Progression of stunting and its predictors among school-aged children in western Kenya.

OBJECTIVE: The objectives of this study were (1) to assess whether a cohort of school-aged children experiences progression of stunting over a 2-y-period of observation and (2) to identify baseline nutritional and body composition risk factors for the progression of stunting. METHODS: As part of a large-scale, randomized controlled trial assessing the impact of insecticide-treated bednets (ITNs) on nutritional status, we longitudinally followed a cohort of school-aged children over a 2-y-period in western Kenya. Anthropometric measurements were made at four time points from which Z-scores for height-for-age (HAZ), weight-for-age (WAZ), and body mass index (BMIZ) were calculated. Two measures of body composition, upper arm fat area and upper arm muscle area, were derived from mid-upper arm circumference (MUAC) and triceps skinfold thickness. RESULTS: Subjects experienced a mean change in HAZ from baseline to 9 months of -0.16 [-0.19, -0.13], from baseline to 16 months of -0.18 [-0.22, -0.15], and from baseline to 24 months of -0.36 [-0.41, -0.31]. Thus, the average individual's change in HAZ at the three follow-up time points is significantly less than zero, meaning that, on average, the cohort is deviating further from NCHS reference medians over time. The baseline nutritional measure that explained the greatest amount of variance in the progression of stunting was the upper arm muscle area Z-score (F=8.1; P=0.005). CONCLUSIONS: This longitudinal study provides further evidence from a distinct ecological setting regarding the progression of undernutrition during middle childhood in the developing world. It suggests that school-aged children in the developing world do not experience catch-up growth or remain stable. Rather, they continue to deviate from NCHS standards, accruing greater height deficits with age. In addition, absolute lean body mass explained the most variability in the progression of stunting, which supports cross-sectional findings from other studies.

Monitoring trends in under-5 mortality rates through national birth history surveys.

BACKGROUND: We assessed whether Demographic and Health Surveys (DHS), a large and high-quality source of under-5 mortality estimates in developing countries, would be able to detect reductions in under-5 mortality as established in global child health goals. METHODS AND RESULTS: Mortality estimates from 41 DHS conducted in African countries between 1986 and 2002, for the interval of 0-4 years preceding each survey (with a mean time lag of 2.5 years), were reviewed. The median relative error on national mortality rates was 4.4%. In multivariate regression, the relative error decreased with increasing sample size, increasing fertility rates, and increasing mortality rates. The error increased with the magnitude of the survey design effect, which resulted from cluster sampling. With levels of precision observed in previous surveys, reductions in all-cause under-5 mortality rates between two subsequent surveys of 15% or more would be detectable. The detection of smaller mortality reductions would require increases in sample size, from a current median of 7060 to over 20,000 women. Across the actual surveys conducted between 1986 and 2002, varying mortality trends were apparent at a national scale, but only around half of these were statistically significant. CONCLUSIONS: The interpretation of changes in under-5 mortality rates between subsequent surveys needs to take into account statistical significance. DHS birth history surveys with their present sampling design would be able to statistically confirm under-5 mortality reductions in African countries if true reductions were 15% or larger, and are highly relevant to tracking progress towards existing international child health targets.

Effectiveness of intermittent preventive treatment with sulphadoxine-pyrimethamine for control of malaria in pregnancy in western Kenya: a hospital-based study.

OBJECTIVE: To monitor the effectiveness of intermittent preventive treatment (IPT) with sulphadoxine-pyrimethamine (SP) for the control of malaria in pregnancy at delivery in the Provincial Hospital in Kisumu, Kenya, and to assess the effect of IPT in participants in a cohort study. METHODS: Between June 1999 and June 2000, information on IPT and birth outcome was collected in 2302 consecutive deliveries. A group of 889 women, who were enrolled in a cohort to assess the interaction between malaria and HIV, were analysed separately because of the enrollment criteria and different access to health care. RESULTS: The prevalence of placental malaria was 13.8% and of low birthweight (LBW) was 12.2%. In multivariable analysis, IPT (> or =1 dose of SP) was associated with a reduction in placental malaria and LBW [adjusted odds ratio (OR) 0.56, 95% confidence interval (CI) 0.39-0.83 and OR 0.65, 95% CI 0.45-0.95, respectively]. An adjusted mean increase in birthweight of 61 g was seen (95% CI 22-101 g) for each increment in number of SP doses (> or =2 doses grouped together). IPT was associated with a reduction in placental malaria in HIV-seronegative women (OR 0.49, 95% CI 0.28-0.86) but this was not significant among HIV-seropositive women (OR 0.45, 95% CI 0.20-1.05). A significant effect on birthweight could not be detected among participants in the HIV-cohort. CONCLUSIONS: This evaluation confirms that IPT with SP is effective in reducing placental malaria and LBW. It will be important to increase coverage of IPT and to extend IPT to antenatal clinics in peri-urban and rural areas.

Comparative flow cytometric analysis of term placental intervillous and peripheral blood from immediate postpartum women in Western kenya.

Understanding maternal immune responses in the placenta is critical for management of pregnancy failures and haematogenous infections during pregnancy. However, it is unknown whether maternal placental intervillous blood (IVB) mononuclear cell populations are distinct from those found in maternal peripheral blood (PB). In this study, cell populations in the IVB and PB from immediate postpartum women were compared by flow cytometry. While levels of B and CD4+ and CD8+ T lymphocytes were similar, IVB contained significantly higher levels of monocytes (10.9+/-5.9 versus 5.5+/-2.5 per cent, respectively) and natural killer cells (14.3+/-9.6 versus 5.9+/-3.2 per cent, respectively) than the PB. Expression of the early activation marker CD69 was increased on T cells in the IVB, whereas levels of HLA-DR, a late activation marker, were similar between IVB and PB. These results suggest that maternal cells that circulate through the intervillous compartment may be subject to local influences that affect their distribution, phenotype and function. Further comparative study of these blood compartments will be necessary to elucidate the mechanisms by which the local placental milieu influences the IVB.

Does infection with Human Immunodeficiency Virus affect the antibody responses to Plasmodium falciparum antigenic determinants in asymptomatic pregnant women?

OBJECTIVES: HIV-seropositive pregnant women are more susceptible to malaria than HIV-seronegative women. We assessed whether HIV infection alters maternal and cord plasma malarial antibody responses and the mother-to-infant transfer of malaria antibodies. METHODS: We determined plasma levels of maternal and cord antibodies [Immunoglobulin (IgG)] to recombinant malarial proteins [merozoite surface protein 1 (MSP-1(19kD)), the erythrocyte binding antigen (EBA-175)], the synthetic peptides [MSP-2, MSP-3, rhoptry associated protein 1 (RAP-1), and the pre-erythrocytic stage, circumsporozoite protein (NANP)(5)] antigenic determinants of Plasmodium falciparum; and tetanus toxoid (TT) by ELISA among samples of 99 HIV-seropositive mothers, 69 of their infants, 102 HIV-seronegative mothers and 62 of their infants. RESULTS: The prevalence of maternal antibodies to the malarial antigenic determinants ranged from 18% on MSP3 to 91% on EBA-175; in cord plasma it ranged from 13% to 91%, respectively. More than 97% of maternal and cord samples had antibodies to TT. In multivariate analysis, HIV infection was only associated with reduced antibodies to (NANP)(5) in maternal (P=0.001) and cord plasma (P=0.001); and reduced mother-to-infant antibody transfer to (NANP)(5) (P=0.012). This effect of HIV was independent of maternal age, gravidity and placental malaria. No consistent HIV-associated differences were observed for other antigenic determinants. CONCLUSION: An effect of HIV infection was only observed on one malarial antigenic determinant, suggesting that the increased susceptibility to malaria among HIV-infected pregnant women may not be explained on the basis of their reduced antibody response to malaria antigens.

Recognition of pallor associated with severe anaemia by primary caregivers in western Kenya.

OBJECTIVES: To explore which pallor signs and symptoms of severe anaemia could be recognized by primary caregivers following minimal instructions. METHODS: Data from three community-based cross-sectional surveys were used. Test characteristics to predict haemoglobin (Hb) concentrations < 5 and < 7 g/dl were compared for different combinations of pallor signs (eyelid, tongue, palmar and nailbed) and symptoms. RESULTS: Pallor signs and haemoglobin levels were available for 3782 children under 5 years of age from 2609 households. Comparisons of the sensitivity and specificity at a range of haemoglobin cut-offs showed that Hb < 5 g/dl was associated with the greatest combined sensitivity and specificity for pallor at any anatomical site (sensitivity = 75.6%, specificity = 63.0%, Youden index = 38.6). Higher or lower haemoglobin cut-offs resulted in more children being misclassified. Similar results were obtained for all individual pallor sites. Combining a history of soil eating with pallor at any site improved the sensitivity (87.8%) to detect Hb < 5 g/dl with a smaller reduction in specificity (53.3%; Youden index 41.1). Other combinations including respiratory signs or poor feeding resulted in lower accuracy. CONCLUSION: Primary caregivers can recognize severe anaemia (Hb < 5 g/dl) in their children, but only with moderate accuracy. Soil eating should be considered as an additional indicator of severe anaemia. The effect of training caretakers to improve recognition of severe anaemia and care-seeking behaviour at the household level should be assessed in prospective community-based studies.

Antibody responses to repetitive epitopes of the circumsporozoite protein, liver stage antigen-1, and merozoite surface protein-2 in infants residing in a Plasmodium falciparum-hyperendemic area of western Kenya. XIII. Asembo Bay Cohort Project.

The present study was initiated to characterize antibody responses to repetitive epitopes of the circumsporozoite protein (CSP), liver stage antigen-1 (LSA-1), and merozoite surface protein-2 (MSP-2) of Plasmodium falciparum in infants residing in a P. falciparum-hyperendemic area of western Kenya. In this study, development and maintenance of these antibody responses in 28 infants were studied longitudinally by use of monthly serum samples collected from birth to age 1 year. Mother plasma and infant umbilical cord plasma were also tested to assess the transplacental transfer of maternal antibodies. Results showed that antibodies passively transferred from mothers were detectable for CSP, LSA-1, and MSP-2 repeat epitopes. Infants were able to mount and maintain a strong antibody response against LSA-1 in their first year of life. Infants often responded to CSP repeats, but with a much lower antibody titer. Antibody responses in infants against Fc27 and 3D7 repeats of MSP-2 were low throughout their first year. In addition, 51 infants whose first detected infection occurred at > 4 months of age were selected to determine antibody responses to the antigens tested upon their first and second detected infections. Antibody responses to LSA-1 and, to a lesser degree, CSP increased in positivity rates and titer upon second infection. Antibody responses to Fc27-type and 3D7-type repeats of MSP-2 were low upon both infections. There was no association between maternally transferred anti-LSA-1, anti-CSP, or anti-MSP-2 antibodies and an infant's first detected infection. No significant correlation was found between an infant's antibody responses to the 4 antigen repetitive epitopes and protection against malarial parasitemia during the first year of life.

Plasmodium falciparum genotypes, low complexity of infection, and resistance to subsequent malaria in participants in the Asembo Bay Cohort Project.

To assess the relationship between the within-host diversity of malaria infections and the susceptibility of the host to subsequent infection, we genotyped 60 children's successive infections from birth through 3 years of life. MSP-1 Block2 genotypes were used to estimate the complexity of infection (COI). Malaria transmission and age were positively associated with the number of K1 and Mad20 alleles detected (COI(KM)) (P < 0.003). Controlling for previous parasitemia, transmission, drug treatment, parasite density, sickle cell, and age, COI(KM) was negatively correlated with resistance to parasitemia of > 500/microl (P < 0.0001). Parasitemias with the RO-genotype were more resistant than those without this genotype (P < 0.0000). The resistance in low COI(KM) infections was not genotype specific. We discuss the impact of genotype-transcending immunity to conserved antigenic determinants. We also propose a diversity-driven immunomodulation hypothesis that may explain the delayed development of natural immunity in the first few years of life and suggest that interventions that decrease the COI(KM) could facilitate the development of protective immunity.

Human immunodeficiency virus seropositivity and malaria as risk factors for third-trimester anemia in asymptomatic pregnant women in western Kenya.

To assess risk factors for anemia in late pregnancy, we studied healthy pregnant women with a singleton uncomplicated pregnancy of > or = 32 weeks attending the prenatal clinic in the Provincial Hospital in Kisumu, Kenya. Between June 1996 and December 1998, 4,608 pregnant women had a blood sample collected for hemoglobin (Hb) measurement, malaria smear, and testing for human immunodeficiency virus (HIV). The mean +/- standard deviation of Hb was 9.58 +/- 1.8 g/dL; 21% had malaria in their blood; and 25% of the women were HIV seropositive. Plasmodium falciparum parasitemia was more common among HIV-seropositive women in all gravidities compared with HIV-seronegative women (risk ratio, 1.71; 95% confidence interval, 1.53-1.92). In a multivariate analysis, for primi- and secundigravidae women, the factors malaria, belonging to the Luo tribe, and HIV seropositivity were significantly associated with any anemia (Hb < 11 g/dL), and HIV seropositivity and documented fever were associated with severe anemia (Hb < 7 g/dL). In women of higher gravidities, HIV seropositivity was the only statistically significant factor associated with any anemia or with severe anemia. Asymptomatic HIV seropositivity is an important risk factor to be considered in the differential diagnosis of maternal anemia, independent of P. falciparum parasitemia.

Tumor necrosis factor-alpha promoter variant 2 (TNF2) is associated with pre-term delivery, infant mortality, and malaria morbidity in western Kenya: Asembo Bay Cohort Project IX.

A polymorphism in the promoter region of the tumor necrosis factor-alpha (TNF-alpha) gene, with a guanine to adenine nucleotide change at position -308, TNF2 is associated with increased TNF-alpha production. TNF2 homozygotes have a higher risk of severe disease and/or death due to cerebral malaria and other infectious diseases. We investigated the impact of this allele on malaria morbidity and mortality in young children who participated in an immuno-epidemiologic cohort study of malaria in an area of intense perennial Plasmodium falciparum transmission in western Kenya. A total of 1,048 children were genotyped. Poisson regression and Cox proportional hazards models were used to determine the relationship between TNF-308 variants and morbidity and mortality. The gene frequencies of the TNF1 and TNF2 alleles were 0.90 and 0.10, respectively. TNF2 homozygosity was associated with pre-term birth when compared with TNF1 homozygotes [relative risk (RR) 7.3, 95% CI, 2.85-18.9, P = 0.002) and heterozygotes (RR 6.7, 95% CI 2.0-23.0, P = 0.008). Among children born prematurely, the TNF2 allele was significantly associated with a higher risk of death in infancy compared with TNF1 (RR 7.47, 95% CI 2.36-23.6). The risk of death was higher among TNF2 homozygotes than among heterozygotes. The TNF2 allele was significantly associated with high density P. falciparum parasitemia (RR 1.11, 95% CI 1.0-1.24). Among low birth weight children, the TNF2 allele was associated with severe anemia (RR 2.16, 95% CI 1.17-4.01) and showed a trend toward a risk for severe malaria anemia (RR 1.99, 95% CI 0.89-4.46). These data suggest that TNF2 is a risk factor for pre-term birth and early childhood mortality and malaria morbidity in children in this region. Further understanding of the pathogenic mechanisms underlying this association is required.

Estimated risk of HIV transmission by blood transfusion in Kenya.

BACKGROUND: During the past decade, developing countries have received limited support for blood safety programmes. The Kenya Ministry of Health did a collaborative multicentre assessment to establish the risk of HIV transmission by transfusion in Kenya, to promote awareness of blood safety issues in this country with a mature HIV epidemic, and to identify methods to reduce the risk of HIV transmission by blood transfusion in Kenya. METHODS: For 12 weeks, from April to July 1994, we collected information and blood samples from all blood donors, and pretransfusion samples were collected from all recipients in six government hospitals in Kenya. Blood donations were collected and screened for HIV according to standard practice in the hospital laboratories. Test results at a reference laboratory were compared with those of the hospital laboratories and risk of transfusion-associated HIV transmission was calculated. FINDINGS: The prevalence of HIV among blood donors was 6.4% (120 of 1877) and varied by hospital (range 2-20%). HIV test results were available for 1290 donor-recipient pairs. Of these, 26 HIV-positive donations were given to HIV-negative patients. We estimate that 2.0% of transfusions transmitted HIV. Problems in the hospitals that contributed to transfusion risk included inconsistent refrigeration, data entry errors, equipment failure, and lack of a quality-assurance programme. INTERPRETATION: A high proportion of blood transfusions transmitted HIV in this high-prevalence area of Africa, primarily because of erroneous laboratory practices. On the basis of these results, the Kenya Ministry of Health introduced a number of practical and inexpensive interventions to improve national blood safety.

Longitudinal study of natural immune responses to the Plasmodium falciparum apical membrane antigen (AMA-1) in a holoendemic region of malaria in western Kenya: Asembo Bay Cohort Project VIII.

We investigated the development and maintenance of proliferative and antibody responses to apical membrane antigen-1 (AMA-1) epitopes in a holoendemic area of western Kenya. Young children (< 10 years), older children (10-17 years), and adults (> or = 18 years) were followed longitudinally for antibody and T-cell responses at 3 time points with an interval of 3-4 months. The proliferative responses against the AMA-1 T epitopes (PL171, PL172, PL173, PL186, PL191, and PL192) were not stable during follow-up; however, response to mycobacterial antigen PPD was highly stable. The responder frequencies were similar in all 3 time points except for epitope PL192. The younger and older children responded more frequently to T-cell epitopes, but the differences were not significant. A positive proliferative response to PL191 was associated with a significantly lower risk of parasitemia at subsequent follow-up (relative risk, 0.5; P = 0.03). The presence of antibody response to B epitopes PL169, PL170, PL173, PL187, and PL192 in one time point was associated with a subsequent response (P = 0.0001-0.008) suggesting a stable response. Younger (P = 0.046) and older children (P = 0.017) more frequently responded to epitope PL169 than did adults, and adults responded more frequently to PL187 than did younger children (P = 0.009). Responses to AMA-1 T-cell epitopes were short lived, and antibody responses were relatively stable.

Cost-effectiveness of sulfadoxine-pyrimethamine for the prevention of malaria-associated low birth weight.

Prevention of placental malaria through administration of antimalarial medications to pregnant women in disease-endemic areas decreases the risk of delivery of low birth weight (LBW) infants. In areas of high Plasmodium falciparum transmission, two intermittent presumptive treatment doses of sulfadoxine-pyrimethamine (SP) during the second and third trimesters of pregnancy are effective in decreasing the prevalence of placental malaria in human immunodeficiency virus (HlV)-negative women, while HIV-positive women may require a monthly SP regimen to reduce their prevalence of placental parasitemia. A decision-analysis model was used to compare the cost-effectiveness of three different presumptive SP treatment regimens with febrile case management with SP in terms of incremental cost per case LBW prevented. Factors considered included HIV seroprevalence, placental malaria prevalence, LBW incidence, the cost of SP, medical care for LBW infants, and HIV testing. For a hypothetical cohort of 10,000 pregnant women, the monthly SP regimen would always be the most effective strategy for reducing LBW associated with malaria. The two-dose SP and monthly SP regimens would prevent 172 and 229 cases of LBW, respectively, compared with the case management approach. At HIV seroprevalence rates greater than 10%, the monthly SP regimen is the least expensive strategy. At HIV seroprevalence rates less than 10%, the two-dose SP regimen would be the less expensive option. When only antenatal clinic costs are considered, the two-dose and monthly SP strategies cost US $11 and $14, respectively, well within the range considered cost effective. Presumptive treatment regimens to prevent LBW associated with malaria and the subsequent increased risk of mortality during the first year of life are effective and cost effective strategies in areas with both elevated HIV prevalence and malaria transmission rates.

All-cause mortality among young children in western Kenya. VI: the Asembo Bay Cohort Project.

Although all-cause mortality has been used as an indicator of the health status of childhood populations, such data are sparse for most rural areas of sub-Saharan Africa, particularly community-based estimates of infant mortality rates. The longitudinal follow-up of more than 1,500 children enrolled at birth into the Asembo Bay Cohort Project (ABCP) in western Kenya between 1992 and 1996 has provided a fixed birth cohort for estimating all-cause mortality over the first 5 yr of life. We surveyed mothers and guardians of cohort children in early 1999 to determine survival status. A total of 1,260 households were surveyed to determine the survival status of 1,556 live births (99.2% of original cohort, n = 1,570). Most mothers (66%) still resided but 27.5% had migrated, and 5.5% had died. In early 1999, the overall cumulative incidence of all-cause mortality for the entire 1992-1996 birth cohort was 26.5% (95% confidence interval, 24.1-28.9%). Neonatal and infant mortality were 32 and 176 per 1,000 live births, respectively. These community-based estimates of mortality in the ABCP area are substantially higher than for Kenya overall (nationally, infant mortality is 75 per 1,000 live births). The results provide a baseline description of all-cause mortality among children in an area with intense Plasmodium falciparum transmission and will be useful in future efforts to monitor changes in death rates attributable to control programs for specific diseases (e.g., malaria and HIV/AIDS) in Africa.

The burden of malaria in pregnancy in malaria-endemic areas.

Pregnant women in malarious areas may experience a variety of adverse consequences from malaria infection including maternal anemia, placental accumulation of parasites, low birth weight (LBW) from prematurity and intrauterine growth retardation (IUGR), fetal parasite exposure and congenital infection, and infant mortality (IM) linked to preterm-LBW and IUGR-LBW. We reviewed studies between 1985 and 2000 and summarized the malaria population attributable risk (PAR) that accounts for both the prevalence of the risk factors in the population and the magnitude of the associated risk for anemia, LBW, and IM. Consequences from anemia and human immunodeficiency virus infection in these studies were also considered. Population attributable risks were substantial: malaria was associated with anemia (PAR range = 3-15%), LBW (8-14%), preterm-LBW (8-36%), IUGR-LBW (13-70%), and IM (3-8%). Human immunodeficiency virus was associated with anemia (PAR range = 12-14%), LBW (11-38%), and direct transmission in 20-40% of newborns, with direct mortality consequences. Maternal anemia was associated with LBW (PAR range = 7-18%), and fetal anemia was associated with increased IM (PAR not available). We estimate that each year 75,000 to 200,000 infant deaths are associated with malaria infection in pregnancy. The failure to apply known effective antimalarial interventions through antenatal programs continues to contribute substantially to infant deaths globally.

Fcgamma receptor IIa (CD32) polymorphism is associated with protection of infants against high-density Plasmodium falciparum infection. VII. Asembo Bay Cohort Project.

In vitro studies have shown that inhibition of Plasmodium falciparum blood-stage parasite growth by antibody-dependent cellular inhibition is mediated by cooperation between malaria-specific IgG1 and IgG3, but not IgG2, and monocytes via the Fcgamma receptor II (FcgammaRII). A single amino acid substitution at position 131 in FcgammaRIIa is critical in the binding of human IgG subclasses. The hypothesis that the FcgammaRIIa-Arg/Arg131 genotype, which does not bind to IgG2, is a host genetic factor for protection against high-density P. falciparum infection was tested. One hundred eighty-two infants from a large community-based birth cohort study in western Kenya were selected for an unmatched case-control study. Results showed that the infants with the FcgammaRIIa-Arg/Arg131 genotype were significantly less likely to be at risk for high-density falciparum infection, compared with infants with the FcgammaRIIa-His/Arg131 genotype (adjusted odds ratio, 0.278; 95% confidence interval, 0.123-0.627; P=.0021). This finding supports the hypothesis.

Polymorphism in the gene encoding the apical membrane antigen-1 (AMA-1) of Plasmodium falciparum. X. Asembo Bay Cohort Project.

We have investigated the genetic diversity of the gene encoding the apical membrane antigen-1 (AMA-1) in natural populations of Plasmodium falciparum from western Kenya and compared it with parasite populations from other geographic regions. A total of 28 complete sequences from Kenya, Thailand, India, and Venezuela field isolates were obtained. The genetic polymorphism is not evenly distributed across the gene, which is in agreement with the pattern reported in earlier studies. The alleles from Kenya exhibit 20 and 30% more polymorphism than that found in Southeast Asia and Venezuelan alleles, respectively. Based on the gene genealogies derived from sequencing data, no evidence for allele families was found. We have found evidence supporting limited gene flow between the parasite populations, specifically, between the Southeast Asian and Venezuelan isolates; however, no alleles could be linked to a specific geographic region. This study reveals that positive natural selection is an important factor in the maintenance of genetic diversity for AMA-1. We did not find conclusive evidence indicating intragenic recombination is important in the generation of the AMA-1 allelic diversity. The study provides information on the genetic diversity of the AMA-1 gene that would be useful in vaccine development and testing, as well as in assessing factors that are involved in the generation and maintenance of the genetic diversity in P. falciparum.

Glycosylphosphatidylinositol anchors of Plasmodium falciparum: molecular characterization and naturally elicited antibody response that may provide immunity to malaria pathogenesis.

Induction of proinflammatory cytokine responses by glycosylphosphatidylinositols (GPIs) of intraerythrocytic Plasmodium falciparum is believed to contribute to malaria pathogenesis. In this study, we purified the GPIs of P. falciparum to homogeneity and determined their structures by biochemical degradations and mass spectrometry. The parasite GPIs differ from those of the host in that they contain palmitic (major) and myristic (minor) acids at C-2 of inositol, predominantly C18:0 and C18:1 at sn-1 and sn-2, respectively, and do not contain additional phosphoethanolamine substitution in their core glycan structures. The purified parasite GPIs can induce tumor necrosis factor alpha release from macrophages. We also report a new finding that adults who have resistance to clinical malaria contain high levels of persistent anti-GPI antibodies, whereas susceptible children lack or have low levels of short-lived antibody response. Individuals who were not exposed to the malaria parasite completely lack anti-GPI antibodies. Absence of a persistent anti-GPI antibody response correlated with malaria-specific anemia and fever, suggesting that anti-GPI antibodies provide protection against clinical malaria. The antibodies are mainly directed against the acylated phosphoinositol portion of GPIs. These results are likely to be valuable in studies aimed at the evaluation of chemically defined structures for toxicity versus immunogenicity with implications for the development of GPI-based therapies or vaccines.