Malaria immunity targets team (TARGETS)
Research in brief
Research in the TARGETS team is focused on a family of "sticky" proteins known as the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1). P. falciparum is the most pathogenic malaria parasite and a major cause of morbidity and mortality among children in sub-Saharan Africa. The virulence of P. falciparum has been linked to its expression of PfEMP1 on the surface of infected erythrocytes that enable the parasites to "stick" to capillaries of the host thereby avoiding removal by the spleen (Fig. 1).
Each parasite has 60 genes encoding different versions of PfEMP1 and a switch in surface display of these proteins enable the parasite to evade the immune system. Current research projects include in vitro molecular and immunological characterization of PfEMP1 proteins associated with severe malaria in young children.
The pathogenesis of P. falciparum malaria is closely associated with the ability of PfEMP1 proteins to adhere to host endothelial cells, a process that leads to tissue-specific inflammation, circulatory obstruction and organ dysfunction (Hafalla et al. 2011).
We originally identified a particular subset, group A, of PfEMP1 molecules as linked to development of severe malaria in children infected by P. falciparum (Jensen et al. 2004). The receptor specificity of these and other PfEMP1 proteins is determined by their constituent DBL and CIDR domains.
Particular subtypes of DBL and CIDR domains are found in short tandem domain cassettes (DC) shared by different parasites (Rask et al. 2010). Two such cassettes (DC8 and DC13) found in group B/A and group A PfEMP1 proteins were recently implicated in the pathogenesis of cerebral malaria and shown to bind the endothelial protein C receptor (EPCR, se the DISCOVERY team page ) (Avril et al. 2012, Lavstsen et al. 2012).
Cerebral malaria develops in a subset of P. falciparum-infected patients and is a major contributor to malaria associated mortality and to short or long-term neurological complications (Hafalla et al. 2011). The mechanisms underlying the development of cerebral malaria remain unclear but are believed to involve particular subsets of PfEMP1 molecules like DC8 and DC13, accumulation of infected erythrocytes in the cerebral microvasculature, alterations in cytokine and chemokine homeostasis and inflammation.
A study done in Malawian children with cerebral malaria showed a decreased expression of EPCR, while ICAM-1 expression was increased (Moxon et al. 2013, Turner et al. 2013), but infected erythrocytes selected for expression of DC8 or DC13 by panning on cerebral endothelial cells do not to bind to ICAM-1 (Avril et al. 2012, Turner et al. 2013).
By contrast, we showed in a recent publication that infected erythrocytes expressing Group A PfEMP1 proteins containing another domain cassette (DC4) adhere specifically to ICAM-1. The binding capacity of DC4 was mapped to the DBLβ domain and DC4 was found to be a target of broadly cross-reactive and adhesion-inhibitory human IgG (Bengtsson et al. 2013).
Research projects include in vitro molecular and immunological characterization of PfEMP1 proteins associated with severe malaria in young children and are based on our current working hypothesis of cerebral malaria development.
The initial binding of P. falciparum-infected erythrocytes expressing DC8 and DC13 PfEMP1 to EPCR on brain endothelial cells is suggested to interfere with the activation of cytoprotective and anti-inflammatory pathways leading to a decreased expression of both throbomodulin and EPCR with concomitant increased expression of ICAM-1 on brain endothelium. This could allow for subsequent sequestration of a second wave of ICAM-1-binding parasites.
We have identified a conserved epitope in group A PfEMP1, which is linked to the binding of infected erythrocytes to ICAM-1 and predicted as a molecular marker of infected erythrocytes causing severe disease. To further elucidate the importance of this motif and ICAM-1 in severe and cerebral malaria we work on:
- Structural characterization of the PfEMP1::ICAM-1 interaction (UCPH2016, Novo Nordisk Fonden).
- Molecular and bioinformatics assessment of the motif as a marker of ICAM-1 adhesion (Novo Nordisk Fonden and DANIDA).
- The involvement of PfEMP1 harbouring the motif in development of severe/cerebral malaria in P. falciparum-infected individuals (Novo Nordisk Fonden and DANIDA).
- Assessing the role of anti-motif antibodies in protecting individuals from developing severe malaria (Novo Nordisk Fonden and DANIDA).
- Host cell responses to binding of parasite lines expressing different PfEMP1 with and without the ICAM-1 binding motif (Oda and Hans Svenningsens Fond, Danish Council for Independent Research│Medical Sciences).
- Discovery and characterization of additional PfEMP1-brain endothelial receptor interactions utilized by parasites expressing the ICAM-1 binding motif (EVIMalaR).
The TARGETS team
The members of the TARGETS team (see a list of team members) cover a wide range of skills within malariology, immunology, molecular and structural biology. The team is involved in a number of national and international research collaborations, e.g., CoNext and MAVARECA-II.
Our research is supported by major grants from the UCPH2016 programme of Excellence, Oda og Hans Svenningens Fond, and the Novo Nordisk Foundation. Recently our group received funding from the Danish Council for Independent Research│Medical Sciences (DFF-4004-00032) to dissect the role of a newly discovered binding epitope associated with cerebral malaria.
Training and supervision
We welcome graduate and undergraduate students with a background in Health & Medical Sciences and Natural Sciences to do their project with the TARGETS team.
Techniques used include genetic engineering, DNA sequencing, protein expression and purification, crystallography, biosensor assays, Luminex assays, flow cytometry, hybridoma techniques, real-time quantitative PCR, flow based cellular adhesion assays, manipulation and culturing of P. falciparum malaria parasites. We do field work at Hohoe Municipal Hospital in the Volta Region of Ghana.
For more information about this team, please contact the TARGETS team leader