Authors

J Storm⁴; J Jespersen²; K Seydel¹; T Szestak⁴; M Mbewe⁵; N Chisala ⁵; P Phula⁵; C Wang²; T Taylor¹; C Moxon³; T Lavstsen²; A Craig⁴;  ¹ Blantyre Malaria Project, College of Medicine, University of Malawi, Malawi;  ² Centre for Medical Parasitology, University of Copenhagen, Denmark;  ³ Institute of Infection and Global Health, University of Liverpool, UK;  ⁴ Liverpool School of Tropical Medicine, UK;  ⁵ Malawi-Liverpool-Wellcome Trust Clinical Research Programme, Malawi

Discussion

Cerebral malaria (CM) is one of the manifestations of severe malaria and a major cause of death in children in Sub-Saharan Africa. CM is characterised by a Plasmodium falciparum infection and unarousable coma and brain swelling in children is strongly associated with fatal outcome. Post mortem studies have shown an association between brain haemorrhages and sequestration of P. falciparum infected erythrocytes (IE) to microvascular endothelium in the brain. The mechanisms linking IE sequestration to the development of CM are not fully understood, but it is clear that both host and parasite factors play important roles. The major mediator of parasite adhesion is P. falciparum erythrocyte membrane protein 1 (PfEMP1), a variant surface antigen expressed on the IE surface. Specific PfEMP1 variants have been identified in children with CM and show binding to receptors expressed on brain microvascular endothelial cells (MEC), such as endothelial protein C receptor (EPCR) and Intercellular Adhesion Molecule 1 (ICAM-1).

It remains unclear why a child develops CM at a particular time, as the vast majority of P. falciparum infections do not lead to CM. We investigated if the pathogenesis of CM is driven by parasite variants that preferentially bind brain MEC and thereby increase the recruitment of IE to the brain. We determined the cytoadherence properties of IE from children with CM, using the IE of children with uncomplicated malaria (UM) as comparator. In addition, associations between the binding phenotype and the expression of particular PfEMP1 variants with binding to the putative receptors EPCR, ICAM-1 and CD36 were assessed. During 3 malaria seasons in Malawi, IE were obtained from carefully characterised paediatric CM and UM cases. The IE were used with minimal in vitro expansion, to retain the PfEMP1 variant expressed, and binding to primary MEC, derived from brain or dermis, was determined using a micro-channel flow adhesion assay. Inhibitory antibodies and recombinant protein were used to assess the differential role of receptors and var transcripts were identified by qPCR and associated with binding phenotype.

 

The data, for the first time, provide direct evidence of preferentially binding of IE from CM patients to brain MEC. This binding is associated with specific PfEMP1 variants expressed, and provides a mechanism by which increased sequestration in the brain leads to CM.