Biomedical subjects
Publications and source records attributed to Peter G Kremsner.
This study evaluated the efficacy and safety of a 3-day course of artesunate (4 mg/kg/day) for asymptomatic Plasmodium malariae infections. The parasitological cure rates on days 7 and 56 in the group treated with artesunate were 100% and 83%, respectively, compared with no cure in the placebo group (P < 0.0001).
The identification of parasite molecular markers involved in resistance to antimalarial compounds is of great interest for monitoring the development and spread of resistance in the field. Polymorphisms in Plasmodium falciparum multidrug resistance gene 1 (pfmdr1) have been associated with chloroquine resistance and mefloquine susceptibility. In the present study, carried out in Lambaréné, Gabon, we investigated the relationship between the presence of mutations at codons 86, 184, 1034, 1042, and 1246 in the pfmdr1 gene and the success of ultralow-dose mefloquine treatment (1.1 mg/kg of body weight). Sixty-nine patients were included in the study, and depending on the level of in vivo resistance to mefloquine, they were classified as sensitive responders (S), patients with low-grade resistance (RI), and nonresponders (NR). We found that the prevalences of the Tyr-86 mutation among isolates from patients in groups S, RI, and NR were 100, 96, and 90%, respectively, and that the prevalence of the Phe-184 mutation among the isolates was 80% in each group. A prevalence of about 10% point mutations at codons 1042 and 1246 was detected only in isolates from patients in groups RI and NR. There was no statistically significant association between the presence of the Tyr-86 mutation and the in vivo response (P = 0.79). Among the parasite isolates from patients with drug-resistant infections, 83% had the wild-type pfmdr1 genotype (S(1034)-N(1042)-D(1246)). No link between the presence of this genotype and parasite resistance was detected (P = 0.42). Among the isolates analyzed, 85 had double mutations (Y(86)-F(184) or Y(86)-Y(1246)) and 11 had triple mutations (Y(86)-D(1042)-Y(1246), Y(86)-F(184)-Y(1246), or Y(86)-F(184)-D(1042)). These findings are not consistent with those of previous in vitro studies and suggest that further evaluation of pfmdr1 gene polymorphism and in vivo mefloquine sensitivity are needed.
Artesunate (ARS) is a water-soluble artemisinin derivative that is a potential alternative to quinine for the treatment of severe childhood malaria. We studied the pharmacokinetics and bioavailability of ARS given by the intramuscular (i.m.) route in an open crossover study design. Fourteen children were randomized to receive intravenous (i.v.) ARS in a loading dose (2.4 mg/kg of body weight) followed 12 h later by an i.m. dose (1.2 mg/kg) (group I), and 14 children were randomized to receive i.m. ARS (2.4 mg/kg) followed by an i.v. dose of ARS (1.2 mg/kg) (group II). We carried out a two-compartment analysis of ARS and dihydroartemisinin (DHA; the principal antimalarial metabolite) levels in 21 children (groups I and II combined). Absorption of i.m. ARS was rapid, with the maximum concentration of DHA in serum being achieved in less than 1 h in most children (median time to the maximum concentration of drug in serum, 35.1 min; range, 10.8 to 71.9 min). The absolute bioavailability of DHA was a median of 86.4% (range, 11.4 to 462.1%), the median steady-state volume of distribution was 1.3 liters/kg (range, 0.5 to 7.9 liters/kg), and the median clearance was 0.028 liters/kg/min (range, 0.001 to 1.58 liters/kg/min). There were no major adverse events attributable to ARS. Parasite clearance kinetics were comparable between the two treatment groups. These results support the use of i.m. ARS in children with severe malaria.
Explore the source record for details and available documents.
Antibodies from individuals living in areas where malaria is endemic are known to react with parasite-derived erythrocyte surface proteins. The major immunogenic and clonally variant surface antigen described to date is Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1), which is encoded by members of the multicopy var gene family. We report here that rifin proteins (RIF proteins), belonging to the largest known family of variable infected erythrocyte surface-expressed proteins, are also naturally immunogenic. Recombinant RIF proteins were used to analyze the antibody responses of individuals living in an area of intense malaria transmission. Elevated anti-rifin antibody levels were detected in the majority of the adult population tested, whereas the prevalence of such antibodies was much lower in malaria-exposed children. Despite the high degree of diversity between rif sequences and the high gene copy number, it appears that P. falciparum infections can induce antibodies that cross-react with several variant rifin molecules in many parasite isolates in a given community, and the immune response is most likely to be stable over time in a hyperendemic area. The protein was localized by fluorescence microscopy on the membrane of ring and young trophozoite-infected erythrocytes with antibodies from human immune sera with specificities for recombinant RIF protein.
Semi-immunity against Plasmodium falciparum occurs after many infections. In areas of high malaria transmission, the prevalence of asymptomatic parasite carriers increases with age. We investigated P. falciparum genotypes in a cohort of asymptomatic carriers who were followed until they became symptomatic. Blood spots on filter paper and blood smears were collected daily from 10 children in Lambaréné, Gabon. The parasite genotypes present on successive days were determined by a polymerase chain reaction using the polymorphic region of the merozoite surface antigen-2 for typing. The same parasite genotypes persisted in eight out of ten children and parasite densities were low throughout the asymptomatic phase indicating inhibition of parasite growth. Appearance of symptoms was associated with an increase in parasitemia and appearance of novel parasite genotypes. The results suggest that the parasites causing a clinical episode are those against which a child has not yet mounted an efficient protective immune response.
We measured the levels of IgG antibodies with specificity for the variant surface antigens (VSA) of Plasmodium falciparum in plasma samples from a cohort of Gabonese children participating in a longitudinal case-control malaria study. Children with mild malaria had significantly higher anti-VSA IgG responses than their matched counterparts with severe malaria, most markedly during convalescence and when they were healthy. Over the course of the study, almost twice as many children who presented initially with mild rather than severe malaria developed antibodies recognizing the VSA expressed by each of a panel of three isolates, and those with the highest anti-VSA IgG responses had the lowest malaria attack rates. The results suggest that the clinical outcome of P. falciparum infection in young African children depends on their ability to both develop and maintain a broad profile of anti-VSA IgG antibodies, and that this ability is diminished in children who have experienced a severe malaria attack.
We measured cortisol and prolactin concentrations in the peripheral venous blood of 23 non-pregnant and 59 pregnant Gabonese women from the second trimester of pregnancy until delivery. Cortisol concentrations were significantly higher in primigravidae women than in multigravidae women between 20 and 25 weeks' gestational age (166 vs. 132 ng/ml, respectively), between 28 and 37 weeks (226 vs. 161 ng/ml) and at delivery (287 vs. 188 ng/ml). Conversely, plasma prolactin levels were highest in multigravidae women. Cortisol and prolactin concentrations both increased with the period of pregnancy (P = 0.01 and P < 0.01, respectively), suggesting that a sustained increase in cortisol level underlies the increased susceptibility of pregnant women, particularly primigravidae women, to malaria. In support of this hypothesis, we found a significant association between cortisol concentration and Plasmodium falciparum infection, on the one hand, and strong correlations with parasite load in P. falciparum-infected primigravidae women, on the other hand (rho between 0.35 and 0.45 with P < 0.01).
We measured cellular and humoral responses to conserved regions of Plasmodium falciparum merozoite surface proteins 1 and 2 (MSP-1 and MSP-2) at different times during and after acute infection in matched groups of Gabonese children who presented with either mild or severe malaria. We used an MSP-1(19) recombinant protein and peptides corresponding to conserved epitopes in MSP-1 and MSP-2 N- and C-terminal regions. The prevalences of peptide-induced cell-mediated responses were maximal in both groups when they were healthy, but were consistently higher in the mild malaria group, whereas peptide-specific antibody responses were consistently highest in the severe malaria group. Recombinant MSP-1(19) protein-specific antibody levels in the 2 groups were similar both prior to and 1 month post-treatment but declined later when the children were healthy and parasite-free, to a significantly lower level in those admitted with severe malaria, reflecting the profile of the predominant MSP-1(19)-specific immunoglobulin G1 isotype. This finding implies a defect in the ability of children with a history of severe malaria to maintain an antibody response putatively associated with immunity to P. falciparum malaria.
Molecular immunologic determinants of disease severity during Plasmodium falciparum malaria are largely undetermined. Our recent investigations showed that peripheral blood mononuclear cell (PBMC) cyclooxygenase-2 (COX-2) gene expression and plasma prostaglandin E(2) (PGE(2)) production are suppressed in children with falciparum malaria relative to healthy, malaria-exposed children with partial immunity. Furthermore, decreased COX-2/PGE(2) levels were significantly associated with increased plasma interleukin-10 (IL-10), an anti-inflammatory cytokine that inhibits the expression of COX-2 gene products. To determine the mechanism(s) responsible for COX-2-derived PGE(2) suppression, PBMCs were cultured from children with falciparum malaria. PGE(2) production was suppressed under baseline and COX-2-promoting conditions (stimulation with lipopolysaccharide [LPS] and interferon [IFN]-gamma) over prolonged periods, suggesting that an in vivo-derived product(s) was responsible for reduced PGE(2) biosynthesis. Ingestion of hemozoin (malarial pigment) by PBMC was investigated as a source of COX-2/PGE(2) suppression in PBMCs from healthy, malaria-naive adults. In addition, synthetically prepared hemozoin, beta-hematin, was used to investigate the effects of the core iron component of hemozoin, ferriprotoporphyrin-IX (FPIX). Physiologic concentrations of hemozoin or b-hematin suppressed LPS- and IFN-gamma-induced COX-2 mRNA in a time- and dose-dependent manner, resulting in decreased COX-2 protein and PGE(2) production. Suppression of COX-2/PGE(2) by hemozoin was not due to decreased cell viability as evidenced by examination of mitochondrial bioactivity. These data illustrate that ingestion of FPIX by blood mononuclear cells is responsible for suppression of COX-2/PGE(2). Although hemozoin induced overproduction of IL-10, neutralizing IL-10 antibodies failed to restore PGE(2) production. Thus, acquisition of hemozoin by blood mononuclear cells is responsible for suppression of PGE(2) in malaria through inhibition of de novo COX-2 transcripts via molecular mechanisms independent of increased IL-10 production.
Cerebral malaria is a life threatening sequel of Plasmodium falciparum infection and contributes significantly to malaria mortality, especially among children. Accumulation of macrophages and proliferation of microglial cells play key roles in cerebral malaria and are thought to contribute to the pathophysiological alterations observed in these patients, which include enhanced adherence of infected erythrocytes to the cerebral vasculature by expression and secretion of proinflammatory molecules, disruption of the blood-brain barrier, recruitment of other inflammatory cells to the lesion site. In this review, recent advances in the understanding of the involvement of macrophages/microglial cells in the development of cerebral malaria are summarized.
The ability of human NK cells to inhibit the growth in vitro of the asexual blood stages of Plasmodium falciparum was tested. Purified NK cells from donors with no prior exposure to malaria significantly inhibited parasite growth after 48 hours of co-culture in the presence of human immune serum. This inhibition was completely abrogated by pre-treatment of the NK cells with an anti-CD95 (anti-Fas) monoclonal antibody and human Fas-Fc soluble protein. The level of growth inhibition was also substantially reduced by pre-treatment with an anti-CD56 antibody. These two antibodies caused reductions, to varying levels, of the amounts of NK cell-derived granzyme B (GrB) and pro-inflammatory cytokines, but only the anti-CD95 antibody affected the production of soluble Fas ligand (sFasL). Direct destruction of parasite-infected red cells by NK cells, in the absence of serum, was also observed in a standard 51Cr cytotoxicity test, during which N-carboxybenzoxy-L-lysine thiobenzil ester (BLT esterase) activity, which catalyzes serine protease granule release, was detected. The results obtained are indicative of a novel mechanism of NK cell-mediated cytotoxic activity against Plasmodium falciparum-infected red cells, which is mediated in part by both Fas and by GrB.
To investigate if severe malarial anemia is associated with specific cytokine overproduction, we evaluated serum levels of soluble Fas ligand (sFasL), tumor necrosis factor (TNF-alpha) and interleukin-10 (IL-10) from three groups of young children with Plasmodium falciparum infection (asymptomatic cases, uncomplicated malaria cases and severe malarial anemia cases), in a hyperendemic area of Gabon. In uncomplicated cases, only TNF levels were significantly (p < 0.001) increased in comparison to asymptomatic cases with P. falciparum infection. High levels of sFasL, TNF-alpha and IL-10 were associated with low hemoglobin concentrations, sFasL levels were significantly higher in children with severe malarial anemia (p < 0.001) as compared to both other groups. The parasite density was positively correlated with IL-10, TNF-alpha and sFasL levels. TNF-alpha and sFasL, but not IL-10 or parasitemia, were independent predictors of hemoglobin concentrations. These results suggest that, in malaria, a specific dysregulation of the cytokine balance may lead to complications such as severe anemia.
During gestation, inflammatory cytokines are sometimes more abundant than growth-promoting cytokines, and via direct or indirect effects, proinflammatory cytokines lead to intrauterine growth retardation. We used an enzyme-linked immunosorbent assay to measure the concentrations of three proinflammatory cytokines, tumor necrosis factor alpha (TNF-alpha), interleukin-12 (IL-12p40), as well as interleukin-15 (IL-15) and monocyte chemotactic protein-1 (MCP-1), in plasma from peripheral, placental and cord blood of thirty pregnant Gabonese women. All of these women lived in Libreville and Lambaréné, two malaria hyperendemic areas. IL-12p40 concentrations were higher in cord blood than in placental or peripheral blood. The MCP-1 concentration was higher in placental blood, than in peripheral or cord blood. IL-15 concentrations were similar at the three sites. MCP-1 concentrations were higher in the placentas of primiparous women than in those of multiparous women. The highest concentrations were found in infected placentas. IL-15 concentrations were significantly higher in peripheral and placental plasma from uninfected women than in plasma from infected women. Strong positive correlations were found between placental and cord IL-12p40 and IL-15 plasma concentrations. Likewise, a strong positive correlation was found between IL-12p40 and MCP-1 concentrations in cord and peripheral plasma. These results suggest that placental, maternal peripheral and cord blood present different cytokine profiles in response to P. falciparum.
Interleukin-10 (IL-10) is an important multifunctional immunmodulator. There is evidence that IL-10 secretion is associated with certain genetic elements of the proximal IL-10 gene 5'-flanking region. The allelic and genotypic comparison of IL-10 expression by lipopolysaccharide (LPS)- stimulated leukocytes (PBMC) with a recently discovered distal "indel" DNA-sequence variation at - 7400 bp revealed significant inter-individual differences in the IL-10 in vitro production capacity. Homozygotes lacking the three base pairs "GGA" (- 7400del) at this gene locus are characterised by high expression of IL-10 with a median of 1690pg/ml (P <or=0.009). The allelic comparison supports this finding (P <or=0.002). Further analysis of the haplotype -7400/- 1087 showed that homozygotes for - 7400del/- 1087G may be classified as very strong IL-10 responders with a median IL-10 secretion of 2378 pg/ml (P <or=0.025). When leukocytes were stimulated in vitro by dibutyryl-cAMP or infected with Epstein-Barr virus no significant inter-individual differences between the - 7400indel alleles or genotypes and the IL-10 in vitro production capacity were observed. Our findings further the understanding of the complexity of IL-10 gene regulation in relation to defined regulatory gene variations.
The frequency of P. falciparum-specific interleukin (IL)-2-, interferon (IFN)-gamma-, tumor necrosis factor (TNF)-alpha- and IL-10-expressing CD3+ cells was studied in healthy Gabonese children segregated according to their clinical presentation at admission to a longitudinal study of severe and mild malaria. The percentage of IL-2- and TNF-alpha- expressing P. falciparum-specific CD3+ cells was significantly higher in the children with prior mild malaria and less frequent reinfections compared to the children with prior severe malaria and more frequent reinfections. No differences were shown for P. falciparum-specific IFN-gamma and IL-10 expression within CD3+ cells and parasite-non-specific expression of IL-2, IL-4, IL-6, IL-10, IL-13, TNF-alpha, and IFN-gamma within the CD4+, CD8+, TCRgamma\delta+ CD3+ and CD94+ CD3- cell populations, indicating that immunological determinants regulating the susceptibility to malaria in age-matched children are parasite-specific. The ability of P. falciparum-specific T cells to mount a rapid IL-2 and TNF-alpha response might be of significance in preventing severe disease and reinfection.