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Invited to attend this international conference held in Melbourne (Australia) from 16 to 20 August 2010, Dr. Fousseyni Touré, Head of the Malaria Section of the Medical Parasitology Unit of the CIRMF, presented his paper Analysis of pathogenicity of Plasmodium falciparum field isolates using a co-culture model of human endothelial cells/P.falciparum. He said that cerebral malaria is a major cause of mortality during infection by Plasmodium falciparum due to cytoadherence, related to the ability of P. falciparum-parasitized red blood cells (pRBC) to adhere to the post-capillary endothelium. The cytoadherence that causes sequestration of parasitized red blood cells causes microvessel blockages, hypoxia and secretion of proinflammatory cytokines, resulting in the destruction of the brain endothelial barrier.
Based on an in vitro co-culture model of a laboratory clone (clone 3D7 of P. falciparum) and primary human lung endothelial cells (HLEC) researchers at the Laboratory of Dr. Dominique Mazier (INSERM 511) had demonstrated that adherence of the parasite was responsible for the death of these cells by apoptosis (Pino et al. 2003).
“In collaboration with INSERM 511”, he added, “we developed this co-culture model of P. falciparum-HLEC in our laboratory at the International Centre for Medical Research in Franceville (CIRMF), Gabon. The main objective was to deepen our understanding of the pathogenicity of P. falciparum to identify new therapeutic and/or vaccine targets. The specific objective was to investigate, from isolates collected from malaria patients, a correlation between the clinical condition of the patient from whom the isolate was collected and endothelial changes induced by the isolates tested in the in vitro cyto-adherence model. We also investigated the differential expression of plasmodial genes coding for signal transduction molecules among these isolates.”
The main findings show that about 20% of plasmodial isolates collected from symptomatic children in the city of Franceville (southwestern province of Gabon) induced apoptosis of endothelial cells via cytoadherence; Minimum cytoadherence of about 200 pRBC/mm2 HLEC was necessary to induce apoptosis. Induction of HLEC apoptosis was associated with neurological signs (that is to say the apoptogenic isolates were more frequently encountered in children with neurological manifestations (prostration, coma) ( Toure et al. 2007, 2008). The transcriptome of the “apoptogenic” isolates versus the “non-apoptogenic” isolates was compared with a pan-genomic P. falciparum DNA microarray. We were able to identify at least 59 transcripts potentially involved in the induction of apoptosis in endothelial cells (Siau et al. 2007). This transcriptome is composed of ten surface antigens and enzymes involved in essential functions of the parasite such as replication. Finally, using double stranded RNA to turn off the expression of certain genes, we significantly reduced the induction of apoptosis. In total, 10 genes are directly involved in cytoadherence and/or the induction of apoptosis. These genes were termed Plasmodium apoptosis-linked pathogenicity factors (PALPFs). The prospects are: 1) To express the recombinant proteins corresponding to these PALPFs for immunological analysis with a view to developing a vaccine; 2) Screening inhibitors of signalling pathways involved in severe malaria with a view to developing new therapeutic approaches.
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