Physics of Parasitism

P3 - Cytoadherence of Plasmodium infected erythrocytes

Plasmodium falciparum-binding properties

Plasmodium falciparum is responsible for the majority of malaria related morbidity and mortality in humans. Of great importance for the pathology of malaria is the ability of P. falciparum infected erythrocytes (IEs) to cytoadhere to vascular endothelia. Until now, little is known concerning the kinetics and dynamics of the process of cytoadhesion.

We have recently formulated an alternative model for the process of cytoadhesion. In this model, removal of IEs from the bloodstream (tethering) occurs via the endothelial cell receptor (ECR) CD36, over which IEs subsequently move in a rolling fashion. At a later time point, due to stimulation of endothelial cells (ECs), mostly static binding to additional ECRs takes place (adhesion). The following hypotheses result from this model: 1. PfEMP1 proteins bind to CD36 via a slip-bond; the rolling phenotype results in little or no activation of ECs. Therefore, binding favours the development of mild malaria. 2. PfEMP1 proteins bind to other ECRs via catch binding, resulting in stable binding and activation of ECs. Therefore, binding favours the development of severe malaria. 3. Knobs on the surface of IEs are essential to adhere to the endothelium even under febrile conditions. Thus, there is an evolutionary pressure on the formation of knobs. 4. VAR2CSA (responsible for pregnancy-associated malaria) can bind only in the presence of the low shear forces prevailing in the placenta; therefore, binding to the endothelium of other organs does not occur. 5. Synthetic peptides based on sequences of the binding epitopes can inhibit the activation of ECs.

By combining transgenic cells and plasmodia expressing defined ECRs or PfEMP1s and 1. atomic force microscopy (AFM) (to distinguish between single and multiple bindings and between slip and catch binding mechanisms) in combination with the determination of calcium signalling, 2. surface acoustic wave biosensor and isothermal titration calorimetry (to characterise binding (association and dissociation), 3. laminar flow system (to characterise binding phenotype), 4. AFM/electron and immunofluorescence microscopy (to visualise interaction), and 5. synthesis of peptide-based inhibitors (iterative improvement by evolutionary algorithm), hypotheses raised will be investigated.