• View in gallery

    Effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers. The IRBC suspensions at a hematocrit of 10%, 20%, and 30% were infused at different flow rates to maintain a constant shear stress of 5 dynes/cm2. Both IRBC rolling flux and adhesion were significantly increased as the hematocrit increased despite a decrease in the total number of IRBCs infused as a result of lower flow rates (n = 9). Error bars show the mean ± SEM. ns = not significant.

  • View in gallery

    Lack of effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBC) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers when the shear rate was kept constant. Experiments were conducted at shear rates of 500/second and 167/second (n = 3 for each shear rate). Error bars show the mean ± SEM.

  • View in gallery

    Effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers in the presence of normal uninfected erythrocytes (NRBCs) or erythrocytes that had been heat-treated to reduce deformability (HRBCs). There was a significance increase in IRBC rolling flux and adhesion in the presence of HRBCs with hematocrit, although the increase in IRBC adhesion and rolling flux at a hematocrit of 30% was significantly lower than that in the presence of NRBCs (n = 6). Error bars show the mean ± SEM.

  • View in gallery

    Effect of tumor necrosis factor-α (TNF-α) on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) at a hematocrit of 10%, 20%, and 30%. Human dermal microvascular endothelial cell monolayers were stimulated with recombinant TNF-α at a concentration if 10 ng/mL for 24 hours before the flow chamber experiments. The IRBC rolling flux and adhesion were significantly increased with hematocrit on TNF-α–stimulated endothelium. Cytokine treatment significantly increased IRBC adhesion but not rolling flux compared with untreated monolayers (n = 5). Error bars show the mean ± SEM.

  • View in gallery

    Effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers in the presence of RPMI 1640 culture medium or human AB serum. Adhesion but not rolling flux was significantly reduced when IRBCs were suspended in human AB serum compared with RPMI 1640 culture medium. However, the increase in rolling and adhesion with hematocrit was maintained in human AB serum (n = 7). Error bars show the mean ± SEM.

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ATTENUATION OF CYTOADHERENCE OF PLASMODIUM FALCIPARUM TO MICROVASCULAR ENDOTHELIUM UNDER FLOW BY HEMODILUTION

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  • 1 Department of Microbiology and Infectious Diseases and Immunology Research Group, University of Calgary, Calgary, Alberta, Canada; Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand

The cytoadherence of Plasmodium falciparum–infected erythrocytes (IRBCs) to endothelium is mediated by adhesion molecules within the physical constraints of a viscous fluid containing mostly erythrocytes. The volume fraction of erythrocytes (hematocrit) and their physical properties, such as deformability, are important properties of blood that affect cell recruitment to the vascular wall. In the present study, we examined the effect of hematocrit on IRBC rolling and adhesion on human microvascular endothelial cells in a flow chamber system in vitro. We found hematocrit to be a major determinant of IRBC/endothelial cell interactions. There was a 5-fold and 12-fold increase in IRBC rolling and adhesion, respectively, when hematocrit increased from 10% to 30%, as a result of changes in shear rate. Similar effects were seen in the presence of less deformable erythrocytes, serum proteins, and on endothelium stimulated with tumor necrosis factor-α. The results indicate that hemorheologic variations are an important determinant of the degree of cytoadherence.

INTRODUCTION

The adhesion of Plasmodium falciparum–infected erythrocytes (IRBCs) to vascular endothelium is central to the pathogenesis of P. falciparum malaria.1 An understanding of the molecular basis of the adhesive process has evolved over the past decade. What was conceived and studied as a static interaction mediated by a single endothelial receptor27 has now been shown to involve different types of dynamic adhesive interactions under physiologic flow conditions810 that mimic the events involved in leukocyte recruitment.11 Moreover, cytoadherence on microvascular endothelial cells is mediated synergistically by several adhesion molecules that appear to have different roles. The IRBCs roll on intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and P-selectin.9 The low-affinity interactions with these molecules by themselves are not sufficient for the arrest of the rolling cells, but they enhance the subsequent adhesion of almost all clinical parasite isolates tested to CD36.

What is less appreciated are the physical constraints under which cytoadherence occurs in vivo. Blood is a viscous fluid consisting of various types of cells, mainly erythrocytes, in plasma. The volume fraction of erythrocytes (hematocrit) and their physical properties, such as deformability, are important properties of blood that determine the rheology in a complex manner. Rheology in turn may affect recruitment events such as the margination of cells prior to rolling and adhesion. Indeed, the addition of erythrocytes to a suspension of leukocytes has been shown to promote leukocyte adhesion in vitro through margination or by initiating and stabilizing attachments that follow.12

In the present study, we investigated the effect of hematocrit on the adhesion of IRBCs to microvascular endothelial cells in a flow chamber assay in vitro. In addition, we determined the effect of uninfected erythrocytes that have been heat-treated to reduce their deformability and serum proteins on IRBC rolling and adhesion. We further examined the effect of hematocrit on IRBC adhesion to tumor necrosis factor-α (TNF-α)–stimulated endothelium, since levels of pro-inflammatory mediators are known to be elevated in severe P. falciparum malaria.13,14

MATERIALS AND METHODS

Parasites.

Cryopreserved parasite isolates from adult Thai patients with well-documented P. falciparum malaria were thawed and studied during the first cycle in culture as described.9 Collection of infected blood was approved by the Ethics Committee of the Faculty of Tropical Medicine, Mahidol University (Bangkok, Thailand).

Endothelial cell culture.

Human dermal microvascular endothelial cells (HDMECs) were harvested from discarded neonatal human foreskins using Type IA collagenase (Boehringer Mannheim Biochemicals, Indianapolis, IN) at a concentration of 0.5 mg/mL as described previously.9 The protocol was reviewed and approved by the Conjoint Health Research Ethics Board of the University of Calgary. The cells were maintained in endothelial basal medium (Biowhittaker, Walkerville, MD) with supplements provided by the manufacturer. Experiments were performed with cells from passage 1 to 5 on which adhesion molecule expression was shown to be stable. We and others have shown previously that resting HDMECs express CD36 and ICAM-1, and that stimulation with TNF-α for 24 hours upregulates ICAM-1 expression and induces VCAM-1 expression.9,15 In experiments to study the effect of TNF-α on cytoadherence at different hematocrits, endothelial monolayers were stimulated with the recombinant cytokine (BD BioSciences, San Jose, CA) at a concentration of 10 ng/mL for 24 hours prior to the flow chamber experiments.

Heat-damaged erythrocytes.

Erythrocytes from a normal donor were washed in RPMI 1640 medium and resuspended at a 50% hematocrit. Cells were stored at 4°C for a maximum of three weeks. At the time of the experiments, erythrocytes were washed and resuspended at a 50% hematocrit in RPMI 1640 medium. The suspension was heated to 50°C in a water bath for 15 minutes. Examination of red blood cell suspensions by phase contrast microscopy showed that heated erythrocytes displayed a spherical rather than the normal biconcave appearance.

Serum.

Human AB serum was obtained from ICN, Inc. (Costa Mesa, CA) and stored at −20°C until use.

Calculation of flow parameters.

Changes in shear stress were made by altering the volumetric flow rate according to the equation Q = τB2 W/6μ, where Q = flow rate, τ = shear stress, B = thickness of the gasket, W = width of the window, and μ = viscosity.16 The relative viscosities for red blood cells suspended in saline at a mean shear rate of 230/second were read off a published graph.17 For normal erythrocytes, the relative viscosities were 1.5, 2.2, and 3.05 for hematocrits of 10%, 20%, and 30%, respectively. Corresponding values for less deformable erythrocytes were 1.2, 2.05, and 3.7. Shear rate was calculated according to the equation shear stress = shear rate × viscosity.

Adhesive interactions under flow condition.

The IRBC-endothelial cell interactions at 5 dyne/cm2 were studied using a parallel plate flow chamber by a previously described method with modifications.9 The IRBCs from clinical parasite isolates were prepared as a 1% hematocrit suspension in RPMI 1640 medium, pH 7.2. Packed normal or heat-treated erythrocytes were added to prepare suspensions with hematocrits of 10%, 20%, and 30%. Red blood cell suspensions were infused for 4 minutes followed immediately by Hank’s balanced salt solution (HBSS) at the same flow rate. Six video monitor frames during HBSS infusion were counted for 20 seconds each, and the mean number of rolling and adherent IRBCs were quantitated as described.9 Uninfected erythrocytes at 10–30% hematocrits did not roll or adhere on endothelial monolayers under the experimental conditions used in this study.

Statistical analysis.

All data are presented as mean ± SEM. Raw data between two groups were compared by Student’s t-test for paired samples. Raw data from greater than two groups were compared by analysis of variance for paired samples, using post hoc analysis with Bonferoni’s correction for multiple comparisons. Probabilities ≤ 0.05 were considered statistically significant.

RESULTS

The effect of hematocrit on IRBC rolling and adhesion was studied with 15 randomly selected clinical parasite isolates from patients with either uncomplicated or severe P. falciparum malaria. The parasitemias of the isolates ranged from 2% to 14% (median = 5.9%). The results are therefore representative of a wide range of wild-type parasites.

Effect of hematocrit on IRBC rolling and adhesion.

We found hematocrit to be a major determinant of IRBC and endothelial cell interactions. As shown in Figure 1A, IRBC rolling flux increased from 34 ± 8 to 166 ± 44 IRBCs/minute/mm2 as hematocrit increased from 10% to 20% (P < 0.01). No further increase in rolling flux was noted as hematocrit was increased from 20% to 30%. The increase in the number of rolling cells was associated with a marked increase in the number of adherent IRBCs from 10 ± 2/mm2 at a 10% hematocrit to 74 ± 12 /mm2 at a 20% hematocrit (P < 0.001) and to 123 ± 16/mm2 at a 30% hematocrit (P < 0.001) (Figure 1B). The increases at 20% and 30% hematocrits occurred even though the total number of IRBCs infused at these values was 1.5-fold and 2-fold lower than at a 10% hematocrit, as the volume flow rates were adjusted proportionally to maintain a shear stress of 5 dynes/cm2. Results were obtained in nine separate experiments with eight different parasite isolates (parasitemia range = 4–10%).

The increase in IRBC rolling and adhesion seen in these experiments could be due either to a difference in shear rate, and thus residence time, or a change in the relative viscosity of the perfusate. To distinguish between the effects of the two parameters, separate experiments were performed at shear rates of 167/second or 500/second with three parasite isolates (parasitemia range = 6–14%). Figure 2A and 2B show that IRBC rolling and adhesion was unaffected by the increase in hematocrit when the shear rate was held constant (P > 0.05). This was true for both shear rates studied. These findings suggest that IRBC adhesion is dependent on contact duration (dictated by shear rate) and that once adherent, the IRBC-endothelial cell interaction is sufficiently stable to resist the increased tensile forces (exerted by shear stress).

Effect of heat-damaged red blood cells on IRBC rolling and adhesion at 10–30% hematocrits.

Previous studies have documented that uninfected erythrocytes in patients with acute P. falciparum malaria display reduced deformability.18,19 Since rigid erythrocytes are known to marginate,20 these cells may compete with IRBCs at the vessel wall, thereby reducing the interaction of the latter with adhesion molecules on the endothelium. The rolling and adhesion of IRBCs were therefore tested with six parasite isolates (parasitemia range = 2–9.8%) in the presence of normal or heat-damaged erythrocytes at all three hematocrits. As with normal erythrocytes, there was a significant increase in IRBC rolling and adhesion with increasing hematocrit in the presence of heated erythrocytes (Figure 3A and 3B). The rolling flux increased from 26 ± 14/minute/mm2 at a 10% hematocrit to 110 ± 40/minute/mm2 at a 20% hematocrit (P < 0.05), but did not increase further at a 30% hematocrit (98 ± 39/minute/mm2). The number of adherent IRBCs increased from 3 ± 1/mm2 at a 10% hematocrit to 22 ± 7/mm2 at a 20% hematocrit (P < 0.05) and to 29 ± 7/mm2 at a 30% hematocrit (P < 0.01). Although the effect of hematocrit on cytoadherence was maintained by heat-treated erythrocytes, the magnitude of the increase at a 30% hematocrit was significantly lower than in the presence of untreated cells (P = 0.032).

Effect of TNF-α on IRBC rolling and adhesion at 10–30% hematocrits.

We next determined if the effect of hematocrit on cytoadherence holds true on inflamed endothelium, since pro-inflammatory cytokines are produced in abundance in severe P. falciparum malaria.13,14 The results show that increased hematocrit resulted in an increase in the number of rolling cells at 20% (P < 0.05) and 30% (P < 0.05) hematocrits compared with a 10% hematocrit (Figure 4A). More importantly, the number of adherent IRBCs increased from 11 ± 2/mm2 at a 10% hematocrit to 118 ± 7/mm2 at a 20% hematocrit (P < 0.001), and increased further to 158 ± 10/mm2 at a 30% hematocrit (P < 0.01) (Figure 4B). The increase in adhesion was higher on cytokine-stimulated endothelium than on unstimulated controls at 20% (P = 0.002) and 30% (P = 0.0064) hematocrits. The results were obtained with four parasite isolates (parasitemia range = 4–10.2%) in five separate experiments.

Effect of serum on IRBC rolling and adhesion at 10–30% hematocrits.

Thus far, all data have been generated using IRBC suspensions in RPMI 1640 medium. Serum proteins such as albumin are known to adsorb to the glycocalyx of endothelial cells, forming a complex endothelial surface layer that exerts compressive forces on erythrocytes that try to penetrate it.21 The end result is the exclusion of erythrocytes from the endothelial surface layer, which diminishes the opportunity for adhesive interactions. To determine if the increase in IRBC rolling flux and adhesion with hematocrit is seen in the presence of serum proteins, IRBCs were infused in suspensions prepared with normal AB serum instead of RPMI 1640 medium. An increase in both IRBC rolling and adhesion with hematocrit was seen when IRBCs were suspended in normal AB serum (Figure 5). The IRBC rolling flux increased from 6 ± 2/minute/mm2 at a 10% hematocrit to 87 ± 14/min/mm2 at a 20% hematocrit (P < 0.05) and to 98 ± 13/minute/mm2 at a 30% hematocrit (P < 0.01). The corresponding number of adherent cells were 1 ± 0.6/mm2, 28 ± 8/mm2 (P < 0.05), and 44 ± 13/mm2 (P < 0.01). As expected, adhesion was significantly lower in serum compared with RPMI 1640 medium at all three hematocrits tested (P = 0096, 0.0110, and 0.0056, respectively). The results, obtained with six parasite isolates (parasitemia range = 2.7–14%) in seven separate experiments, indicate that the modulating effect of hematocrit on cytoadherence is not restricted to IRBC suspensions in tissue culture media.

DISCUSSION

In this study, we demonstrated for the first time that hemorheologic variations of blood can dramatically influence the degree of IRBC cytoadherence, and thus may contribute to the outcome of P. falciparum infection. An increase in hematocrit from 10% to 20% resulted in marked enhancement of both IRBC rolling and adhesion, most likely due to increased margination of IRBCs toward the endothelial monolayer. The number of rolling IRBCs did not increase further with an increase in hematocrit from 20% to 30%, while the number of adherent IRBCs continued to increase, suggesting that more rolling IRBCs were becoming arrested at the higher hematocrit. The increase in IRBC-endothelial cell interactions with increasing hematocrit appeared to be related to a decrease in shear rate as relative viscosity was increased, but was independent of shear stress. The same relationship held true on inflamed endothelium in the presence of less deformable uninfected erythrocytes and serum proteins. The beneficial effect of hemodilution with regard to IRBC adhesion is consistent with the report that increasing shear rates by the infusion of plasma reduces the number of adherent leukocytes in an ischemia/reperfusion model in cats, resulting in less vascular dysfunction.22

The question arises as to the potential clinical relevance of hemodilution in patients with P. falciparum malaria, particularly in children in whom anemia and cerebral malaria are the two major complications. There are at least two factors that need to be considered in vivo. A change in hematocrit leads to a corresponding alteration in blood viscosity, which would tend to cause blood flow to vary in an inverse direction. One of the major target organs of the hemodilution effect is the brain, where the flow rate at a 12% hematocrit has been shown to be more than two times that at a 45% hematocrit.23 By increasing cerebral blood flow, the hemodynamic conditions in an anemic individual would be less favorable for cytoadherence than in a patient with normal hemoglobin. This apparent protective advantage against cerebral IRBC sequestration must be balanced against the adverse effect of anemia on oxygen delivery to vital tissues. In animal models, the oxygen delivery index has been shown to be optimal between a 30–40% hematocrit. However, a range of optimum hematocrits in which the oxygen transport rate remains relatively constant can be maintained by variations in regional vascular resistance. The range is considerably wider for the heart and brain than for the abdominal organs, with oxygen delivery being 50–100% of the control value even with a hematocrit of 12%. In other words, the brain may be able to tolerate a much lower hematocrit without significant compromise of oxygen delivery.

A related issue is whether shear stress or shear rate is maintained in vascular beds with a change in hematocrit. In an extensive analysis of different vascular beds in rats, identical variations of shear stress (from ≈ 100 to 10 dynes/cm2) were recorded in arterioles, capillaries, and venules.24 Moreover, the study provided evidence that different vascular beds have adapted to maintaining the wall shear stress at the expense of shear rate. These experimental findings would suggest that our results of increasing IRBC adhesion with hematocrit at constant shear stress are likely to be physiologically relevant.

The results with heat-treated erythrocytes show that although these cells may marginate and thus compete with IRBCs at the vessel wall, the effect of hematocrit on IRBC rolling and adhesion was maintained in their presence. However, the significant reduction in the effect of heat-treated erythrocytes on IRBC rolling and adhesion at a 30% hematocrit compared with untreated cells suggests that uninfected erythrocytes with reduced deformability may in fact interfere with IRBC-endothelial cell interactions at this hematocrit. This apparent protective effect of rigid erythrocytes is in contrast to the reported association between decreased erythrocyte deformability and fatal outcome in severe P. falciparum malaria.19 The first point to make in this connection is that the protective effect was not observed at lower hematocrits that are likely to be more common in patients with severe P. falciparum malaria. Second, it has been proposed that the margination of rigid uninfected erythrocytes may contribute to disturbances of microcirculatory flow independently of cytoadherence.25 This process would offset any beneficial effect of rigid erythrocytes on IRBC adhesion. There are obviously a number of factors at play here, and the clinical outcome will most likely represent the balance of several disease processes. This complex issue warrants further investigation.

In summary, we have demonstrated that hematocrit, erythrocyte deformability, and serum proteins may all affect cytoadherence. Thus, the degree of cytoadherence depends not only on the cytoadherent phenotype of a particular parasite isolate and adhesion molecule expression on endothelial cells, but also on the milieu in which cytoadherence occurs. These factors must be taken into consideration when determining the overall pathogenic potential of malaria parasites.

Figure 1.
Figure 1.

Effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers. The IRBC suspensions at a hematocrit of 10%, 20%, and 30% were infused at different flow rates to maintain a constant shear stress of 5 dynes/cm2. Both IRBC rolling flux and adhesion were significantly increased as the hematocrit increased despite a decrease in the total number of IRBCs infused as a result of lower flow rates (n = 9). Error bars show the mean ± SEM. ns = not significant.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 72, 6; 10.4269/ajtmh.2005.72.660

Figure 2.
Figure 2.

Lack of effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBC) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers when the shear rate was kept constant. Experiments were conducted at shear rates of 500/second and 167/second (n = 3 for each shear rate). Error bars show the mean ± SEM.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 72, 6; 10.4269/ajtmh.2005.72.660

Figure 3.
Figure 3.

Effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers in the presence of normal uninfected erythrocytes (NRBCs) or erythrocytes that had been heat-treated to reduce deformability (HRBCs). There was a significance increase in IRBC rolling flux and adhesion in the presence of HRBCs with hematocrit, although the increase in IRBC adhesion and rolling flux at a hematocrit of 30% was significantly lower than that in the presence of NRBCs (n = 6). Error bars show the mean ± SEM.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 72, 6; 10.4269/ajtmh.2005.72.660

Figure 4.
Figure 4.

Effect of tumor necrosis factor-α (TNF-α) on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) at a hematocrit of 10%, 20%, and 30%. Human dermal microvascular endothelial cell monolayers were stimulated with recombinant TNF-α at a concentration if 10 ng/mL for 24 hours before the flow chamber experiments. The IRBC rolling flux and adhesion were significantly increased with hematocrit on TNF-α–stimulated endothelium. Cytokine treatment significantly increased IRBC adhesion but not rolling flux compared with untreated monolayers (n = 5). Error bars show the mean ± SEM.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 72, 6; 10.4269/ajtmh.2005.72.660

Figure 5.
Figure 5.

Effect of hematocrit on Plasmodium falciparum–infected erythrocytes (IRBCs) rolling flux (A) and adhesion (B) on confluent human dermal microvascular endothelial cell monolayers in the presence of RPMI 1640 culture medium or human AB serum. Adhesion but not rolling flux was significantly reduced when IRBCs were suspended in human AB serum compared with RPMI 1640 culture medium. However, the increase in rolling and adhesion with hematocrit was maintained in human AB serum (n = 7). Error bars show the mean ± SEM.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 72, 6; 10.4269/ajtmh.2005.72.660

Authors’ addresses: Christine Flatt, Sheona Mitchell, Bryan Yipp, and May Ho, Department of Microbiology and Infectious Diseases, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1. Sornchai Looareesuwan, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajvithi Road, Bangkok 10400, Thailand.

Acknowledgments: We thank Dr. Ayodeji Jeje (Department of Chemical and Petroleum Engineering, Univeristy of Calgary) and Dr. Kamala Patel (Department of Physiology and Biophysics, University of Calgary), for helpful discussions, and Dr. Caroline Lane (Valley View Family Practice Clinic, Calgary, Alberta, Canada) for providing skin specimens.

Financial support: This study was supported by a grant from the Anemia Institute of Research and Education (Ontario, Canada) and the Alberta Heritage Foundation for Medical Research (Alberta, Canada) to May Ho and Bryan Yipp.

REFERENCES

  • 1

    White NJ, Ho M, 1992. The pathophysiology of malaria. Adv Parasitol 31 :83–173.

  • 2

    Roberts DD, Sherwood JA, Spitalnik SL, Panton LJ, Howard RJ, Dixit VM, Frazier WA, Miller LH, Ginsburg V, 1985. Thrombospondin binds falciparum malaria parasitized erythrocytes and may mediate cytoadherence. Nature 318 :64–66.

    • Search Google Scholar
    • Export Citation
  • 3

    Ockenhouse CF, Tandon NN, Magowan C, Jamieson GA, Chulay JD, 1989. Identification of a platelet membrane glycoprotein as a falciparum malaria sequestration receptor. Science 243 :1469–1471.

    • Search Google Scholar
    • Export Citation
  • 4

    Berendt AR, Simmons DL, Tansey J, Newbold CI, Marsh K, 1989. Intercellular adhesion molecule-1 is an endothelial cell adhesion receptor for Plasmodium falciparum. Nature 341 :57–59.

    • Search Google Scholar
    • Export Citation
  • 5

    Ockenhouse CF, Tegoshi T, Maeno Y, Benjamin C, Ho M, Kan KE, Thway Y, Win K, Aikawa M, Lobb RR, 1992. Human vascular endothelial cell adhesion receptors for Plasmodium falciparum-infected erythrocytes: roles for endothelial leukocyte adhesion molecule 1 and vascular cell adhesion molecule1. J Exp Med 176 :1183–1189.

    • Search Google Scholar
    • Export Citation
  • 6

    Treutiger CJ, Heddini A, Fernandez V, Muller WA, Wahlgren M, 1997. PECAM-1/CD31, an endothelial receptor for binding Plasmodium falciparum-infected erythrocytes. Nat Med 3 :1405–1408.

    • Search Google Scholar
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Author Notes

Reprint requests: May Ho, Department of Microbiology and Infectious Diseases, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1, Telephone: 403-220-8516, Fax: 403-270-8520, E-mail: [email protected].
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