Sequestration Of Infected Red Blood Cells Research Articles

Identification of Plasmodium falciparum-specific protein PIESP2 as a novel virulence factor related to cerebral malaria

Cerebral malaria (CM) is the most severe complication caused by Plasmodium falciparum infection. The pathophysiological changes caused by parasite virulence factors and the human immune response to parasites contribute to CM. To date, very few parasite virulence proteins have been found to participate in CM. Here, we employed comparative genomics analysis and identified parasite-infected erythrocyte specific protein 2 (PIESP2) to be a CM-related protein. We conducted further experimental investigations and found that PIESP2 is an immunogenic protein. PIESP2 expression begins at the early trophozoite stage and progressively increases with parasite development. Although PIESP2 proteins mainly reside within infected red blood cells (IRBCs), some of them are present on the IRBC surface at the pigmented stage. Moreover, blockage of PIESP2 by antiserum apparently inhibited the adhesion of IRBCs to brain microvascular endothelial cells (BMECs). Western blot analysis detected the binding of PIESP2 to BMECs. Transcriptional analysis revealed that the binding of PIESP2 to BMECs can increase the expression of genes involved in the inflammatory response but decrease the expression of genes related to the anchoring junction. Overall, PIESP2 might be associated with CM by mediating the sequestration of IRBCs, inducing the inflammation response, and impairing the integrity of blood–brain barrier.

The <i>Plasmodium falciparum</i>-Specific Protein PIESP2 Can Mediate the Sequestration of Infected Erythrocytes to Brain Microvascular Endothelial Cells (BMECs) and Induce Inflammatory Response in BMECs

Background: Cerebral malaria (CM) is the most severe complication caused by Plasmodium falciparum infection. The pathophysiological changes caused by parasite virulent factors and human immune response to parasites contribute to CM. To date, very few parasite virulent proteins have been found to participate in CM. Identifying new parasite proteins involved in CM may provide new directions for possible intervention. Methods: Comparative genomic analysis was performed and parasite-infected erythrocyte specific protein 2 (PIESP2) was identified to be a CM-related candidate protein. The immunogenic property of PIESP2 was investigated. Its expression and localization in infected red blood cells (IRBCs) during intraerythrocytic stage were characterized. Adhesion assay and RNA-seq were adopted to evaluate the role of PIESP2 in the development of CM. Findings: PIESP2 is an immunogenic protein. Its expression begins at the early trophozoite stage and progressively increases with parasite development. PIESP2 mainly resides inside IRBCs but few of them are present on IRBC surface at the late trophozoite stage. Blockage of PIESP2 by antiserum apparently inhibited the adhesion of IRBCs to brain microvascular endothelial cells (BMECs). Moreover, PIESP2 could directly bind to BMECs, subsequently leading to an increase in the expression of genes involved in inflammatory response in BMECs and a decrease in the expression of genes related to anchoring junction. Interpretation: The P. falciparum specific protein PIESP2 may contribute to CM by mediating the sequestration of IRBCs to BMECs, inducing inflammatory response and impairing the integrity of the blood–brain barrier. Funding Statement: This work was supported by a grant from the National Natural Science Foundation of China (Grant No. 31600615). Declaration of Interests: The authors declare that they have no conflict of interest. Ethics Approval Statement: Ethical approval was given by the First Affiliated Hospital Ethics Committee of Fourth Military Medical University with reference number KY20163289-1. All experimental procedures were performed in accordance with relevant institutional and national guidelines and approved by the Institutional Animal Care and Use Committee of Fourth Military Medical University.

Cross‐presentation of malaria antigen by brain microvessels: why CD8+ T cells are critical for the pathogenesis of experimental cerebral malaria

Cross‐presentation of malaria antigen by brain microvessels: why <scp>CD</scp>8⁺ T cells are critical for the pathogenesis of experimental cerebral malaria

A Maurer's cleft–associated protein is essential for expression of the major malaria virulence antigen on the surface of infected red blood cells

The high mortality of Plasmodium falciparum malaria is the result of a parasite ligand, PfEMP1 (P. falciparum) erythrocyte membrane protein 1), on the surface of infected red blood cells (IRBCs), which adheres to the vascular endothelium and causes the sequestration of IRBCs in the microvasculature. PfEMP1 transport to the IRBC surface involves Maurer's clefts, which are parasite-derived membranous structures in the IRBC cytoplasm. Targeted gene disruption of a Maurer's cleft protein, SBP1 (skeleton-binding protein 1), prevented IRBC adhesion because of the loss of PfEMP1 expression on the IRBC surface. PfEMP1 was still present in Maurer's clefts, and the transport and localization of several other Maurer's cleft proteins were unchanged. Maurer's clefts were altered in appearance and were no longer found as close to the periphery of the IRBC. Complementation of mutant parasites with sbp1 led to the reappearance of PfEMP1 on the IRBC surface and the restoration of adhesion. Our results demonstrate that SBP1 is essential for the translocation of PfEMP1 onto the surface of IRBCs and is likely to play a pivotal role in the pathogenesis of P. falciparum malaria.

Plasmodium falciparum Cytoadherence to Human Placenta: Evaluation of Hyaluronic Acid and Chondroitin 4-Sulfate for Binding of Infected Erythrocytes

Valiyaveettil, M., Achur, R. N., Alkhalil, A., Ockenhouse, C. F., and Gowda, D. C. 2001. Plasmodium falciparum cytoadherence to human placenta: Evaluation of hyaluronic acid and chondroitin 4-sulfate for binding of infected erythrocytes. Experimental Parasitology99, 57–65. Chondroitin 4-sulfate (C4S) is known to mediate the adherence of Plasmodium falciparum infected red blood cells (IRBCs) to human placenta. Recently, hyaluronic acid (HA) has also been reported to bind IRBCs, and HA has been suggested as an additional receptor for the sequestration of IRBCs in the placenta. In this study, we assessed the adherence of 3D7 parasite strain, which has been reported to bind both C4S and HA, using highly purified clinical grade rooster comb HA, Streptococcus HA, several preparations of human umbilical cord HA (hucHA), and bovine vitreous humor HA (bvhHA). While all hucHA preparations and bvhHA bound with moderate to high density to IRBCs, the rooster comb and bacterial HAs did not bind IRBCs. IRBCs binding to the hucHA and bvhHA could be abolished by pretreatment with testicular hyaluronidase but not with Streptomyces hyalurolyticus hyaluronidase, suggesting that IRBC binding to hucHA and bvhHA was due to chondroitin sulfate (CS) contaminants in HAs. Compositional analysis confirmed the presence of CS in both hucHA and bvhHA. The CSs present in these commercial hucHA and bvhHA samples were isolated, characterized, and studied for their ability to bind IRBCs. The data suggested that IRBC adherence to hucHA and bvhHA was mediated by the CS present in these samples. However, our data did not exclude the possibility of a minor population of distinct parasite subtype adhering to HA and further studies using pure HA conjugated to proteins or lipids and placental parasite isolates should clarify whether HA is an in vivo receptor for IRBC adherence.

Microvascular hemodynamics and in vivo evidence for the role of intercellular adhesion molecule-1 in the sequestration of infected red blood cells in a mouse model of lethal malaria.

The cytoadherence of infected red blood cells (IRBCs) to the vascular endothelium is the major cause of IRBC sequestration and vessel blockage in the cerebral form of human malaria. Among the rodent models of malaria, Plasmodium yoelii 17XL-infected mice show many similarities with the human cerebral malaria caused by P. falciparum. In both, the sequestration of IRBCs in the brain vessels is secondary to the cytoadherence of IRBCs to the vascular endothelium. Similar to P. falciparum infection in the human but in contrast to P. berghei ANKA infection in mice, P. yoelii 17XL results in little, if any, accumulation of monocytes in the brain. In vivo microcirculatory studies reported here were designed to further understand the hemodynamic aspects and mechanisms underlying cytoadherence of IRBCs in the P. yoelii model using the easily accessible cremaster muscle vasculature. The results show significant decreases in arteriovenous red blood cell velocities (Vrbc) and wall shear rates in the microcirculation of P. yoelii-infected mice, with a maximal decrease occurring in small-diameter postcapillary venules, the main sites of cytoadherence. This reflects contributions from IRBC cytoadherence as well as from increased rigidity of parasitized red blood cells. No cytoadherence is observed in arterioles of the infected mice despite decreased wall shear rates, indicating that endothelial receptors for cytoadherence are restricted to venules. Infusion of a monoclonal antibody (MAb) against the intercellular adhesion molecule-1 (ICAM-1) resulted in significant increases in both arteriolar and venular Vrbc and wall shear rates, accompanied by detachment of adhered IRBCs at some venular sites. The peripheral blood smears taken after the MAb infusion showed a distinct increase in the percentage of schizonts, again indicating detachment and/or prevention of cytoadherence. An MAb against the vascular cell adhesion molecule-1 (VCAM-1) as well as an irrelevant control antibody had no effect on these parameters. These results provide the first in vivo microcirculatory evidence indicating involvement of ICAM-1, but not of VCAM-1, in the sequestration of IRBCs in a rodent model of cerebral malaria.