Abstract
BackgroundAn important virulence mechanism of the malaria parasite Plasmodium falciparum is cytoadhesion, the binding of infected erythrocytes to endothelial cells in the second half of asexual blood stage development. Conventional methods to investigate adhesion of infected erythrocytes are mostly performed under static conditions, many are based on manual or semi-automated read-outs and are, therefore, difficult to standardize. Quartz crystal microbalances (QCM) are sensitive to nanogram-scale changes in mass and biomechanical properties and are increasingly used in biomedical research. Here, the ability of QCM is explored to measure binding of P. falciparum-infected erythrocytes to two receptors: CD36 and chondroitin sulfate A (CSA) under flow conditions.MethodsBinding of late stage P. falciparum parasites is measured in comparison to uninfected erythrocytes to CD36- and CSA-coated quartzes by QCM observing frequency shifts. CD36-expressing cell membrane fragments and CSA polysaccharide were coated via poly-l-lysine to the quartz. The method was validated by microscopic counting of attached parasites and of erythrocytes to the coated quartzes.ResultsFrequency shifts indicating binding of infected erythrocytes could be observed for both receptors CD36 and CSA. The frequency shifts seen for infected and uninfected erythrocytes were strongly correlated to the microscopically counted numbers of attached cells.ConclusionsIn this proof-of-concept experiment it is shown that QCM is a promising tool to measure binding kinetics and specificity of ligand-receptor interactions using viable, parasite-infected erythrocytes. The method can improve the understanding of the virulence of P. falciparum and might be used to cross-validate other methods.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1374-7) contains supplementary material, which is available to authorized users.
Highlights
An important virulence mechanism of the malaria parasite Plasmodium falciparum is cytoadhesion, the binding of infected erythrocytes to endothelial cells in the second half of asexual blood stage development
In contrast to the other species, P. falciparum-infected red blood cells adhere to vascular endothelium of postcapillary venules and to non-infected erythrocytes in the second half of their asexual replication, cycle via P. falciparum erythrocyte membrane protein 1 (PfEMP1), which is expressed on the surface of iRBCs [8, 9]
CD36 is expected to be the main receptor of iRBC adhesion as most laboratory isolates of P. falciparum, as well as clinical isolates from patients attach to this receptor [15,16,17]
Summary
An important virulence mechanism of the malaria parasite Plasmodium falciparum is cytoadhesion, the binding of infected erythrocytes to endothelial cells in the second half of asexual blood stage development. The ability of QCM is explored to measure binding of P. falciparum-infected erythrocytes to two receptors: CD36 and chondroitin sulfate A (CSA) under flow conditions. Quartz crystal microbalances (QCM) are highly sensitive sensors that can reliably weigh material in the nanogram range and are highly sensitive to changes in biomechanical properties of coupled biomaterial. A novel QCM-based assay is presented to evaluate whole cell interactions by measuring cytoadhesion of erythrocytes infected with the malaria parasite Plasmodium falciparum to endothelial cell receptors. CSA is present on other endothelial tissue where parasites might bind to it [22]
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