Platelet-mediated clumping of Plasmodium falciparum infected erythrocytes is associated with high parasitemia but not severe clinical manifestations of malaria in African children.

Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
The American journal of tropical medicine and hygiene (Impact Factor: 2.74). 11/2007; 77(5):943-6.
Source: PubMed

ABSTRACT Platelet-mediated clumping of Plasmodium falciparum-infected erythrocytes is an adhesive phenotype commonly found in field isolates that has previously been associated with severe malaria. Here, clumping was assessed in 131 isolates from Malian children. The clumping phenotype was seen in 6% (N = 51) of uncomplicated malaria, 24% (N = 51) of severe malaria, and 45% (N = 29) of high parasitemia non-severe malaria isolates. Multivariate analysis indicated that clumping was strongly positively associated with parasitemia (F(1,122) = 24.1, P < 0.001) but not with disease category (F(2,122) = 1.8, P = 0.17). Therefore platelet-mediated clumping in Malian P. falciparum isolates is primarily associated with high parasitemia and not with severe clinical manifestations of malaria.

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    ABSTRACT: Platelet-mediated clumping of Plasmodium falciparum infected erythrocytes (IEs) is a frequently observed parasite adhesion phenotype. The importance of clumping in severe malaria and the molecular mechanisms behind this phenomenon are incompletely understood. Three platelet surface molecules have previously been identified as clumping receptors: CD36, globular C1q receptor (gC1qR/HABP1/p32), and P-selectin (CD62P), but the parasite ligands mediating this phenotype are unknown. The aim of this work was to develop a selection method to facilitate investigations of the molecular mechanisms of clumping in selected P. falciparum lines. Magnetic beads coated with anti-platelet antibodies were used to positively and negatively select clumping IEs from P. falciparum strains IT, HB3, 3D7 and Dd2. Clumping in all four positively selected parasite lines was abolished by antibodies to CD36, but was not affected by antibodies to gC1qR or P-selectin. Clumping positive lines showed significantly higher binding to CD36 than clumping negative lines in flow adhesion assays (strains IT, HB3 and 3D7, p<0.05 for all strains, paired t test) and static assays (strain Dd2, p<0.0001 paired t test). However, clumping negative lines IT, HB3 and 3D7 did show some binding to CD36 under flow conditions, indicating that CD36-binding is not sufficient for clumping. These data show that CD36-dependent clumping positive and negative lines can easily be selected from P. falciparum laboratory strains. CD36-binding is necessary but not sufficient for clumping, and the molecular differences between clumping positive and negative parasite lines responsible for the phenotype require further investigation.
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    Journal of Visualized Experiments 05/2013; DOI:10.3791/4316

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