Var gene diversity and their serological recognition by naturally exposed individuals

Plasmodium falciparum causes the worst form of human malaria and leads to 1-2 million deaths annually, most of them children below the age of 5 living in subsaharan Africa. Morbidity varies from asymptomatic infections with no symptoms to severe malaria accompanied by organ failure, severe anemia and coma. Most of these clinical presentations are associated with sequestration of infected red blood cells (iRBC) on host endothelium. By attaching the parasitized erythrocyte to host receptors such as CD36, ICAM or CSA the parasite prevents the cell from being cleared by the spleen and therefore prolongs its own survival. A key protein involved in this process is the variant surface antigen Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) which is a parasite derived protein transported to the RBC surface to mediate cytoadherence. With this process exposes the parasite itself to the host immune system leading to the production of specific antibodies. In order to evade this host immune response the parasite undergoes antigenic variation by switching to another member of the same protein family. PfEMP1 is encoded by approximately 60 var genes per haploid genome and is expressed at the surface in a mutually exclusive manner, i.e. only 1 of the 60 proteins is expressed and exposed at any one time whilst the others remain silenced. Protection against severe malaria is thought to be mediated to a large degree by the piecemeal acquisition of anti-PfEMP1 antibodies during early childhood, since adults still get infected but rarely develop severe malaria symptoms. Recent observations suggest that not all PfEMP1 proteins expressed by a parasite are equally virulent, but only a subset of distinct var genes might render a parasite more pathogenic than parasites expressing different var gene variants. To generate potential anti-severe disease interventions members of this particular subset need to be identified. To date, only 6 studies have been published investigating the repertoire of expressed var genes in vivo. We have further used samples collected in Papua New Guinea from a case control study and analyzed var transcripts by RT-PCR followed by cloning and sequencing. We determined the 3 main groups of 5’UTR and analysed the data with respect to the clinical presentation of the children they were collected from. The detected number of different var group B and C transcipts was not significantly different between asymptomatic, mild or severe malaria cases, whereas an increase of group A var genes was observed in symptomatic cases when compared to children without any malaria symptoms. We identified an amino acid substitution mainly occurring in asymptomatic children with high parasitemia that might influence the binding affinity of parasites expressing these variants. However, using phylogenetic analyses we were not able to identify other distinct var genes or subsets associated with severe malaria. Blasting DBL1α domains against the 3D7 genome to obtain information on the upstream region was found to be suitable for group A var genes only, whereas 28% of group B and 62% of group C sequences were assigned to the wrong subgroup using this method. Even though we observed a 7% sequence overlap, bioinformatic analyses estimated the var gene repertoire in this region of PNG to be unlimited. It has previously been shown, that isolates causing severe disease are recognized more frequently than those causing mild malaria. In the second part of this thesis, we wanted to obtain information on the importance of distinct PfEMP1 domains in the recognition by the host immune system. For that purpose, fragments of 2 representative var genes shown to be associated with severe malaria were recombinantly expressed in E.coli and analyzed for their recognition by naturally exposed sera of different origin. Analysis of synthetic peptides using the same sera served to complement the results of ELISAs using recombinant proteins if expression of distinct domains was not possible. ELISA and Western blot analysis determined that 3 recombinant fragments and 2 synthetic peptides harbor epitopes that might play a role in the generation of protective antibodies. However, since sample size was small further investigations are required to confirm these findings. In the third part of this thesis, we tested the usefulness of the GeneMapper® analysis software to genotype var genes. It has been successfully established for genotyping the polymorphic marker gene msp2 and since var genes also show some length polymorphism it was investigated whether this technique could replace tedious cloning and sequencing approaches, used so far to dissect var gene diversity. Therefore, purified PCR products of UTR-DBL domains generated during the sequence analysis were reamplified with fluorescently labeled DBL-specific primers and analyzed by GeneMapper®. The results were then compared to the sequencing data. GeneMapper® sizing was highly accurate with a mean deviation of 1bp and showed a high consistency with sequencing data. Furthermore, GeneMapper® detected 141 sequences which were not identified with the sequencing approach, whereas vice verca, this was only the case for 16 sequences. However, a significant proportion of var genes could not be distinguished because the analyzed DBL domains were identical in size. Despite this shortcoming, we belive that GeneMapper® would greatly facilitate the analysis of expressed var genes and their dynamics

Efficacy of sulfadoxine-pyrimethamine in Tanzania after two years as first-line drug for uncomplicated malaria: assessment protocol and implication for treatment policy strategies.

BACKGROUND\ud \ud Systematic surveillance for resistant malaria shows high level of resistance of Plasmodium falciparum to sulfadoxine-pyrimethamine (SP) across eastern and southern parts of Africa. This study assessed in vivo SP efficacy after two years of use as an interim first-line drug in Tanzania, and determined the rates of treatment failures obtained after 14 and 28 days of follow-up.\ud \ud METHODS\ud \ud The study was conducted in the Ipinda, Mlimba and Mkuranga health facilities in Tanzania. Children aged 6-59 months presenting with raised temperature associated exclusively with P. falciparum (1,000-100,000 parasites per microl) were treated with standard dose of SP. Treatment responses were classified according to the World Health Organization (WHO) definition as Adequate Clinical and Parasitological Response (ACPR), Early Treatment Failure (ETF), Late Clinical Failure (LCF) and Late Parasitological Failure (LPF) on day 14 and day 28.\ud \ud RESULTS\ud \ud Overall 196 (85.2%) of 230 patients had ACPR on day 14 but only 116 (50.9%) on day 28 (57.7% after excluding new infections by parasite genotyping). Altogether 21 (9.1%) and 13 (5.7%) of the 230 patients assessed up to day 14 and 39 (17.1%) and 55 (24.1%) of the 228 followed up to day 28 had clinical and parasitological failure, respectively.\ud \ud CONCLUSION\ud \ud These findings indicate that SP has low therapeutic value in Tanzania. The recommendation of changing first line treatment to artemether + lumefantrine combination therapy from early next year is, therefore, highly justified. These findings further stress that, for long half-life drugs such as SP, establishment of cut-off points for policy change in high transmission areas should consider both clinical and parasitological responses beyond day 14

Coherent Activity between Brain Regions that Code for Value is Linked to the Malleability of Human Behavior

Brain activity in medial prefrontal cortex (MPFC) during exposure to persuasive messages can predict health behavior change. This brain-behavior relationship has been linked to areas of MPFC previously associated with self-related processing; however, the mechanism underlying this relationship is unclear. We explore two components of self-related processing – self-reflection and subjective valuation – and examine coherent activity between relevant networks of brain regions during exposure to health messages encouraging exercise and discouraging sedentary behaviors. We find that objectively logged reductions in sedentary behavior in the following month are linked to functional connectivity within brain regions associated with positive valuation, but not within regions associated with self-reflection on personality traits. Furthermore, functional connectivity between valuation regions contributes additional information compared to average brain activation within single brain regions. These data support an account in which MPFC integrates the value of messages to the self during persuasive health messaging and speak to broader questions of how humans make decisions about how to behave

Brain Activity in Self- and Value-Related Regions in Response to Online Antismoking Messages Predicts Behavior Change

In this study, we combined approaches from media psychology and neuroscience to ask whether brain activity in response to online antismoking messages can predict smoking behavior change. In particular, we examined activity in subregions of the medial prefrontal cortex linked to self- and value-related processing, to test whether these neurocognitive processes play a role in message-consistent behavior change. We observed significant relationships between activity in both brain regions of interest and behavior change (such that higher activity predicted a larger reduction in smoking). Furthermore, activity in these brain regions predicted variance independent of traditional, theory-driven self-report metrics such as intention, self-efficacy, and risk perceptions. We propose that valuation is an additional cognitive process that should be investigated further as we search for a mechanistic explanation of the relationship between brain activity and media effects relevant to health behavior change

Who Likes to be Reachable? Availability Preferences, Weak Ties, and Bridging Social Capital

In this paper, we investigate how individual differences in availability preferences are related to (1) self-reported quality of interaction with strong and weak ties and (2) perceptions of bridging social capital. We employed experience sampling methods and collected data over the course of two weeks—combined with surveys at baseline and endpoint, from a random sample of college students (N = 154). We show that individuals who prefer to be more available to others report more rewarding interactions with weak ties. Furthermore, we demonstrate how the quality of weak tie interactions mediates a positive relationship between availability preferences and bridging social capital. We conclude by discussing the relationships between availability, interaction quality, and bridging social capital. We propose availability preferences as a key construct to be considered in future research

Langue allemande

Falk Bretschneider Cours de langue appliquée aux sciences sociales et humaines Compte rendu non communiqué. Falk Bretschneider et Marelke König Lire l’allemand d’hier : introduction aux sources de l’histoire moderne et contemporaine allemande et à la paléographie (en coopération avec l’Institut historique allemand) Compte rendu non communiqué. Nicole Reinhardt Cours de traduction de l’allemand Enseignement annulé

Analysis of Plasmodium falciparum var Genes Expressed in Children from Papua New Guinea

Background The variable antigen P. falciparum erythrocyte membrane protein-1 (PfEMP1) is a major virulence factor in malaria. A large number of var genes encode PfEMP1, and we hypothesized that a restricted PfEMP1 repertoire determines clinical disease presentation. We conducted a case-control study in Papua New Guinea and analyzed transcribed var genes in naturally infected children. Methods var messenger RNA was isolated from 78 children with asymptomatic, mild, or severe malaria. We prepared complementary DNA from the upstream region into the DBL1α domain and picked, on average, 20 clones for sequencing. Results Twenty-five percent of centrally located var genes were shared between children, whereas only 5% of subtelomeric genes were shared, indicating lower diversity in the former group. Linkage between group B or C var upstream sequences and DBL1α groups was not observed, which impeded prediction by DBL1α analysis. A higher proportion of var group A sequences was detected in symptomatic malaria, and a subgroup of frequently encountered var genes with complex head structure seems to be associated with severe malaria. A subset of var group C genes was frequently expressed in older children with asymptomatic high levels of parasitemia. Conclusion Despite this vast diversity, restricted disease-associated var genes were identified and might be used for innovative interventions based on PfEMP

Comparison of PCR-RFLP and Genescan-based genotyping for analyzing infection dynamics of Plasmodium falciparum.

Parameters describing the infection dynamics of Plasmodium falciparum are important determinants of the potential impact of interventions and are potential outcome measurements for malaria intervention trials. Low parasite densities, periodic sequestration of parasites, and the presence of multiple concurrent infections make it essential to use molecular techniques to estimate the force of infection and duration of infections in endemic areas. We now compare two approaches for tracking individual genotypes of the highly polymorphic merozoite surface protein 2: 1) fluorescence-labeled polymerase chain reaction (PCR) and GeneScan-sizing and 2) restriction fragment length polymorphism (RFLP). We analyze samples from a longitudinal field study in Ghana and use statistical approaches that allow for imperfect detectability. The two methods gave broadly similar estimates of parasite dynamics, but GeneScan is more precise and can achieve a higher throughput. The analysis of parasite dynamics indicated an average duration of infection of 210 days by GeneScan versus 152 days by PCR-RFLP in the study population in Kassena-Nankana, Northern Ghana. This reflects the good performance of GeneScan-based genotyping for studies of parasite infection dynamics