Antibody Responses to Variant Surface Antigens and Biomarkers of Endothelial Damage and Repair in The Development of Cerebral Malaria

ABSTRACT

Background:

The pathogenesis of cerebral malaria (CM) is still recognized as multifaceted, despite the plausible explanation provided by the high degree of sequestration of parasitized erythrocytes in major organs of the body. Postmortem studies have demonstrated the presence of hemorrhage, deposition of fibrin and clots in blood vessels of the body where sequestration has been observed. These findings support a potential association between sequestration, endothelial damage and repair, in the development of cerebral malaria. Considering the evidence, it is plausible that associated biomarkers of these pathogenetic features may be related in the development of CM. The aim of this study was to determine the association between the development of CM and the levels of circulating endothelial cells (CECs), endothelial progenitor cells (EPCs) and antibody responses to variant surface antigens (VSA). Materials and methods: Seventy two children including nineteen CM patients, fifteen severe malaria anemia (SMA) patients, ten uncomplicated malaria (UM) patients and twenty eight healthy controls (HC) were recruited from hospitals within Greater Accra region. Whole blood sample obtained with consent from the patients was separated into plasma and erythrocytes. Five parasite isolates including three obtained from CM patients and one each from an UM and a SMA patient were successfully cultured and the erythrocytes expressing VSAs were separated. Plasma from the seventy two patients was then tested against VSAs expressed by each parasite isolate and the levels of plasma anti-VSA antibody responses were determined using flow cytometry. Additionally, levels of CECs and EPCs were determined from whole blood using flow cytometry. xiv Results: For the CM parasite isolates tested, there were significant differences in the levels of anti-VSACM antibody responses between the groups (ANOVA: CM1, p = 0.048; CM2, p = 0.006; CM3, p = 0.042). Post hoc analysis revealed that, levels of antibody responses to CM3 isolate were higher in the CM group than the HC. Conversely, levels of antibody responses to CM2 were higher in the SMA group than the HC group. For CM1 isolate, there were no differences in the antibody levels between the groups. For the non-CM parasite isolates, the levels of antibody responses were different between the groups (ANOVA: VSAUM, p = 0.008; VSASMA, p < 0.0001).

Levels were higher in the CM group than the other study groups following post hoc analysis. Taken the above results together, the levels of antibody responses were higher in the CM group than the other groups suggesting that CM may have induced the production of cross reactive antibodies with broad spectrum of recognition. For CECs, there were no significant differences in the levels between the study groups. (ANOVA, p = 0.088). However, levels of EPCs were lower in the CM group compared to the UM group (ANOVA, p < 0.05). Logistic regression analysis revealed that a unit increase in the levels of EPCs decreases the odds of a UM patient developing CM by 0.09 when the levels of CECs and anti-VSAs were held constant. Conversely, there was no association between the development of CM and the levels of CECs and anti-VSA antibody responses when the effects of the other biomarkers were held constant. Conclusion: There was a negative association between the levels of EPCs and the development cerebral malaria. Despite the results, it may be premature to make conclusions regarding the potential associations between development of CM and these biomarkers evaluated merely based on this study. This is particularly true when one considers the potential effects of small sample sizes and potential confounding variables that were not measured in this study.