Ebola virus glycoprotein directly triggers T lymphocyte death despite of the lack of infection

PLoS Pathog. 2017 May 22;13(5):e1006397. doi: 10.1371/journal.ppat.1006397. eCollection 2017 May.

Abstract

Fatal outcomes of Ebola virus (EBOV) infections are typically preceded by a 'sepsis-like' syndrome and lymphopenia despite T cells being resistant to Ebola infection. The mechanisms that lead to T lymphocytes death remain largely unknown; however, the degree of lymphopenia is highly correlative with fatalities. Here we investigated whether the addition of EBOV or its envelope glycoprotein (GP) to isolated primary human CD4+ T cells induced cell death. We observed a significant decrease in cell viability in a GP-dependent manner, which is suggestive of a direct role of GP in T cell death. Using immunoprecipitation assays and flow cytometry, we demonstrate that EBOV directly binds to CD4+ T cells through interaction of GP with TLR4. Transcriptome analysis revealed that the addition of EBOV to CD4+ T cells results in the significant upregulation of pathways associated with interferon signaling, pattern recognition receptors and intracellular activation of NFκB signaling pathway. Both transcriptome analysis and specific inhibitors allowed identification of apoptosis and necrosis as mechanisms associated with the observed T cell death following exposure to EBOV. The addition of the TLR4 inhibitor CLI-095 significantly reduced CD4+ T cell death induced by GP. EBOV stimulation of primary CD4+ T cells resulted in a significant increase in secreted TNFα; inhibition of TNFα-mediated signaling events significantly reduced T cell death while inhibitors of both necrosis and apoptosis similarly reduced EBOV-induced T cell death. Lastly, we show that stimulation with EBOV or GP augments monocyte maturation as determined by an overall increase in expression levels of markers of differentiation. Subsequently, the increased rates of cellular differentiation resulted in higher rates of infection further contributing to T cell death. These results demonstrate that GP directly subverts the host's immune response by increasing the susceptibility of monocytes to EBOV infection and triggering lymphopenia through direct and indirect mechanisms.

MeSH terms

  • CD4-Positive T-Lymphocytes / cytology*
  • CD4-Positive T-Lymphocytes / metabolism
  • CD4-Positive T-Lymphocytes / virology
  • Cell Death
  • Cells, Cultured
  • Ebolavirus / genetics
  • Ebolavirus / metabolism*
  • Hemorrhagic Fever, Ebola / genetics
  • Hemorrhagic Fever, Ebola / metabolism
  • Hemorrhagic Fever, Ebola / physiopathology*
  • Hemorrhagic Fever, Ebola / virology
  • Host-Pathogen Interactions
  • Humans
  • Protein Binding
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism
  • Viral Envelope Proteins / genetics
  • Viral Envelope Proteins / metabolism*

Substances

  • TLR4 protein, human
  • Toll-Like Receptor 4
  • Viral Envelope Proteins
  • envelope glycoprotein, Ebola virus

Grant support

National Institutes of Health grant U19 AI109945-01 Project 2 Molecular Basis for Ebola Virus Immune Paralysis (AB). National Institutes of Health grant 1R01AI102887-01A1 (AB). National Institutes of Health, the Office of the Director grant P51OD010425 (MGK). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.