Original article from: LiveScience posted on October 20, 2015. by Ashley P.
Elke Mühlberger, PhD
Associate Professor, Microbiology
Associate Director, Biomolecular Production Core
Diploma in Biology, Philipps University, Marburg, Germany
PhD, Philipps University, Marburg, Germany
Ebola (EBOV) and Marburg virus (MARV), the only members of the filovirus family, are causative agents of viral hemorrhagic fever. With mortality rates as high as 90%, these viruses represent some of the most deadly human pathogens. We are interested in identifying virus- and cell-specific factors that contribute to virulence and pathogenicity of these viruses. A hallmark of filovirus infection is the massive impairment of the host immune response. Infected individuals who go on to succumb to EBOV infection exhibit dysregulated immune responses which appears to result from several factors, including viral mediated impairment and dysregulation of innate immune responses and subsequent failure to develop protective adaptive immunity. Studies of both human survivors and in animal models of EBOV disease suggest that a well-regulated cytokine response early in the course of the infection may be crucial to the outcome of the disease. We are interested in the characterization of the earliest events that occur in the interaction of the virus with cells of the host immune systems. The important early events are likely to center around monocytes, macrophages, and dendritic cells. These cells not only orchestrate innate and adaptive immune responses but are also the initial targets of viral infection. However, the available data on how these cells respond to EBOV infection is fragmentary and often contradictory. Therefore, developing a conceptual framework to understand how EBOV affects early innate responses remains challenging. The main objectives of this project are to: identify key events that lead to dysregulated immunity in fatal EBOV disease, identify correlates of protection in survivors of EBOV infection and identify potential targets for therapeutic intervention both early in the host innate immune response, and later when uncontrolled inflammatory responses ensue. Currently, the laboratory is characterizing the profiles of early cytokine and chemokine expression in EBOV infection to compare how they differ to highly pathogenic less pathogenic EBOV. We are also interested in the role of Toll-like receptors (TLRs) during EBOV infection.
As many other viruses, filoviruses have evolved mechanisms to evade the type I interferon (IFN) system. Both MARV and EBOV counteract not only IFN induction but also IFN signaling. We could show that MARV inhibits IFN signaling by a mechanism different from that employed by EBOV. Moreover, Marburg and Ebola viruses use different proteins to block IFN signaling pathways. These observations identify an important difference in the biology of MARV and EBOVs. Current studies are focused on investigating the molecular mechanism of MARV-mediated IFN antagonism.
With regard to the virus-specific determinants, we are mainly interested in the filovirus replication machinery. Filoviruses belong to the group of nonsegmented negative-sense RNA viruses. The viral genome is replicated and transcribed by the virus-encoded RNA-dependent RNA polymerase complex. Our working hypothesis is based on the idea that high replication efficiency may be a prerequisite for high virulence. According to this hypothesis, viral infection should be controlled by the infected host if the replication efficiency is reduced. In order to compare the replication and transcription efficiency of filovirus species that differ in their pathogenicity, we have established minigenome systems for the highly pathogenic EBOV species Zaire, the less pathogenic EBOV species Reston and MARV. These systems are used for detailed investigation of cis-acting signals on the RNA genome and for structure-function analyses of the viral proteins involved in replication and transcription. Minigenome systems are useful tools to investigate the filoviral replication cycle under low biosafety level conditions.
Together, these investigations will provide a better understanding of how filoviruses evade or modulate cellular antiviral mechanisms and will help to develop antiviral countermeasures.
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