Research projects our lab group

Dot plots and pie charts showing the var gene expression patterns in the pre-mosquito parasites and those obtained from the volunteers.
Expression of var genes in parasites before and after transmission to the human host. The expression pattern changes dramatically indicating a reset of virulence gene expression upon transmission.

Var gene expression in experimental human malaria infections

 

How the parasite coordinates its var gene expression in vivo is of tremendous interest and we are currently taking advantage of controlled human malaria infection (CHMI) studies to address this question. During CHMI studies either malaria-naïve or pre-exposed volunteers are infected with one lot of purified, cryopreserved NF54 or 7G8 sporozoites, the infectious mosquito stage of the parasite, provided by Sanaria, USA. Parasite-positive blood from the volunteers is immediately preserved for transcript profiling of the entire NF54/7G8 var gene repertoire either by quantitative real time PCR (qPCR) or RNA sequencing. For comparison, in vitro cultivated ‘pre-mosquito parasites’, gametocytes and sporozoites are also analysed. We aim to compare var gene expression patterns i) between different parasite stages, ii) between in vitro-cultivated parasites and those obtained from the volunteers, iii) between parasites recovered from malaria-naïve and semi-immune volunteers, iv) between in vivo samples obtained longitudinally during the course of volunteer infections, and v) between the two genetically different parasite strain used for CHMI studies. This analysis should allow us to answer if an intrinsic program of the parasite determines the expression of the major virulence factor PfEMP1 at the early onset of P. falciparum blood infections in malaria-naïve individuals, how this expression pattern is modulated by the host immunity and how the expression is controlled by the parasite.

Virulence-associated gene expression patterns in natural human malaria infections

 

Mainly children under five years of age and pregnant women from malaria-endemic regions suffer from severe malaria, but adults from areas of lower endemicity and non-immune travelers are also vulnerable to severe disease. Although severe malaria manifests as three main overlapping syndromes in children (cerebral malaria, hyperlactatemia/acidosis and severe anemia), disease symptomatology also varies according to age with more multiorgan complications and a higher fatality rate in adults. The underlying factors responsible for the different disease syndromes in children or age-related differences seen in adults remain largely unknown. To better understand the biological processes involved in host-pathogen interactions we are analysing samples i) from a Ghanaian cohort of paediatric malaria patients with accurately defined phenotypes of the different severe malaria syndromes and asymptomatic controls or ii) from returning adult travellers with varying previous malaria exposure and different clinical manifestations. We use an RNA sequencing and analysis pipeline to uncover associations of parasites gene expression (including var genes) with the different malaria syndromes, disease severity and a naïve immune status.

Heat map showing expression diefferences of PfEMP1 domains
Differential expression of var gene domains in P. falciparum parasites from first-time infected and pre-exposed adult travelers.

Dissecting the gene expression, subcellular localization and function of small variant surface antigens

In addition to PfEMP1, which certainly mediates antigenic variation and endothelial receptor binding of P. falciparum, much less is known about the small variant surface antigens families RIFIN, STEVOR and PfMC-2TM. Interestingly, they members have been localized at different subcellular sites within the infected red blood cell and are, therefore, candidates for mediating several of the patho-physiological events during malaria disease. However, a better understanding of these small variant surface protein families is necessary and may reveal new targets for intervention. To get more insight in their function, we established analytical tools for analyzing parasites obtained from malaria patients, whose gene expression and protein localization is not influenced by prolonged in vitro-cultivation. We could already show that the gene expression of RIFIN- and STEVOR-encoding genes is enhanced in vivo and that proteins of both families contribute to the surface coat of the infected red blood cell. Currently, we are characterizing the gene expression, localization and functional role of small variant surface antigen in the invasive stage, the merozoite, as well as in other life cycle stages of the parasite.

Scheme of a trophozoites (top) and schizonts with developing merozoites (bottom) showing the localization of the small variant surface antigen families RIFIN, STEVOR and PfMC-2TM as dots within the infected erythrocyte.
Localization of the small variant surface antigens RIFIN, STEVOR and PfMC-2TM during asexual blood stage development. The subcellular localization depends on the parasite stage with a predominant association with the erythrocyte membrane during the trophozoite stage (top) and an localization within the newly formed merozoites during the schizont stage (bottom).

Abteilung Zelluläre Parasitologie

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