Evidence of Endothelial Activation in Asymptomatic Plasmodium falciparum Parasitemia and Effect of Blood Group on Levels of von Willebrand Factor in Malaria

Abstract

Background: Endothelial activation may contribute to development of severe disease from Plasmodium falciparum infection, but optimal markers of endothelial activation in severe malaria, the extent of endothelial activation in asymptomatic infection, and the effect of blood group O on endothelial activation have not been defined.

Methods: Serum levels of 3 markers of endothelial activation-von Willebrand factor (VWF), soluble intercellular adhesion molecule-1 (sICAM-1), and soluble vascular cell adhesion molecule-1 (sVCAM-1)-were assessed in Ugandan children with cerebral malaria (CM) (n = 86), children with uncomplicated malaria (UM) (n = 81), and community children (CC) (n = 90).

Results: Serum VWF, sICAM-1, and sVCAM-1 levels were all elevated in asymptomatic community children with microscopy-confirmed parasitemia when compared with children without parasitemia by microscopy or polymerase chain reaction (all, P ≤ .05). Levels of VWF, sICAM-1, and sVCAM-1 were higher in children with UM than in CC (all, P < 0.001), but only VWF levels effectively distinguished CM from UM (P < 0.001), a finding confirmed by receiver operating characteristic analyses (area under the curve = 0.67; 95% confidence interval, .58-.75). Von Willebrand factor levels were lower in children with blood group O versus non-O blood groups across the disease spectrum, but VWF levels remained higher in CM versus UM, even after controlling for blood group.

Conclusions: Endothelial activation, as assessed by serum levels of VWF, sICAM-1, and sVCAM-1, occurs even in subclinical P. falciparum parasitemia. Von Willebrand factor levels increase with greater malaria disease severity. Blood group O is associated with lower VWF levels, but presence of blood group O alone does not explain the higher VWF levels seen in children with CM.

Figure 1.

Serum von Willebrand factor (VWF) levels are higher in children with cerebral malaria (CM) than uncomplicated malaria (UM) and are elevated even in children with asymptomatic parasitemia. Values are reported as a relative percent (%) of normal. Gray vertical bars indicate the median, and the bracketed numbers indicate number of samples tested. A, Serum VWF levels in children with CM, children with UM, and community children (CC). B, Serum VWF levels in asymptomatic community children, according presence or absence of Plasmodium falciparum in study participants as detected by microscopy (Smear) or polymerase chain reaction (PCR).

Figure 2.

Von Willebrand factor (VWF) levels are higher in non-O blood group children than O blood group children and decrease after 72 hours. Enzyme-linked immunosorbent assay results show the distribution of VWF levels as a percent of normal. The gray horizontal bars indicate the median, and the bracketed numbers indicate number of samples tested. Group VWF levels were compared with Wilcoxon rank sum tests, and P values are reported for the different comparisons. A, Von Willebrand factor levels in O and non-O phenotypes in community children (CC), children with uncomplicated malaria (UM), and children with cerebral malaria (CM). B, Serum VWF levels 72 hours postadmission in the children with CM, O and non-O blood groups.

Figure 3.

sICAM-1 levels do not differ and are not affected by ABO blood group in children with uncomplicated malaria (UM) and cerebral malaria (CM). A, Serum concentrations of sICAM-1 were determined for community children (CC) and children with UM or CM. B, Serum concentrations of sICAM-1 from CC were subgrouped according to the presence or absence of parasites as detected by polymerase chain reaction (PCR) and microscopy (Smear). Only CC with both PCR and microscopy results are shown. C, Serum concentrations of sICAM-1 were subgrouped by O and non-O blood group. Dot plots show the resulting distribution of values (ng/mL), with medians indicated on the plot with vertical gray bars, and the bracketed numbers indicate number of samples tested. Group levels were compared with Wilcoxon rank sum tests and P values are reported for the indicated group comparisons.

Figure 4

sVCAM-1 levels do not differ and are not affected by ABO blood group in children with uncomplicated and cerebral malaria. A, Serum concentrations of sVCAM-1 were determined for community children (CC) and children with uncomplicated malaria (UM) or cerebral malaria (CM). B, Serum concentrations of sVCAM-1 from CC were subgrouped according to the presence or absence of parasites as detected by polymerase chain reaction (PCR) and microscopy (Smear). Only CC with both PCR and microscopy results are shown. C, Serum concentrations of sVCAM-1 were subgrouped by O and non-O blood group. Dot plots show the resulting distribution of values (ng/mL), with medians indicated on the plot with vertical gray bars, and the bracketed numbers indicate number of samples tested. Group levels were compared with Wilcoxon rank sum tests and P values are reported for the indicated group comparisons.