Cytoadherence and genotype of Plasmodium falciparum strains from symptomatic children in Franceville, southeastern Gabon

Comparison of apoptosis in human primary pulmonary endothelial cells and a brain microvascular endothelial cell line co-cultured with Plasmodium falciparum field isolates

BACKGROUND

Plasmodium falciparum infection can progress unpredictably to severe forms including respiratory distress and cerebral malaria. The mechanisms underlying the variable natural course of malaria remain elusive.

METHODS

The cerebral microvascular endothelial cells-D3 and lung endothelial cells both from human were cultured separately and challenged with P. falciparum field isolates taken directly from malaria patients or 3D7 strain (in vitro maintained culture). The capacity of these P. falciparum isolates to induce endothelial cell apoptosis via cytoadherence or not was then assessed.

RESULTS

Overall, 27 P. falciparum isolates were collected from patients with uncomplicated malaria (n = 25) or severe malaria (n = 2). About half the isolates (n = 17) were able to bind brain endothelial cells (12 isolates, 44%) or lung endothelial cells (17 isolates, 63%) or both (12 isolates, 44%). Sixteen (59%) of the 27 isolates were apoptogenic for brain and/or lung endothelial cells. The apoptosis stimulus could be cytoadherence, direct cell-cell contact without cytoadherence, or diffusible soluble factors. While some of the apoptogenic isolates used two stimuli (direct contact with or without cytoadherence, plus soluble factors) to induce apoptosis, others used only one. Among the 16 apoptogenic isolates, eight specifically targeted brain endothelial cells, one lung endothelial cells, and seven both.

CONCLUSION

These results indicate that the brain microvascular cell line was more susceptible to apoptosis triggered by P. falciparum than the primary pulmonary endothelial cells and may have relevance to host-parasite interaction.

Specific receptor usage in Plasmodium falciparum cytoadherence is associated with disease outcome

Our understanding of the basis of severe disease in malaria is incomplete. It is clear that pathology is in part related to the pro-inflammatory nature of the host response but a number of other factors are also thought to be involved, including the interaction between infected erythrocytes and endothelium. This is a complex system involving several host receptors and a major parasite-derived variant antigen (PfEMP1) expressed on the surface of the infected erythrocyte membrane. Previous studies have suggested a role for ICAM-1 in the pathology of cerebral malaria, although these have been inconclusive. In this study we have examined the cytoadherence patterns of 101 patient isolates from varying clinical syndromes to CD36 and ICAM-1, and have used variant ICAM-1 proteins to further characterise this adhesive phenotype. Our results show that increased binding to CD36 is associated with uncomplicated malaria while ICAM-1 adhesion is raised in parasites from cerebral malaria cases.

Inhibition of Plasmodium falciparum field isolates-mediated endothelial cell apoptosis by Fasudil: therapeutic implications for severe malaria

Plasmodium falciparum infection can abruptly progress to severe malaria, a life-threatening complication resulting from sequestration of parasitized red blood cells (PRBC) in the microvasculature of various organs such as the brain and lungs. PRBC adhesion can induce endothelial cell (EC) activation and apoptosis, thereby disrupting the blood-brain barrier. Moreover, hemozoin, the malarial pigment, induces the erythroid precursor apoptosis. Despite the current efficiency of antimalarial drugs in killing parasites, severe malaria still causes up to one million deaths every year. A new strategy targeting both parasite elimination and EC protection is urgently needed in the field. Recently, a rho-kinase inhibitior Fasudil, a drug already in clinical use in humans for cardio- and neuro-vascular diseases, was successfully tested on laboratory strains of P. falciparum to protect and to reverse damages of the endothelium. We therefore assessed herein whether Fasudil would have a similar efficiency on P. falciparum taken directly from malaria patients using contact and non-contact experiments. Seven (23.3%) of 30 PRBC preparations from different patients were apoptogenic, four (13.3%) acting by cytoadherence and three (10%) via soluble factors. None of the apoptogenic PRBC preparations used both mechanisms indicating a possible mutual exclusion of signal transduction ligand. Three PRBC preparations (42.9%) induced EC apoptosis by cytoadherence after 4 h of coculture (“rapid transducers”), and four (57.1%) after a minimum of 24 h (“slow transducers”). The intensity of apoptosis increased with time. Interestingly, Fasudil inhibited EC apoptosis mediated both by cell-cell contact and by soluble factors but did not affect PRBC cytoadherence. Fasudil was found to be able to prevent endothelium apoptosis from all the P. falciparum isolates tested. Our data provide evidence of the strong anti-apoptogenic effect of Fasudil and show that endothelial cell-P. falciparum interactions are more complicated than previously thought. These findings may warrant clinical trials of Fasudil in severe malaria management.

Relationship between in vivo synchronicity of Plasmodium falciparum and allelic diversity

Plasmodium falciparum cells tend to grow in synchronicity during their cyclic intraerythrocytic development in vivo. Both host and parasite factors appear to be involved in this synchronization. We examined the link between mixed-allelic-family P. falciparum infection and synchronicity in parasitized red blood cells (PRBC) from symptomatic children. The distribution of rings and trophozoites in each PRBC sample was determined by standard microscopy. P. falciparum was genotyped by using a polymerase chain reaction (PCR) targeting three loci (merozoite surface proteins (MSP) 1 and 2, and 175-kD erythrocyte binding antigen (EBA), allowing us to distinguish parasite clones belonging to a single-allelic family (SAF) and those belonging to a mixed-allelic family (MAF). Parasite development was considered synchronous when peripheral blood contained at least 95% of rings or 95% of trophozoites. Parasite development was synchronous in 22 (21.2%) of the 104 children studied. Twenty (90.9%) of these infections were SAF and two (9.1%) were MAF. Rings and trophozoites predominated in respectively 12 (60%) and 8 (40%) SAF infections. Respectively 17.1% and 82.9% of the 82 asynchronous cases corresponded to SAF and MAF infection. Parasite synchronicity was therefore significantly related to single-allelic-family infection (p<2x10(-10)). Twenty different MSP-1 alleles and thirteen different MSP-2 alleles were identified. Only three isolates from patients with SAF infection comprised a single allele or genotype, the other isolates harboring at least two alleles. The mean number of alleles or clones was respectively 3.0 and 10.0 in SAF and MAF infection. These results reflect the allelic diversity of the MSP loci and show that SAF infection can correspond to multiple parasite clones (or genotypes) but, in general, fewer than in MAF infection (p<or=0.0007). These results confirm the extensive polymorphism of P. falciparum vaccine candidates MSP-1 and -2 in southeastern Gabon and demonstrate that parasite synchronicity in vivo is strongly associated with single-allelic-family infection.