and nucleocapsid (N) antigens from the wild-type and S from the Alpha, Beta and Gamma variants of concern, after BNT162b2 (Pfizer/BioNTech) or mRNA-1273 (Moderna) vaccination in a cohort of health care workers (N=578). Neutralizing capacity and antibody avidity were evaluated. Data were analyzed in relation to COVID-19 history, comorbidities, vaccine doses, brand and adverse events. FINDINGS: Vaccination induced robust IgA and IgG levels against all S antigens. Neutralization capacity and S IgA and IgG levels were higher in mRNA-1273 vaccinees, previously SARS-CoV-2 exposed, particularly if symptomatic, and in those experiencing systemic adverse effects (p<0·05). A second dose in pre-exposed did not increase antibody levels. Smoking and comorbidities were associated with 43% (95% CI, 19-59) and 45% (95% CI, 63-18) lower neutralization, respectively, and 35% (95% CI, 3-57%) and 55% (95% CI, 33-70%) lower antibody levels, respectively. Among fully vaccinated, 6·3% breakthroughs were detected up to 189 days post-vaccination. Among pre-exposed non-vaccinated, 90% were IgG seropositive more than 300 days post-infection. INTERPRETATION: Our data support administering a single-dose in pre-exposed healthy individuals as primary vaccination. However, heterogeneity of responses suggests that personalized recommendations may be necessary depending on COVID-19 history and life-style. Higher mRNA-1273 immunogenicity would be beneficial for those expected to respond worse to vaccination and in face of variants that escape immunity such as Omicron. Persistence of antibody levels in pre-exposed unvaccinated indicates maintenance of immunity up to one year. FUNDING: This work was supported by Institut de Salut Global de Barcelona (ISGlobal) internal funds, in-kind contributions from Hospital Clínic de Barcelona, the Fundació Privada Daniel Bravo Andreu, and European Institute of Innovation and Technology (EIT) Health (grant number 20877), supported by the European Institute of Innovation and Technology, a body of the European Union receiving support from the H2020 Research and Innovation Programme. We acknowledge support from the Spanish Ministry of Science and Innovation and State Research Agency through the "Centro de Excelencia Severo Ochoa 2019-2023" Program (CEX2018-000806-S), and support from the Generalitat de Catalunya through the CERCA Program. L. I. work was supported by PID2019-110810RB-I00 grant from the Spanish Ministry of Science & Innovation. Development of SARS-CoV-2 reagents was partially supported by the National Institute of Allergy and Infectious Diseases Centers of Excellence for Influenza Research and Surveillance (contract number HHSN272201400008C). The funders had no role in study design, data collection and analysis, the decision to publish, or the preparation of the manuscript.

Highly Sensitive and Specific Multiplex Antibody Assays To Quantify Immunoglobulins M, A, and G against SARS-CoV-2 Antigens.

Reliable serological tests are required to determine the prevalence of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and to characterize immunity to the disease in order to address key knowledge gaps in the coronavirus disease 2019 (COVID-19) pandemic. Quantitative suspension array technology (qSAT) assays based on the xMAP Luminex platform overcome the limitations of rapid diagnostic tests and enzyme-linked immunosorbent assays (ELISAs) with their higher precision, dynamic range, throughput, miniaturization, cost-efficiency, and multiplexing capacity. We developed three qSAT assays for IgM, IgA, and IgG against a panel of eight SARS-CoV-2 antigens, including spike protein (S), nucleocapsid protein (N), and membrane protein (M) constructs. The assays were optimized to minimize the processing time and maximize the signal-to-noise ratio. We evaluated their performances using 128 prepandemic plasma samples (negative controls) and 104 plasma samples from individuals with SARS-CoV-2 diagnosis (positive controls), of whom 5 were asymptomatic, 51 had mild symptoms, and 48 were hospitalized. Preexisting IgG antibodies recognizing N, M, and S proteins were detected in negative controls, which is suggestive of cross-reactivity to common-cold coronaviruses. The best-performing antibody/antigen signatures had specificities of 100% and sensitivities of 95.78% at ≥14 days and 95.65% at ≥21 days since the onset of symptoms, with areas under the curve (AUCs) of 0.977 and 0.999, respectively. Combining multiple markers as assessed by qSAT assays has the highest efficiency, breadth, and versatility to accurately detect low-level antibody responses for obtaining reliable data on the prevalence of exposure to novel pathogens in a population. Our assays will allow gaining insights into antibody correlates of immunity and their kinetics, required for vaccine development to combat the COVID-19 pandemic.

Gametocytes of the Malaria Parasite Plasmodium falciparum Interact With and Stimulate Bone Marrow Mesenchymal Cells to Secrete Angiogenetic Factors.

The gametocytes of Plasmodium falciparum, responsible for the transmission of this malaria parasite from humans to mosquitoes, accumulate and mature preferentially in the human bone marrow. In the 10 day long sexual development of P. falciparum, the immature gametocytes reach and localize in the extravascular compartment of this organ, in contact with several bone marrow stroma cell types, prior to traversing the endothelial lining and re-entering in circulation at maturity. To investigate the host parasite interplay underlying this still obscure process, we developed an in vitro tridimensional co-culture system in a Matrigel scaffold with P. falciparum gametocytes and self-assembling spheroids of human bone marrow mesenchymal cells (hBM-MSCs). Here we show that this co-culture system sustains the full maturation of the gametocytes and that the immature, but not the mature, gametocytes adhere to hBM-MSCs via trypsin-sensitive parasite ligands exposed on the erythrocyte surface. Analysis of a time course of gametocytogenesis in the co-culture system revealed that gametocyte maturation is accompanied by the parasite induced stimulation of hBM-MSCs to secrete a panel of 14 cytokines and growth factors, 13 of which have been described to play a role in angiogenesis. Functional in vitro assays on human bone marrow endothelial cells showed that supernatants from the gametocyte mesenchymal cell co-culture system enhance ability of endothelial cells to form vascular tubes. These results altogether suggest that the interplay between immature gametocytes and hBM-MSCs may induce functional and structural alterations in the endothelial lining of the human bone marrow hosting the P. falciparum transmission stages.

Validity of a minimally invasive autopsy tool for cause of death determination in pediatric deaths in Mozambique: An observational study.

BACKGROUND: In recent decades, the world has witnessed unprecedented progress in child survival. However, our knowledge of what is killing nearly 6 million children annually in low- and middle-income countries remains poor, partly because of the inadequacy and reduced precision of the methods currently utilized in these settings to investigate causes of death (CoDs). The study objective was to validate the use of a minimally invasive autopsy (MIA) approach as an adequate and more acceptable substitute for the complete diagnostic autopsy (CDA) for pediatric CoD investigation in a poor setting. METHODS AND FINDINGS: In this observational study, the validity of the MIA approach in determining the CoD was assessed in 54 post-neonatal pediatric deaths (age range: ≥1 mo to 15 y) in a referral hospital of Mozambique by comparing the results of the MIA with those of the CDA. Concordance in the category of disease obtained by the two methods was evaluated by the Kappa statistic, and the sensitivity, specificity, and positive and negative predictive values of the MIA diagnoses were calculated. A CoD was identified in all cases in the CDA and in 52/54 (96%) of the cases in the MIA, with infections and malignant tumors accounting for the majority of diagnoses. The MIA categorization of disease showed a substantial concordance with the CDA categorization (Kappa = 0.70, 95% CI 0.49-0.92), and sensitivity, specificity, and overall accuracy were high. The ICD-10 diagnoses were coincident in up to 75% (36/48) of the cases. The MIA allowed the identification of the specific pathogen deemed responsible for the death in two-thirds (21/32; 66%) of all deaths of infectious origin. Discrepancies between the MIA and the CDA in individual diagnoses could be minimized with the addition of some basic clinical information such as those ascertainable through a verbal autopsy or clinical record. The main limitation of the analysis is that both the MIA and the CDA include some degree of expert subjective interpretation. CONCLUSIONS: The MIA showed substantial concordance with CDA for CoD identification in this series of pediatric deaths in Mozambique. This minimally invasive approach, simpler and more readily acceptable than the more invasive CDA, could provide robust data for CoD surveillance, especially in resource-limited settings, which could be helpful for guiding child survival strategies in the future.

A humanized mouse model for sequestration of Plasmodium falciparum sexual stages and in vivo evaluation of gametocytidal drugs.

The development of new drugs to disrupt malaria transmission requires the establishment of an in vivo model to address the biology of Plasmodium falciparum sexual stages (gametocytes). Herein we show that chemically immune-modulated NSG mice grafted with human erythrocytes support complete sexual development of P. falciparum parasites and generate high gametocytemia. Immunohistochemistry and RT-qPCR analyses indicate an enrichment of immature gametocytes in the bone marrow and the spleen, suggesting a sequestration mechanism reminiscent to that observed in humans. Upon primaquine treatment, elimination of gametocytes from peripheral blood and from sequestration sites was observed, providing a proof of concept that these mice can be used for testing drugs. Therefore, this model allows the investigation of P. falciparum sexual commitment, gametocyte interactions with the bone marrow and spleen and provides the missing link between current in vitro assays and Phase I trials in humans for testing new malaria gametocytidal drugs.

Pregnancy and malaria exposure are associated with changes in the B cell pool and in plasma eotaxin levels.

Pregnancy triggers immunological changes aimed to tolerate the fetus, but its impact on B lymphocytes is poorly understood. In addition, exposure to the Plasmodium parasite is associated with altered distribution of peripheral memory B cell (MBC) subsets. To study the combined impact of high malaria exposure and pregnancy in B cell subpopulations, we analyzed PBMCs from pregnant and nonpregnant individuals from a malaria-nonendemic country (Spain) and from a high malaria-endemic country (Papua New Guinea). In the malaria-naive cohorts, pregnancy was associated with a significant expansion of all switched (IgD(-)) MBC and a decrease of naive B cells. Malaria-exposed women had more atypical MBC and fewer marginal zone-like MBC, and their levels correlated with both Plasmodium vivax- and Plasmodium falciparum-specific plasma IgG levels. Classical but not atypical MBC were increased in P. falciparum infections. Moreover, active atypical MBC positively correlated with proinflammatory cytokine plasma concentrations and had lower surface IgG levels than the average. Decreased plasma eotaxin (CCL11) levels were associated with pregnancy and malaria exposure and also correlated with B cell subset frequencies. Additionally, active atypical and active classical MBC expressed higher levels of eotaxin receptor CCR3 than the other B cell subsets, suggesting a chemotactic effect of eotaxin on these B cell subsets. These findings are important to understand immunity to infections like malaria that result in negative outcomes for both the mother and the newborn and may have important implications on vaccine development.

Impact of age of first exposure to Plasmodium falciparum on antibody responses to malaria in children: a randomized, controlled trial in Mozambique.

BACKGROUND: The impact of the age of first Plasmodium falciparum infection on the rate of acquisition of immunity to malaria and on the immune correlates of protection has proven difficult to elucidate. A randomized, double-blind, placebo-controlled trial using monthly chemoprophylaxis with sulphadoxine-pyrimethamine plus artesunate was conducted to modify the age of first P. falciparum erythrocytic exposure in infancy and assess antibodies and malaria risk over two years. METHODS: Participants (n = 349) were enrolled at birth to one of three groups: late exposure, early exposure and control group, and were followed up for malaria morbidity and immunological analyses at birth, 2.5, 5.5, 10.5, 15 and 24 months of age. Total IgG, IgG subclasses and IgM responses to MSP-1(19), AMA-1, and EBA-175 were measured by ELISA, and IgG against variant antigens on the surface of infected erythrocytes by flow cytometry. Factors affecting antibody responses in relation to chemoprophylaxis and malaria incidence were evaluated. RESULTS: Generally, antibody responses did not vary significantly between exposure groups except for levels of IgM to EBA-175, and seropositivity of IgG1 and IgG3 to MSP-1(19). Previous and current malaria infections were strongly associated with increased IgG against MSP-1(19), EBA-175 and AMA-1 (p < 0.0001). After adjusting for exposure, only higher levels of anti-EBA-175 IgG were significantly associated with reduced clinical malaria incidence (IRR 0.67, p = 0.0178). CONCLUSIONS: Overall, the age of first P. falciparum infection did not influence the magnitude and breadth of IgG responses, but previous exposure was critical for antibody acquisition. IgG responses to EBA-175 were the strongest correlate of protection against clinical malaria. TRIAL REGISTRATION: ClinicalTrials.gov: NCT00231452.

Severity of anaemia is associated with bone marrow haemozoin in children exposed to Plasmodium falciparum.

There are no large-scale ex vivo studies addressing the contribution of Plasmodium falciparum in the bone marrow to anaemia. The presence of malaria parasites and haemozoin were studied in bone marrows from 290 anaemic children attending a rural hospital in Mozambique. Peripheral blood infections were determined by microscopy and polymerase chain reactions. Bone marrow parasitaemia, haemozoin and dyserythropoiesis were microscopically assessed. Forty-two percent (123/290) of children had parasites in the bone marrow and 49% (111/226) had haemozoin, overlapping with parasitaemia in 83% (92/111) of cases. Sexual and mature asexual parasites were highly prevalent (62% gametocytes, 71% trophozoites, 23% schizonts) suggesting their sequestration in this tissue. Sixteen percent (19/120) of children without peripheral infection had haemozoin in the bone marrow. Haemozoin in the bone marrow was independently associated with decreased Hb concentration (P = 0·005) and was more common in dyserythropoietic bone marrows (P = 0·010). The results of this ex vivo study suggest that haemozoin in the bone marrow has a role in the pathogenesis of malarial-anaemia through ineffective erythropoiesis. This finding may have clinical implications for the development of drugs targeted to prevent and treat malarial-anaemia.

Molecular evidence for the localization of Plasmodium falciparum immature gametocytes in bone marrow.

Plasmodium falciparum immature gametocytes are not observed in peripheral blood. However, gametocyte stages in organs such as bone marrow have never been assessed by molecular techniques, which are more sensitive than optical microscopy. We quantified P falciparum sexual stages in bone marrow (n = 174) and peripheral blood (n = 70) of Mozambican anemic children by quantitative polymerase chain reaction targeting transcripts specific for early (PF14_0748; PHISTa), intermediate (PF13_0247; Pfs48/45), and mature (PF10_0303; Pfs25) gametocytes. Among children positive for the P falciparum housekeeping gene (PF08_0085; ubiquitin-conjugating enzyme gene) in bone marrow (n = 136) and peripheral blood (n = 25), prevalence of immature gametocytes was higher in bone marrow than peripheral blood (early: 95% vs 20%, P < .001; intermediate: 80% vs 16%; P < .001), as were transcript levels (P < .001 for both stages). In contrast, mature gametocytes were more prevalent (100% vs 51%, P < .001) and abundant (P < .001) in peripheral blood than in the bone marrow. Severe anemia (3.57, 95% confidence interval 1.49-8.53) and dyserythropoiesis (6.21, 95% confidence interval 2.24-17.25) were independently associated with a higher prevalence of mature gametocytes in bone marrow. Our results highlight the high prevalence and abundance of early sexual stages in bone marrow, as well as the relationship between hematological disturbances and gametocyte development in this tissue.

Placental infection with Plasmodium vivax: a histopathological and molecular study.

BACKGROUND: Evidence of the presence of Plasmodium vivax in the placenta is scarce and inconclusive. This information is relevant to understanding whether P. vivax affects placental function and how it may contribute to poor pregnancy outcomes. METHODS: Histopathologic examination of placental biopsies from 80 Papua New Guinean pregnant women was combined with quantitative polymerase chain reaction (qPCR) to confirm P. vivax infection and rule out coinfection with other Plasmodium species in placental and peripheral blood. Leukocytes and monocytes/macrophages were detected in placental sections by immunohistochemistry. RESULTS: Monoinfection by P. vivax and Plasmodium falciparum was detected by qPCR in 8 and 10 placentas, respectively. Seven of the 8 women with P. vivax placental monoinfection were negative in peripheral blood. By histology, 3 placentas with P. vivax monoinfection showed parasitized erythrocytes in the intervillous space but no hemozoin in macrophages nor increased intervillous inflammatory cells. In contrast, 7 placentas positive for P. falciparum presented parasites and hemozoin in macrophages or fibrin as well as intervillous inflammatory infiltrates. CONCLUSIONS: Plasmodium vivax can be associated with placental infection. However, placental inflammation is not observed in P. vivax monoinfections, suggesting other causes of poor delivery outcomes associated with P. vivax infection.

The role of age and exposure to Plasmodium falciparum in the rate of acquisition of naturally acquired immunity: a randomized controlled trial.

BACKGROUND: The rate of acquisition of naturally acquired immunity (NAI) against malaria predominantly depends on transmission intensity and age, although disentangling the effects of these is difficult. We used chemoprophylaxis to selectively control exposure to P. falciparum during different periods in infancy and explore the effect of age in the build-up of NAI, measured as risk of clinical malaria. METHODS AND FINDINGS: A three-arm double-blind randomized placebo-controlled trial was conducted in 349 infants born to Mozambican HIV-negative women. The late exposure group (LEG) received monthly Sulfadoxine-Pyrimethamine (SP) plus Artesunate (AS) from 2.5-4.5 months of age and monthly placebo from 5.5-9.5 months; the early exposure group (EEG) received placebo from 2.5-4.5 months and SP+AS from 5.5-9.5 months; and the control group (CG) received placebo from 2.5-9.5 months. Active and passive case detection (PCD) were conducted from birth to 10.5 and 24 months respectively. The primary endpoint was time to first or only episode of malaria in the second year detected by PCD. The incidence of malaria during the second year was of 0.50, 0.51 and 0.35 episodes/PYAR in the LEG, EEG and CG respectively (p = 0.379 for the adjusted comparison of the 3 groups). The hazard ratio of the adjusted comparison between the LEG and the CG was 1.38 (0.83-2.28, p = 0.642) and that between the EEG and the CG was 1.35 (0.81-2.24, p = 0.743). CONCLUSIONS: After considerably interfering with exposure during the first year of life, there was a trend towards a higher risk of malaria in the second year in children who had received chemoprophylaxis, but there was no significant rebound. No evidence was found that the age of first exposure to malaria affects the rate of acquisition of NAI. Thus, the timing of administration of antimalarial interventions like malaria vaccines during infancy does not appear to be a critical determinant. TRIAL REGISTRATION: ClinicalTrials.gov NCT00231452.

HIV and malaria interactions: where do we stand?

Reversing the spread of HIV infection and the incidence of malaria constitute two of the Millenium Development Goals. However, despite recent achievements, both diseases still entail global heath problems. Furthermore, their overlapping geographical distribution raises concerns and challenges for potential immunological, clinical and therapeutic interactions. It has been reported that HIV infection increases malaria susceptibility and reduces the efficacy of antimalarial drugs. On the other hand, the effect of malaria on HIV-infected individuals has also been explored, with the parasitic infection increasing the risk of HIV disease progression and mother-to-child transmission of HIV. The spread of malaria and parasite resistance to antimalarials could also be accelerated by HIV-associated immunosuppresion. Current knowledge of the epidemiological, clinical, immunological and therapeutic interactions of the two diseases is reviewed in this article. We focus on the latest available data, pointing out key future research areas and challenges of the field.

HIV and placental infection modulate the appearance of drug-resistant Plasmodium falciparum in pregnant women who receive intermittent preventive treatment.

BACKGROUND: Factors involved in the development of resistance to sulphadoxine-pyrimethamine (SP) by Plasmodium falciparum, particularly in the context of intermittent preventive treatment during pregnancy (IPTp), are not well known. We aimed to determine the impact of IPTp and human immunodeficiency virus (HIV) infection on molecular markers of SP resistance and the clinical relevance of resistant infections. METHODS: SP resistance alleles were determined in peripheral (n = 125) and placental (n = 145) P. falciparum isolates obtained from pregnant women enrolled in a randomized, placebo-controlled trial of IPTp in Manhiça, Mozambique. RESULTS: Prevalence of quintuple mutant infections was 12% (23 of 185 isolates) in pregnant women who received placebo and 24% (20 of 85 isolates) in those who received SP (P = .031). When the last IPTp dose was administered at late pregnancy, mutant infections at delivery were more prevalent in placental samples (7 [23%] of 30, samples) than in peripheral blood samples (2 [7%] of 30 samples; P = .025), more prevalent in women who received IPTp-SP than in those who received placebo (odds ratio [OR], 8.13; 95% confidence interval [CI], 1.69-39.08), and more prevalent in HIV-positive women than in HIV-negative women (OR, 5.17; 95% CI, 1.23-21.66). No association was found between mutant infections and increased parasite density or malaria-related morbidity in mothers and children. CONCLUSIONS: IPTp with SP increases the prevalence of resistance markers in the placenta and in HIV-infected women at delivery, which suggests that host immunity is key for the clearance of drug-resistant infections. However, this effect of IPTp is limited to the period when blood levels of SP are likely to be significant and does not translate into more-severe infections or adverse clinical outcomes.

The effect of intermittent preventive treatment during pregnancy on malarial antibodies depends on HIV status and is not associated with poor delivery outcomes.

BACKGROUND: Intermittent preventive treatment during pregnancy (IPTp) with sulfadoxine-pyrimethamine (SP) is recommended for malaria prevention in sub-Saharan Africa. However, studies reporting the effect of IPTp on malaria-specific immunity are scarce and are based on findings in human immunodeficiency virus (HIV)-negative primigravidae. METHODS: Plasma samples obtained from 302 pregnant women (177 who were HIV negative, 88 who were HIV positive, and 37 who were of unknown HIV status) participating in a placebo-controlled trial of IPTp with SP (IPTp-SP) were analyzed for the presence of antibodies against merozoite antigens, whole asexual parasites, and variant surface antigens from chondroitin sulfate A-binding and nonbinding lines. Antibody levels were compared between intervention groups, and their association with morbidity outcomes was assessed. RESULTS: HIV-positive mothers receiving SP had lower levels of peripheral antibodies against apical membrane antigen-1 and variant surface antigens, as well as lower levels of cord antibodies against erythrocyte-binding antigen-175 and parasite lysate, than did HIV-positive placebo recipients. No difference between intervention groups was observed among HIV-negative mothers. High antibody levels were associated with maternal infection and an increased risk of a first malaria episode in infants. Antibody responses were not consistently associated with reduced maternal anemia, prematurity, or low birth weight. CONCLUSIONS: The IPTp-associated reduction in antibodies in HIV-infected women, but not in HIV-uninfected women, may reflect a higher efficacy of the intervention in preventing malaria among HIV-positive mothers. This reduction did not translate into an enhanced risk of malaria-associated morbidity in mothers and infants. Trial registration. Clinicaltrials.gov identifier NCT00209781.

Receptor-binding residues lie in central regions of Duffy-binding-like domains involved in red cell invasion and cytoadherence by malaria parasites.

Erythrocyte invasion by malaria parasites and cytoadherence of Plasmodium falciparum-infected erythrocytes to host capillaries are 2 key pathogenic mechanisms in malaria. The receptor-binding domains of erythrocyte-binding proteins (EBPs) such as Plasmodium falciparum EBA-175, which mediate invasion, and P falciparum erythrocyte membrane protein 1 (PfEMP-1) family members, which are encoded by var genes and mediate cytoadherence, have been mapped to conserved cysteine-rich domains referred to as Duffy-binding-like (DBL) domains. Here, we have mapped regions within DBL domains from EBPs and PfEMP-1 that contain receptor-binding residues. Using biochemical and molecular methods we demonstrate that the receptor-binding residues of parasite ligands that bind sialic acid on glycophorin A for invasion as well as complement receptor-1 and chondroitin sulfate A for cytoadherence map to central regions of DBL domains. In contrast, binding to intercellular adhesion molecule 1 (ICAM-1) requires both the central and terminal regions of DBLbetaC2 domains. Determination of functional regions within DBL domains is the first step toward understanding the structure-function bases for their interaction with diverse host receptors.