Biomedical subjects

Peter G Kremsner

Publications and source records attributed to Peter G Kremsner.

At least 55 records · Page 3Linked to original sources

PubMed2005

Differential regulation of beta-chemokines in children with Plasmodium falciparum malaria.

Chemokines regulate the host immune response to a variety of infectious pathogens. Since the role of chemokines in regulating host immunity in children with Plasmodium falciparum malaria has not previously been reported, circulating levels of beta-chemokines (MIP-1alpha, MIP-1beta, and RANTES) and their respective transcriptional profiles in ex vivo peripheral blood mononuclear cells (PBMCs) were investigated. Peripheral blood MIP-1alpha and MIP-1beta levels were significantly elevated in mild and severe malaria, while RANTES levels decreased with increasing disease severity. Beta-chemokine gene expression profiles in blood mononuclear cells closely matched those of circulating beta-chemokines, illustrating that PBMCs are a primary source for the observed pattern of beta-chemokine production during acute malaria. Statistical modeling revealed that none of the chemokines was significantly associated with either parasitemia or anemia. Additional investigations in healthy children with a known history of malaria showed that children with prior severe malaria had significantly lower baseline RANTES production than children with a history of mild malaria, suggesting inherent differences in the ability to produce RANTES in these two groups. Baseline MIP-1alpha and MIP-1beta did not significantly differ between children with prior severe malaria and those with mild malaria. Additional in vitro experiments in PBMCs from healthy, malaria-naïve donors revealed that P. falciparum-derived hemozoin (Hz; malarial pigment) and synthetic Hz (beta-hematin) promote a similar pattern of beta-chemokine gene expression. Taken together, the results presented here demonstrate that children with severe malaria have a distinct profile of beta-chemokines characterized by increased circulating levels of MIP-1alpha and MIP-1beta and decreased RANTES. Altered patterns of circulating beta-chemokines result, at least in part, from Hz-induced changes in beta-chemokine gene expression in blood mononuclear cells.

Chemokine CCL3↗

PubMed2005

Short report: Piloting paperless data entry for clinical research in Africa.

Direct data entry, using handheld computers, may simplify and streamline data management, especially in remote settings. We compared the accuracy of data entry using the current standard practice (a paper-based case report form with double data entry) with that using a personal digital assistant (PDA) in a clinical study in rural Gabon. The rate of discrepant entries was 1.7%. Categorical data (presented in "pull down" menus on the PDA) were more commonly discrepant than were continuous "typed in" data (2.4% versus 1.2%; P = 0.001). Both systems functioned smoothly and no data were lost. The clinicians involved in this study preferred the handheld computers, and their use will be considered in future studies in an African clinical research network.

Africa↗

PubMed2005

Age-dependency of Plasmodium falciparum-specific and non-specific T cell cytokine responses in individuals from a malaria-endemic area.

In areas where Plasmodium falciparum malaria is highly endemic, naturally acquired immunity develops slowly with increasing age. The mechanisms that lead to this protective immunity against P. falciparum are under intense investigation, as they might serve as models for the development of an efficient vaccine. In this study, we aimed to investigate the potential contribution of cell-mediated immune responses to the build-up of anti-malarial immunity by comparing the phenotypes and frequencies of both P. falciparum-specific and non-specific, cytokine-expressing T cells in a cross-sectional study of healthy children and adults, living in a malaria-endemic area in Central Africa. An increased capacity of CD3+ cells to produce interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha, and of the TCRgammadelta+ subset to produce TNF-alpha was seen in adults after stimulation of peripheral blood mononuclear cells (PBMC) with a late-stage, schizont-rich, parasite preparation. Mitogenic stimulation with PMA and ionomycin induced much higher frequencies of IFN-gamma- and TNF-alpha-expressing CD4+, CD8+ as well as TCRgammadelta+ cells in adults, while differences for interleukin (IL)-2 expression were restricted to CD4+ and CD8+ T cells. For IL-10, neither specific nor non-specific stimulations of PBMC were associated with significant age-dependent alterations. Impressive increases in the capacity to produce P. falciparum-specific and non-specific IFN-gamma and TNF-alpha appear to be the main cellular correlates of naturally acquired immunity in Central Africa.

Adolescent↗

PubMed2005

Effectiveness of quinine monotherapy for the treatment of Plasmodium falciparum infection in pregnant women in Lambaréné, Gabon.

Pregnant women participating in a longitudinal immuno-epidemiologic survey in Lambaréné, Gabon, and presenting with Plasmodium falciparum parasitemia at monthly blood smear examinations were offered treatment with oral 7-day quinine monotherapy according to national health guidelines. A total of 50 pregnant women were offered 7-day oral quinine sulfate 10 mg/kg thrice daily. Clinical examinations and laboratory tests were performed on Days 28 and 56 to assess the effectiveness of this standard regimen. By Day 28, the effectiveness of the 7-day quinine regimen was 60% (95% confidence interval: 46-72%). We conclude that a 7-day course of quinine has a poor effectiveness and that alternative treatment regimens for malaria in pregnant women should be assessed.

Adult↗

PubMed2005

Assessment of a simplified method for counting leukocytic malaria pigment.

Severe and fatal malaria is associated with the increased presence of malaria hemozoin in peripheral phagocytes. Large studies of this relationship are hampered by the fact that identifying and counting phagocytes on thick blood smears is time consuming. Distinguishing which mononuclear cells are monocytes and which granulocytes are neutrophils requires time and careful training. In this study, we evaluated a simplified method in which only the proportions of hemozoin-containing mononuclear cells and granulocytes are counted. Thick blood films from 471 Gabonese children with malaria were evaluated. We found a linear relationship and a strong correlation between the proportions of hemozoin-containing monocytes versus mononuclear cells (r = 0.85) and neutrophils versus polymorphonuclear cells (r = 0.93), respectively. The two methods had similar predictive values, as estimated by receiver operating characteristics curves. This simplified method can be used to estimate the amount of extra-erythrocytic pigment in peripheral blood, and we suggest that it may be particularly suitable for very large studies.

Animals↗

PubMed2005

5-day nonobserved artesunate monotherapy for treating uncomplicated Falciparum malaria in young Gabonese children.

Despite different recommendations from WHO and national authorities, artesunate monotherapy is increasingly used for treating African children with malaria. A 5-day course of oral artesunate (first day: 4 mg/kg body weight, observed intake; and 2 mg/kg body weight on the following days with nonobserved drug intake) yielded a PCR-corrected Day 28 cure rate of 90% (45 of 50 patients; CI 78-97%) in Gabonese children aged between 2 and 18 months. Artesunate was well tolerated, and no severe adverse events were reported.

Animals↗

PubMed2004

Circulating levels of the interleukin (IL)-4 receptor and of IL-18 in patients with Plasmodium falciparum malaria.

Circulating levels of sIL-4R, IL-18 and IFN-gamma were studied by ELISA in 36 Gabonese patients with Plasmodium falciparum malaria (29 children, 7 adults). Drug induced clearance of parasitemia, studied in 22 patients with mild disease, was accompanied by a rapid decrease of sIL-4R and IFN-gamma to normal values and an increase of circulating IL-18, suggesting the downregulation of a type 2 biased immune response and a dissociated type 1 responsiveness while resolving parasitemia. Comparing subgroups with hyperparasitemia/severe anemia and mild malaria, children with severe malaria had significant higher levels of sIL-4R and IFN-gamma, whereas IL-18 levels were not statistically different. Furthermore, among those children, higher levels of circulating IL-18 correlated with a lower degree of parasitemia.

Adolescent↗

PubMed2004

Assessment of volume depletion in children with malaria.

BACKGROUND: The degree of volume depletion in severe malaria is currently unknown, although knowledge of fluid compartment volumes can guide therapy. To assist management of severely ill children, and to test the hypothesis that volume changes in fluid compartments reflect disease severity, we measured body compartment volumes in Gabonese children with malaria. METHODS AND FINDINGS: Total body water volume (TBW) and extracellular water volume (ECW) were estimated in children with severe or moderate malaria and in convalescence by tracer dilution with heavy water and bromide, respectively. Intracellular water volume (ICW) was derived from these parameters. Bioelectrical impedance analysis estimates of TBW and ECW were calibrated against dilution methods, and bioelectrical impedance analysis measurements were taken daily until discharge. Sixteen children had severe and 19 moderate malaria. Severe childhood malaria was associated with depletion of TBW (mean [SD] of 37 [33] ml/kg, or 6.7% [6.0%]) relative to measurement at discharge. This is defined as mild dehydration in other conditions. ECW measurements were normal on admission in children with severe malaria and did not rise in the first few days of admission. Volumes in different compartments (TBW, ECW, and ICW) were not related to hyperlactataemia or other clinical and laboratory markers of disease severity. Moderate malaria was not associated with a depletion of TBW. CONCLUSIONS: Significant hypovolaemia does not exacerbate complications of severe or moderate malaria. As rapid rehydration of children with malaria may have risks, we suggest that fluid replacement regimens should aim to correct fluid losses over 12-24 h.

Child↗

PubMed2004

Rare, highly pyrimethamine-resistant alleles of the Plasmodium falciparum dihydrofolate reductase gene from 5 African sites.

In eastern and southern Africa, there has been a rapid increase in the prevalence of alleles with mutations in the Plasmodium falciparum dihydrofolate reductase gene (dhfr) associated with increased risk of clinical failure of sulfadoxine-pyrimethamine (S/P). Molecular methods for surveillance of these mutations are now widespread, but the usual analysis detects only the most prevalent allele in a polyclonal sample. We used a yeast-expression system to identify rare, highly pyrimethamine-resistant alleles of dhfr in isolates from 5 African countries--Kenya, Tanzania, Malawi, Gabon, and Nigeria. Only the isolates from Nigeria yielded significant numbers of novel resistant alleles, and only 1 of the alleles from any location showed a >3-fold increase in resistance to S/P or to chlorproguanil-dapsone. Overall, these results suggest that dhfr alleles that confer high levels of resistance to antifolates are rare, even in eastern and southern Africa, where pyrimethamine has been intensively used.

Alleles↗

PubMed2004

Fosmidomycin-clindamycin for the treatment of Plasmodium falciparum malaria.

It has been demonstrated that fosmidomycin has good tolerability and rapid onset of action, but late recrudescences preclude its use alone; in vitro, clindamycin has been shown to act synergistically with fosmidomycin against Plasmodium falciparum. We conducted a study in pediatric outpatients with P. falciparum malaria in Gabon to evaluate the efficacy and safety of an oral combination of fosmidomycin-clindamycin of 30 mg/kg and 10 mg/kg of body weight, respectively, every 12 h. Patients 7-14 years old were recruited in cohorts of 10. The first 10 patients were treated for 5 days. The duration of treatment was then incrementally shortened in intervals of 1 day if >85% of the patients in a cohort were cured by day 14. All dosing regimens were well tolerated, and no serious adverse events occurred. Asexual parasites and fever rapidly cleared in all patients. Cure ratios of 100% on day 14 were achieved with treatment durations of 5 (10/10 patients), 4 (10/10 patients), 3 (10/10 patients), and 2 days (10/10 patients); 1 day of treatment led to a cure ratio of 50% (5/10 patients). Fosmidomycin-clindamycin is safe and well tolerated, and short-course regimens achieved high efficacy in children with P. falciparum malaria. Fosmidomycin-clindamycin is a promising novel treatment option for malaria.

Administration, Oral↗

PubMed2004

Shared breastfeeding in central Africa.

In this study, shared breastfeeding is described asa novel risk factor for vertical HIV transmission. This cross-sectional survey conducted in the central African country Gabon found that 40% of lactating mothers also breastfed other children than their own, and as many children were additionally breastfed by other women. Shared breastfeeding is increasing the exposure to potentially infectious individuals and has therefore to be considered in breastfeeding recommendations.

Breast Feeding↗

PubMed2004

Plasmodium induces swelling-activated ClC-2 anion channels in the host erythrocyte.

Intraerythrocytic growth of the human malaria parasite Plasmodium falciparum depends on delivery of nutrients. Moreover, infection challenges cell volume constancy of the host erythrocyte requiring enhanced activity of cell volume regulatory mechanisms. Patch clamp recording demonstrated inwardly and outwardly rectifying anion channels in infected but not in control erythrocytes. The molecular identity of those channels remained elusive. We show here for one channel type that voltage dependence, cell volume sensitivity, and activation by oxidation are identical to ClC-2. Moreover, Western blots and FACS analysis showed protein and functional ClC-2 expression in human erythrocytes and erythrocytes from wild type (Clcn2(+/+)) but not from Clcn2(-/-) mice. Finally, patch clamp recording revealed activation of volume-sensitive inwardly rectifying channels in Plasmodium berghei-infected Clcn2(+/+) but not Clcn2(-/-) erythrocytes. Erythrocytes from infected mice of both genotypes differed in cell volume and inhibition of ClC-2 by ZnCl(2) (1 mm) induced an increase of cell volume only in parasitized Clcn2(+/+) erythrocytes. Lack of ClC-2 did not inhibit P. berghei development in vivo nor substantially affect the mortality of infected mice. In conclusion, activation of host ClC-2 channels participates in the altered permeability of Plasmodium-infected erythrocytes but is not required for intraerythrocytic parasite survival.

Animals↗

PubMed2004

Analysis of IgG with specificity for variant surface antigens expressed by placental Plasmodium falciparum isolates.

BACKGROUND: Pregnancy-associated malaria (PAM) is caused by Plasmodium falciparum-infected erythrocytes that can sequester in placental intervillous space by expressing particular variant surface antigens (VSA) that can mediate adhesion to chondroitin sulfate A (CSA) in vitro. IgG antibodies with specificity for the VSA expressed by these parasites (VSAPAM) are associated with protection from maternal anaemia, prematurity and low birth weight, which is the greatest risk factor for death in the first month of life. METHODS: In this study, the development of anti-VSAPAM antibodies in a group of 151 women who presented to the maternity ward of Albert Schweitzer Hospital in Lambaréné, Gabon for delivery was analysed using flow cytometry assays. Plasma samples from placenta infected primiparous women were also investigated for their capacity to inhibit parasite binding to CSA in vitro. RESULTS: In the study cohort, primiparous as well as secundiparous women had the greatest risk of infection at delivery as well as during pregnancy. Primiparous women with infected placentas at delivery showed higher levels of VSAPAM-specific IgG compared to women who had no malaria infections at delivery. Placental isolates of Gabonese and Senegalese origin tested on plasma samples from Gabon showed parity dependency and gender specificity patterns. There was a significant correlation of plasma reactivity as measured by flow cytometry between different placental isolates. In the plasma of infected primiparous women, VSAPAM-specific IgG measured by flow cytometry could be correlated with anti-adhesion antibodies measured by the inhibition of CSA binding. CONCLUSION: Recognition of placental parasites shows a parity- and sex- dependent pattern, like that previously observed in laboratory strains selected to bind to CSA. Placental infections at delivery in primiparous women appear to be sufficient to induce functional antibodies which can both recognize the surface of the infected erythrocytes as well as block their binding to CSA. The correlation between serum reactivities of placental field isolates from different geographic locations and collected at different times is indicative of the conserved nature of the antigen(s) mediating PAM.

Animals↗

PubMed2004

No change in parasite genotype during single episodes of Plasmodium falciparum malaria in Gabonese children.

Patients living in endemic areas can carry a mixture of Plasmodium falciparum genotypes. To investigate the genetic composition of parasite genotypes in malaria patients during the acute phase of the infection, we performed close follow-ups of 17 Gabonese pediatric patients aged 2-7 years. Capillary blood samples were taken on admission and every 4-6 h after the start of quinine therapy. Merozoite surface protein 2 (MSP2) genotypes were used to assess the parasites' genetic characteristics in each sample. We found that each patient carried parasites with the same genotypic pattern throughout the infection.

Animals↗

PubMed2004

Impact of increasing consultation fees on malaria in Africa.

To evaluate the impact of the increase in consultation fees on malaria incidence in children presenting in the outpatient clinic of a privately funded hospital, we measured the impact of two fee increases on the number of pediatric outpatients. A 74% reduction in outpatients and a 78% reduction in malaria cases occurred in a course of four years. No differences were observed in an adjacent public hospital that does not charge consultation fees. This surprisingly strong effect may be the basis for increase in malaria morbidity and mortality, since in the time course of 4 years, an estimated 3000 children did not receive adequate malaria treatment in this region. Furthermore, it may drive parasite resistance, due to inadequate auto-medication.

Child↗

PubMed2004

DNA phasing by TA dinucleotide microsatellite length determines in vitro and in vivo expression of the gp91phox subunit of NADPH oxidase and mediates protection against severe malaria.

Reactive oxygen intermediates (ROIs) play a major role in the nonspecific innate immune response to invading microorganisms, such as Plasmodium falciparum. In a search for genetic markers that determine differences in production of ROI, we detected a highly polymorphic region of dinucleotide TA repeats approximately 550 bp upstream of the NADPH oxidase gp91(phox) subunit promoter. We genotyped 183 matched Gabonese children with severe or mild malaria. Repeat lengths TA(11) and TA(16) differed significantly in frequency between mild and severe infection, which suggests protection against severe malaria. Both repeat lengths showed lower levels of NADPH oxidase and promoter activities, which can be explained by a cyclic trend in TA repeat length with a period of approximately 5, which indicates the necessity of correct DNA phasing between 2 possible control regions in the promoter. We provide a molecular model of how DNA phasing generated by TA dinucleotide polymorphisms may influence the expression level and protect against severe malaria.

Animals↗

PubMed2004

Responses to Toll-like receptor ligands in children living in areas where schistosome infections are endemic.

To study the effect of repeated challenge of the innate immune system with pathogen-associated molecular patterns, cytokine responses to schistosomal lipids and bacterial lipopolysaccharide (LPS) were analyzed in schoolchildren living in an area in Gabon where schistosomiasis, a helminth infection that is chronic in nature, is endemic. A schistosomal phosphatidylserine (PS) fraction containing the Toll-like receptor (TLR)-2 ligand lyso-PS stimulated the production of interleukin (IL)-8, IL-10, IL-6, and tumor necrosis factor (TNF)-alpha in children without Schistosoma haematobium infection. However, in infected children, the responses to this stimulus were lower, in particular for production of IL-8 and TNF-alpha. Responses to the TLR4 ligand, LPS, followed a similar pattern. In contrast, schistosomal adult worm glycolipids that did not stimulate any of the TLRs tested induced IL-8 and IL-6 responses that were significantly higher in schistosome-infected children than in schistosome-uninfected children. These results indicate that relentless exposure to pathogens can lead to altered responses to TLR ligands.

Adolescent↗

PubMed2004

Long-term treatment of intestinal helminths increases mite skin-test reactivity in Gabonese schoolchildren.

BACKGROUND: Several studies have shown an inverse association between helminth infections and atopy, but none have clearly established that the pathogens themselves, rather than other associated factors, cause the suppression of atopy. To show a direct link, prospective intervention studies are required. METHODS: A randomized, controlled trial was performed to study whether repeated anthelminthic treatment results in increased allergic sensitivity to house dust mites (HDMs) in chronically infected children. The trial population consisted of 317 Gabonese schoolchildren with a high prevalence of intestinal helminths. Intervention consisted of treatment every 3 months with praziquantel and mebendazole and with placebo in the control group. Follow-up lasted 30 months: at 6-month intervals, skin-test sensitivity to mites, helminth infection status, and levels of total IgE were determined. RESULTS: Treatment resulted in a significant increase in the rate of developing skin sensitivity to HDMs (hazard ratio, 2.51; 95% confidence interval, 1.85-3.41), which was mediated, in part, by reductions in Ascaris and/or Trichuris infections. Levels of total IgE were reduced, but this did not mediate the effect of treatment on skin-test reactivity. CONCLUSIONS: Anthelminthic treatment of chronically infected children results in increased atopic reactivity, which indicates that helminths directly suppress allergic reactions.

Adolescent↗