Biomedical subjects

Peter G Kremsner

Publications and source records attributed to Peter G Kremsner.

At least 37 records · Page 2Linked to original sources

PubMed2006

In vitro activity of ferroquine (SAR97193) is independent of chloroquine resistance in Plasmodium falciparum.

Nowadays, chloroquine-resistant malaria appears in almost all endemic regions. Ferroquine is a derivative of chloroquine and shows good activity in vitro and in animal models, but the development of cross-resistance is of concern. We tested in vitro susceptibilities of Plasmodium falciparum field isolates from Gabon to ferroquine, chloroquine, and artesunate. As expected, chloroquine resistance was present in all parasite isolates (median 50% inhibitory concentration = 113 nmol/L). Ferroquine (1.94 nmol/L) and artesunate (0.96 nmol/L) were highly active, and no significant correlation between any of the three drugs was observed. In contrast to our findings, previous studies showed an association between chloroquine and ferroquine activities. We could reproduce this association by using different initial parasitemias, but analysis of covariance revealed that initial parasitemia and not parasite strain was the critical determinant for the correlation between chloroquine and ferroquine activities. We conclude that ferroquine is highly active in chloroquine-resistant parasites, and we anticipate no enhanced selection for resistance against ferroquine in chloroquine-resistant parasites.

Aminoquinolines↗

PubMed2006

Increase in annexin V-positive B cells expressing LILRB1/ILT2/CD85j in malaria.

The outcome of a Plasmodium falciparum infection differs greatly between patients, ranging from an asymptomatic carrier status to the most severe characteristics influenced by activating and inhibiting immune factors. The inhibitory leukocyte immunoglobulin-like receptor (LILRB1/CD85j) plays an important role in the immune response as regulator of cytotoxic T cells and of premature activation and clonal expansion of B cells. To investigate its role in malaria, we analyzed blood samples from malaria patients by cytometric analysis. We found a similar expression pattern of CD85j on PBMC in both patients and healthy children. However, malaria patients presented significantly more CD85j+ CD19+ B cells, which also bound annexin V an indicator of early cell death. We compared the plasma levels of several cytokines, since it was speculated that CD85j expression influences cytokine release. Production of inflammatory cytokines was significantly increased in severe malaria cases. We suggest that in malaria, dying B cells contribute to the overwhelming cytokine release and the impairment of the immune memory.

Annexin A5↗

PubMed2005

Reduced cord blood immune effector-cell responsiveness mediated by CD4+ cells induced in utero as a consequence of placental Plasmodium falciparum infection.

To determine mechanisms of neonatal parasite antigen (Ag)-specific immune suppression associated with placental Plasmodium falciparum infection, we isolated cord blood mononuclear cells (CBMCs) from Gabonese neonates born to mothers with differing histories of P. falciparum infection and performed ex vivo and in vitro studies to evaluate immune regulatory activity. We found increased ex vivo percentages of CD4(+)CD25(hi) and CD4(+)CD25(+)CTLA-4(+) cells and increased interleukin (IL)-10 responses to parasite Ag in vitro in CBMCs from neonates born to mothers with placental P. falciparum infection at delivery. Depleting CBMCs of CD4(+)CD25(+) cells before cell culture led to the abrogation of parasite Ag-specific IL-10 responses, to enhanced interferon- gamma responses, and to enhanced expression of CD25 on CD8(+) T cells and of major histocompatibility complex class I and II on monocytes. These data demonstrate that parasite Ag-specific CD4(+) regulatory cells are generated in utero as a consequence of placental P. falciparum infection.

Adult↗

PubMed2005

Persistent Epstein-Barr viral reactivation in young African children with a history of severe Plasmodium falciparum malaria.

Epstein-Barr virus (EBV) and Plasmodium falciparum have overlapping distributions and are thought to have causal interactions, particularly with regard to the aetiology of endemic Burkitt's lymphoma. Using real-time PCR, we quantified and compared EBV DNA levels in the blood before and after antimalarial treatment of age- and gender-matched groups of Gabonese children who presented with either mild or severe P. falciparum malaria. Following treatment, the prevalence of EBV DNA declined in the mild malaria group but increased in the severe malaria group, and a significantly higher proportion of the latter had EBV DNA detectable in their blood when they were healthy and parasite free (67% vs. 39%; P=0.013). High EBV DNA loads were associated with more malaria attacks and with elevated plasma concentrations of both TNF-alpha and IL-12p40. Significantly more under 5 year olds had EBV DNA, highlighting the strong age dependence of the interaction between the two pathogens. These findings confirm that EBV is reactivated during acute P. falciparum malaria but, importantly, also reveal that: (i) EBV activity persists at a higher frequency in children with a history of severe malaria; and (ii) higher peripheral blood EBV DNA loads are associated with susceptibility to more frequent P. falciparum episodes and with altered cytokine activity.

Antimalarials↗

PubMed2005

Influence of carriage of hemoglobin AS and the Fc gamma receptor IIa-R131 allele on levels of immunoglobulin G2 antibodies to Plasmodium falciparum merozoite antigens in Gabonese children.

BACKGROUND: To extend our previous findings showing an imbalanced distribution of immunoglobulin G2 (IgG2) antibodies to Plasmodium falciparum merozoite surface protein 2 (MSP2) and a higher frequency of infection with multiple P. falciparum strains in Gabonese children with sickle cell trait (hemoglobin AS), human Fc gamma receptor (Fc gamma R) IIa (CD32) polymorphism and the rate of in vitro invasion of red blood cells (RBCs) from subjects with either hemoglobin AA or AS by multiple P. falciparum strains were investigated. METHODS: Fc gamma RIIa mutation at amino acid position 131 (arginine or histidine) was detected by polymerase chain reaction, and in vitro cultures for parasites were used to assess the invasion rate. RESULTS: Fc gamma RIIa polymorphism is normally distributed in this population, with no preferential carriage by children with hemoglobin AS. Lower levels of IgG2 subclass antibodies to MSP2 peptides were independently associated with the Fc gamma RIIa-R131 allele and with carriage of hemoglobin AS. Our data suggest that IgG3 antibody responses to MSP2 epitopes could be exacerbated by lower IgG2 levels in children with hemoglobin AS. CONCLUSIONS: The higher rate of invasion of RBCs in the presence of multiple strains may indicate that several invasion pathways are solicited simultaneously, and the longer persistence of ring forms in RBCs from the subjects with hemoglobin AS might reflect a slower multiplication phase, leading to a longer circulation and enhanced phagocytosis of these nonpathogenic parasite forms. This may contribute to the protection against P. falciparum malaria observed in children with hemoglobin AS.

Alleles↗

PubMed2005

Amplification of Plasmodium falciparum multidrug resistance gene 1 in isolates from Gabon.

The study of molecular markers of drug resistance is particularly important in surveillance studies of drugs, such as mefloquine, that still retain efficacy in sub-Saharan Africa yet have encountered resistance elsewhere. In a recent study in Thailand, we identified amplification of the Plasmodium falciparum multidrug resistance gene 1 (pfmdr1) as being the most important predictor of in vitro drug resistance and in vivo failure of mefloquine monotherapy. Here we report amplification of pfmdr1 in >5% of patient samples from Lambarene, Gabon, collected in 1995. None of the samples collected 7 years later showed pfmdr1 amplification, suggesting that parasites with increased numbers of pfmdr1 copies have not substantially spread through the population. Nevertheless, the detection of multicopy pfmdr1 in African parasites suggests a high potential for rapid selection for resistance, implying that mefloquine use in Africa should be considered only as part of combination therapy.

ATP-Binding Cassette Transporters↗

PubMed2005

Artesunate-clindamycin versus quinine-clindamycin in the treatment of Plasmodium falciparum malaria: a randomized controlled trial.

BACKGROUND: Artemisinin-based drug combinations are the mainstay in the fight against drug-resistant malaria in Africa. Currently available antimalarial drug combinations that include artemisinins are pharmacokinetically unmatched and are therefore potentially increasing the risk of selection of resistant mutants in areas in which the rate of transmission of malaria is high. We tested the potential value of artemisinin-based combination therapy with a short elimination half-life for the treatment of uncomplicated Plasmodium falciparum malaria in sub-Saharan Africa. METHODS: We conducted an open-label, randomized, controlled clinical trial to evaluate the efficacy and tolerability of oral artesunate-clindamycin therapy given twice daily for 3 days (artesunate, 2 mg/kg, and clindamycin, 7 mg/kg, per dose), compared with a standard quinine-clindamycin regimen given twice daily for 3 days (quinine, 15 mg/kg, and clindamycin, 7 mg/kg, per dose), for the treatment of uncomplicated falciparum malaria in 100 Gabonese children aged 3-12 years. The primary end point of the study was the polymerase chain reaction-corrected cure rate for the per-protocol population. RESULTS: The activity of artesunate-clindamycin was comparable to that of quinine-clindamycin in the per-protocol analysis of cure rates at day 28 of follow-up (87% versus 94%). No serious adverse events were reported, and tolerability was good and was similar in both groups. Times to clearance of fever and clearance of parasites were significantly shorter in the artesunate-clindamycin group. CONCLUSIONS: Artesunate-clindamycin and other matching artemisinin-based combinations with a short plasma half-life merit further attention for use in regions in which the rate of transmission of malaria is high.

Antimalarials↗

PubMed2005

Increased specific T cell cytokine responses in patients with active pulmonary tuberculosis from Central Africa.

An understanding of T cell responses that are crucial for control of Mycobacterium tuberculosis (MTB) has major implications for the development of immune-based interventions. We studied the frequency of purified protein derivative (PPD)-specific CD3) cells expressing interleukin-2 (IL)-2, gamma interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and IL-10 in HIV-negative pulmonary tuberculosis patients (TB, n=30) as well as in healthy individuals (controls, n=21) from Central Africa. Increased frequencies of PPD-stimulated CD3+ cells expressing IL-2, IFN-gamma, and TNF-alpha in TB were seen when compared with frequencies of controls. The presence of type 1 cytokine biased responses in TB patients was supported by a shift in the distribution pattern of cytokine expression from exclusively IL-2 or TNF-alpha expression seen in controls towards an increased frequency of IFN-gamma/IL-2 or IFN-gamma/TNF-alpha co-expression in TB. Higher levels of PPD-induced IFN-gamma in the supernatants from TB patients than from controls were found, which correlated with its intracellular expression. PPD was a weak inducer of IL-10 in T cells and insufficient in promoting cytokine production in TCRgammadelta+CD3+ cells. Non-specific stimulation with PMA and ionomycin revealed increased frequencies of CD4+ cells expressing IFN-gamma in controls, while expression of IL-2, IL-4, IL-10, IL-13, and TNF-alpha was not different. Non-specific cytokine responses of TCRgammadelta+CD3+ cells were similar in all groups. Pulmonary TB in Central Africa is associated with enhanced expression and secretion of specifically induced cytokines that are frequently implicated in host defense against MTB.

Adolescent↗

PubMed2005

The sickle cell trait is associated with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens.

The sickle cell trait (HbAS) protects against severe Plasmodium falciparum malaria in young African children. We investigated the extent of the association between HbAS and antibodies directed to parasite-derived variant surface antigens (VSAs) on the membrane of infected erythrocytes. We measured immunoglobulin G (IgG) responses with specificity for VSAs of 2 heterologous parasite isolates in 458 Gabonese children aged between 6 months and 11 years. Logistic regression analyses showed a highly significant independent association (P<.001) between carriage of HbAS and the presence of IgG anti-VSA responses; this association was related specifically to IgG1 and IgG4 subclasses in the anti-VSA profile. IgG2 and IgG3 anti-VSA responses were both independently associated with older age, consistent with the pattern observed in semi-immune adults. The results imply that enhanced levels of cross-reactive anti-VSA responses in children with HbAS may be intimately associated with the protection they have against malaria.

Animals↗

PubMed2005

Activation status of cord blood gamma delta T cells reflects in utero exposure to Plasmodium falciparum antigen.

BACKGROUND: Placental Plasmodium falciparum infection modulates neonatal cell-mediated immune responses and is associated with increased susceptibility of infants to malaria. METHODS: By flow-cytometric analysis of maternal peripheral and cord blood samples collected at delivery, we measured and compared the activation status and proinflammatory cytokine activity of T cells from women segregated into groups according to malaria status. RESULTS: Stimulation with phorbol myristate acetate/ionomycin resulted in the highest percentages of tumor necrosis factor-alpha- and interferon-gamma-positive gamma delta T cells in peripheral blood samples and in corresponding cord blood samples from those treated for malaria during pregnancy. Cord blood samples from this group also contained significantly higher percentages of CD69(+) and CD25(+) gamma delta T cells and CD3(+) T cells, compared with samples from either the group with active placental P. falciparum infection at delivery or the group with no infection. Proinflammatory cytokine activity of cells from the group with placental P. falciparum infection at delivery was either similar to or lower than that of cells from the group with no infection. CONCLUSIONS: The findings imply that treatment of P. falciparum malaria during pregnancy leads to enhanced innate immune T cell activation and proinflammatory cytokine responses in both maternal and fetal compartments. Ongoing placental P. falciparum infection, conversely, is associated with an absence of such activity.

Adolescent↗

PubMed2005

Clinical and parasitological characteristics of puerperal malaria.

BACKGROUND: Women with semi-immunity to malaria who live in regions where the disease is endemic are at increased risk for more frequent and severe episodes of malaria during pregnancy. Recent findings indicate that this increased risk might persist beyond delivery, but the underlying mechanisms for this change in risk are poorly understood. METHODS: One hundred fifty women were included in a cohort study in Lambaréné, Gabon, and were actively followed up weekly for 10 weeks after delivery, as were nonpregnant control women who had been matched to them by location and age. Parasites in samples of placenta and blood were genotyped by use of polymerase chain reaction amplification of the merozoite surface antigen 2 gene and the subtelomeric variable open reading frame gene of Plasmodium falciparum. RESULTS: Eleven puerperal women had cases of clinical malaria, compared with 1 control woman (rate ratio, 9.8; P=.006). Eighteen puerperal women had P. falciparum parasitemia, compared with 6 control women (rate ratio, 2.7; P=.03). Five of 16 puerperal women (31%) with parasitemia on follow-up had identical parasites in their placentas and blood, and 11 of these cases (69%) were the result of reinfection. Puerperal women remained at equal risk for the development of parasitemia throughout the first 10 weeks after delivery. Use of bed nets, use of chloroquine prophylaxis during pregnancy, presence of malaria episodes during pregnancy, gravidity, and age were not associated with the acquisition of parasitemia during follow-up. CONCLUSIONS: Compared with nonpregnant women, puerperal women have a considerably increased risk for the development of malaria and/or parasitemia. This increased risk is caused both by the recurrence of P. falciparum parasitemia and by the increased susceptibility to new infections, although the latter plays a more significant role.

Adult↗

PubMed2005

IFN-gamma and IL-10 mediate parasite-specific immune responses of cord blood cells induced by pregnancy-associated Plasmodium falciparum malaria.

Available evidence suggests that immune cells from neonates born to mothers with placental Plasmodium falciparum (Pf) infection are sensitized to parasite Ag in utero but have reduced ability to generate protective Th1 responses. In this study, we detected Pf Ag-specific IFN-gamma(+) T cells in cord blood from human neonates whose mothers had received treatment for malaria or who had active placental Pf infection at delivery, with responses being significantly reduced in the latter group. Active placental malaria at delivery was also associated with reduced expression of monocyte MHC class I and II in vivo and following short term in vitro coculture with Pf Ag compared with levels seen in neonates whose mothers had received treatment during pregnancy. Given that APC activation and Th1 responses are driven in part by IFN-gamma and down-regulated by IL-10, we examined the role of these cytokines in modulating the Pf Ag-specific immune responses in cord blood samples. Exogenous recombinant human IFN-gamma and neutralizing anti-human IL-10 enhanced T cell IFN-gamma production, whereas recombinant human IFN-gamma also restored MHC class I and II expression on monocytes from cord blood mononuclear cells cocultured with Pf Ag. Accordingly, active placental malaria at delivery was associated with increased frequencies of Pf Ag-specific IL-10(+)CD4(+) T cells in cord blood mononuclear cell cultures from these neonates. Generation and maintenance of IL-10(+) T cells in utero may thus contribute to suppression of APC function and Pf Ag-induced Th1 responses in newborns born to mothers with placental malaria at delivery, which may increase susceptibility to infection later in life.

Animals↗

PubMed2005

Severe falciparum malaria in Gabonese children: clinical and laboratory features.

BACKGROUND: Malaria continues to claim one to two million lives a year, mainly those of children in sub-Saharan Africa. Reduction in mortality depends, in part, on improving the quality of hospital care, the training of healthcare workers and improvements in public health. This study examined the prognostic indicators of severe falciparum malaria in Gabonese children. METHODS: An observational study examining the clinical presentations and laboratory features of severe malaria was conducted at the Centre Hospitalier de Libreville, Gabon over two years. Febrile children aged from 0 to 10 years with Plasmodium falciparum infection and one or more features of severe malaria were enrolled. RESULTS: Most children presenting with severe falciparum malaria were less than 5 years (92.3% of 583 cases). Anaemia was the most frequent feature of severe malaria (67.8% of cases), followed by respiratory distress (31%), cerebral malaria (24%) hyperlactataemia (16%) and then hypoglycaemia (10%). Anaemia was more common in children under 18 months old, while cerebral malaria usually occurred in those over 18 months. The overall case fatality rate was 9%. The prognostic indicators with the highest case fatality rates were coma/seizures, hyperlactataemia and hypoglycaemia, and the highest case fatality rate was in children with all three of these features. CONCLUSIONS: Prompt and appropriate, classification and treatment of malaria helps identify the most severely ill children and aids early and appropriate management of the severely ill child.

Age Distribution↗

PubMed2005

Malaria and asymptomatic parasitaemia in Gabonese infants under the age of 3 months.

We determined the incidence of both malaria and asymptomatic parasitaemia in infants under the age of 3 months within the framework of a longitudinal cohort study in Lambaréné, Gabon, between December 2002 and July 2004. Of 878 infants who were included at birth, we identified malaria in three infants and, additionally, asymptomatic parasitaemia in six infants. The malaria incidence density was 1.1/1000 person-months or 0.1% of observations. Our findings underpin the notion that the incidence of malaria and parasitaemia in infants below the age of 3 months is very low.

Adult↗

PubMed2005

Short-course regimens of artesunate-fosmidomycin in treatment of uncomplicated Plasmodium falciparum malaria.

Fosmidomycin is effective against malaria, but it needs to be given for > or =4 days when used alone. We conducted a study of 50 children with Plasmodium falciparum malaria to evaluate the safety and efficacy of consecutively shortened regimens of artesunate-fosmidomycin (1 to 2 mg/kg of body weight and 30 mg/kg of body weight, respectively; doses given every 12 hours). All dosing regimens were well tolerated. Artesunate-fosmidomycin acted rapidly, resulting in consolidated geometric mean parasite and fever clearance times of 24 h and 15 h, respectively. Treatment regimens of > or =2 days led to cure ratios of 100% by day 14 (39/39; 95% confidence interval [95% CI], 91% to 100%). Most importantly, the 3-day regimen achieved 100% cure on day 28 (10/10; 95% CI, 69% to 100%). Treatment with artesunate-fosmidomycin was associated with transient grade I or II neutropenia (absolute neutrophil counts of 750 to 1,200/microl and 400 to 749/microl, respectively) in six or two patients, respectively. Artesunate-fosmidomycin demonstrates the feasibility and potential value of short-course artemisinin-based combination chemotherapy with rapidly eliminated combination partners.

Antimalarials↗

PubMed2005

Neonatal and maternal immunological responses to conserved epitopes within the DBL-gamma3 chondroitin sulfate A-binding domain of Plasmodium falciparum erythrocyte membrane protein 1.

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) mediates the adherence of P. falciparum-infected erythrocytes to placental syncytiotrophoblasts via interactions with chondroitin sulfate A (CSA), a characteristic of pregnancy-associated malaria. Pregnancy-associated malaria predicts increased susceptibility of newborns to malaria, and it is postulated that transplacental passage of parasite antigen induces immune regulatory activity in the neonate. We wished to examine the immune responsiveness to a CSA-binding domain of PfEMP1, the DBL-gamma3 domain, in cord and maternal venous blood obtained from pregnancies with various histories of P. falciparum infection. We assessed in vitro T-cell cytokine and plasma immunoglobulin G (IgG) and IgM responses to four peptides corresponding to highly conserved regions of a DBL-gamma3 domain common to central African parasite isolates. The presence of placental P. falciparum infection at delivery was associated with elevated frequencies of DBL-gamma3 peptide-specific CD3+ interleukin-10-positive T cells in cord blood, while treatment and clearance of infection prior to delivery was associated with elevated frequencies of CD3+ gamma interferon-positive T cells. DBL-gamma3 peptide-specific IgM antibodies were detected in 12 of 60 (20%) cord plasma samples from those born to mothers with P. falciparum infection during pregnancy. Consistent with polyclonal anti-PfEMP1 antibody responses that are associated with protection against pregnancy-associated malaria, the presence of maternal IgG antibodies with specificity for one of the DBL-gamma3 peptides showed a parity-dependent profile. These data demonstrate that peptides corresponding to conserved regions of the DBL-gamma3 domain of PfEMP1 are immunogenic in P. falciparum-infected mothers and their offspring.

Amino Acid Sequence↗

PubMed2005

Immunoglobulin G isotype responses to erythrocyte surface-expressed variant antigens of Plasmodium falciparum predict protection from malaria in African children.

We assessed immunoglobulin G (IgG) isotype responses to variant surface antigens (VSA) expressed on parasite-infected erythrocytes of a panel of heterologous isolates during and after acute episodes in groups of Gabonese children presenting with either mild or severe Plasmodium falciparum malaria. In the acute and convalescent phases IgG3 and IgG1 anti-VSA antibodies, respectively, predominated. In the absence of infection, the levels of both cytophilic isotypes waned, while those of IgG4 increased, particularly in those admitted with severe malaria. Prospective analyses showed significantly longer delays between malaria attacks associated both (i) with increasing IgG1 responses with specificity for VSA of isolates from children with mild malaria and (ii) with increasing IgG4 responses with specificity for VSA of isolates from children with severe malaria. These findings imply that the predictive value of prospectively measured cross-reactive VSA-specific IgG antibodies with respect to protection against malaria in African children depends both on their isotype and on their fine specificity.

Animals↗

PubMed2005

Safety and enhanced immunogenicity of a hepatitis B core particle Plasmodium falciparum malaria vaccine formulated in adjuvant Montanide ISA 720 in a phase I trial.

Highly purified subunit vaccines require potent adjuvants in order to elicit optimal immune responses. In a previous phase I trial, an alum formulation of ICC-1132, a malaria vaccine candidate comprising hepatitis B core (HBc) virus-like particle containing Plasmodium falciparum circumsporozoite (CS) protein epitopes, was shown to elicit Plasmodium falciparum-specific antibody and cellular responses. The present study was designed as a single-blind, escalating-dose phase I trial to evaluate the safety and immunogenicity of single intramuscular doses of ICC-1132 formulated in the more potent water-in-oil adjuvant Montanide ISA 720 (ICC-1132/ISA 720). The vaccine was safe and well tolerated, with transient injection site pain as the most frequent complaint. All vaccinees that received either 20 mug or 50 mug of ICC-1132/ISA 720 developed antiimmunogen and anti-HBc antibodies. The majority of volunteers in these two groups developed sporozoite-specific antibodies, predominantly of opsonizing immunoglobulin G subtypes. Peak titers and persistence of parasite-specific antibody following a single injection of the ISA 720 formulated vaccine were comparable to those obtained following two to three immunizations with alum-adsorbed ICC-1132. Peripheral blood mononuclear cells of ICC-1132/ISA 720 vaccinees proliferated and released cytokines (interleukin 2 and gamma interferon) when stimulated with recombinant P. falciparum CS protein, and CS-specific CD4(+) T-cell lines were established from volunteers with high levels of antibodies to the repeat region. The promising results obtained with a single dose of ICC-1132 formulated in Montanide ISA 720 encourage further clinical development of this malaria vaccine candidate.

Adjuvants, Immunologic↗