Kinetic Analysis of Biomarkers in a Cohort of US Patients With Ebola Virus Disease

Abstract

Background: Ebola virus (EBOV) infection causes a severe and often fatal disease. Despite the fact that more than 30 000 individuals have acquired Ebola virus disease (EVD), the medical and scientific community still does not have a clear understanding of the mechanisms by which EBOV causes such severe disease.

Methods: In this study, 54 biomarkers in plasma samples serially collected from 7 patients with EVD were analyzed in an attempt to define the kinetics of inflammatory modulators. Two clinical disease groups were defined (moderate and severe) based on the need for clinical support. Biomarkers were evaluated for correlation with viremia and clinical disease in an effort to identify pathways that could be useful targets of therapeutic intervention.

Results: Patients with severe disease had higher viremia than those with moderate disease. Several biomarkers of immune activation and control were significantly elevated in patients with moderate disease. A series of pro-inflammatory cytokines and chemokines were significantly elevated in patients with severe disease.

Conclusions: Biomarkers that were associated with severe EVD were proinflammatory and indicative of endothelial or coagulation cascade dysfunction, as has been seen historically in patients with fatal outcomes. In contrast, biomarkers that were associated with moderate EVD were suggestive of a strong interferon response and control of both innate and adaptive responses. Therefore, clinical interventions that modulate the phenotype and magnitude of immune activation may be beneficial in treating EVD.

Keywords: EVD; Ebola; biomarkers; cytokines; immunity.

Figure 1.

Viremia and humoral immune responses during Ebola virus disease (EVD). Patient plasma samples were assayed by quantitative reverse-transcriptase polymerase chain reaction, and relative viremia ( A ) was determined as tissue culture infective dose 50 (TCID ₅₀ )/mL by comparison to an Ebola virus standard curve. Antinucleocapsid immunoglobulin M (IgM) ( B ) and immunoglobulin G (IgG) ( C ) titers were determined by enzyme-linked immunosorbent assay. Each patient's data are indicated by the specified color and symbol. The x -axis shows days after onset of self-reported symptoms. Of note, data for EVD2, 5, 9, and 15 have been previously reported [ 8 ].

Figure 2.

Biomarkers that were associated with moderate Ebola virus disease (EVD). Expression of each biomarker was assayed in all patient plasma samples as described. Each patient's data are indicated by the specified color and symbol. The x -axis shows days after onset of self-reported symptoms. The gray area represents the reference values of each biomarker as measured in samples from 10 healthy humans. The dotted line is the limit of the assay. For any sample that had a biomarker level that was below the limit of detection or undetectable, a non-zero value below the limit of detection was assigned to allow visualization of the data on the graph. This applies to apoptosis antigen-Fas (APO-Fas) and soluble Fas ligand (s-FasL). Abbreviations: IFN, interferon; IL, interleukin; TNFR, tumor necrosis factor receptor.

Figure 3.

Cytokines and chemokines that were associated with severe Ebola virus disease (EVD). Expression of each biomarker was assayed in all patient plasma samples as described. Each patient's data points are indicated by the specified color and symbol. The x -axis shows days after onset of self-reported symptoms. The gray area represents the reference values of each biomarker as measured in samples from 10 healthy humans. The dotted line is the limit of the assay. For any sample that had a biomarker level that was below the limit of detection or undetectable, a non-zero value below the limit of detection was assigned to allow visualization of the data on the graph. This applies to interleukin (IL)-6, IL-8, IL-10, monocyte colony stimulating factor (MCSF), and IL-1 receptor antagonist (RA). Abbreviations: MCP, monocyte chemoattractant protein; MIP, macrophage inflammatory protein; TNFR, tumor necrosis factor receptor.

Figure 4.

Other biomarkers that were associated with severe Ebola virus disease (EVD). Expression of each biomarker was assayed in all patient plasma samples as described; markers of coagulation ( A ), markers of endothelial function ( B ), and markers of T-cell activity ( C ) were examined. Each patient's data points are indicated by the specified color and symbol. The x -axis shows days after onset of self-reported symptoms. The gray area represents the reference values of each biomarker as measured in samples from 10 healthy humans. The dotted line is the limit of the assay. For any sample that had a biomarker level that was below the limit of detection or undetectable, a non-zero value below the limit of detection was assigned to allow visualization of the data on the graph. This applies to von Willebrand factor (vWF), tissue factor, and fractalkine. Abbreviations: PECAM, platelet endothelial cell adhesion molecule; sICAM, soluble intracellular adhesion molecule.