Molecular Mechanistic Insights into the Endothelial Receptor Mediated Cytoadherence of Plasmodium falciparum-Infected Erythrocytes

Ang Li,Hui Shi,Chwee Teck Lim,Kevin Shyong Wei Tan,Swee Jin Tan,Tong Seng Lim,Zhengjun Li,Jing Yin,Boon Chuan Low,Georges Snounou

doi:10.1371/journal.pone.0016929

Abstract

Cytoadherence or sequestration is essential for the pathogenesis of the most virulent human malaria species, Plasmodium falciparum (P. falciparum). Similar to leukocyte-endothelium interaction in response to inflammation, cytoadherence of P. falciparum infected red blood cells (IRBCs) to endothelium occurs under physiological shear stresses in blood vessels and involves an array of molecule complexes which cooperate to form stable binding. Here, we applied single-molecule force spectroscopy technique to quantify the dynamic force spectra and characterize the intrinsic kinetic parameters for specific ligand-receptor interactions involving two endothelial receptor proteins: thrombospondin (TSP) and CD36. It was shown that CD36 mediated interaction was much more stable than that mediated by TSP at single molecule level, although TSP-IRBC interaction appeared stronger than CD36-IRBC interaction in the high pulling rate regime. This suggests that TSP-mediated interaction may initiate cell adhesion by capturing the fast flowing IRBCs whereas CD36 functions as the ‘holder’ for providing stable binding.

Highlights

It has been observed since a century ago [1] that only early ring stage Plasmodium falciparum (P. f falciparum) infected red blood cells (IRBCs) appear in peripheral circulation whereas trophozoite and schizont stage IRBCs are sequestered within the capillaries of various organs including heart, gut, liver, lungs, kidney and brain [2,3]
CD36/TSP molecules were attached to the tips via steps of covalent bonding while the IRBCs were immobilized on glass substrates via strong interaction between glycoprotein and PHA-E lectin
An unmodified tip that had been incubated with the same fluorescent antibodies showed much weaker fluorescence on the cantilever and a totally dark tip region which indicated no nonspecific adsorption of antibodies on the tip. This confirmed the successful adsorption of receptors onto the atomic force microscopy (AFM) tips through specific surface conjugation methods and the density of the surface coated receptors was sufficient for single molecule binding detection

Summary

Introduction

It has been observed since a century ago [1] that only early ring stage Plasmodium falciparum (P. f falciparum) infected red blood cells (IRBCs) appear in peripheral circulation whereas trophozoite and schizont stage IRBCs are sequestered within the capillaries of various organs including heart, gut, liver, lungs, kidney and brain [2,3]. Such sequestration is mainly caused by the adherence of infected erythrocytes to the endothelial cells lining blood vessels, a process termed ‘cytoadherence’. Clinical studies have shown positive correlations between the level of cytoadherence in the cerebral blood vessels and the severity of the disease [4,5,6]

Methods

Results

Conclusion