SLU MMI -- Tom Chambers

Research Summary:
This laboratory is investigating the molecular biology and pathogenesis of flaviviruses, a family of small positive-strand RNA viruses which cause epidemic vector-borne diseases such as yellow fever, dengue fever, and Japanese encephalitis. These viruses are evolutionarily related to the pestiviruses and the hepatitis C virus, which together include a large number of agents capable of causing acute and chronic diseases of both human and veterinary/agricultural significance. Our goal is to understand at the molecular level how these viruses replicate and cause disease.

Our studies on flavivirus replication involve the genetic manipulation of a molecular clone of yellow fever virus (YF) to define functions of viral nonstructural proteins and cis-acting RNA sequences during viral replication. The goals are to understand show replication is regulated and to investigate strategies for interfering with these molecular processes. For example, a viral proteinase (consisting of a heterodimer of two viral nonstructural proteins) has been identified and shown to be necessary for proteolytic processing of the viral proteins. We are conducting genetic and structural studies of the protease to further our knowledge of molecular events occurring during replication of these viruses, and explore the development of proteinase inhibitors as antiviral agents.

Our studies on pathogenesis concern the mechanisms by which flaviviruses invade the central nervous system (CNS) and establish lethal infection within the brain. We are interested in defining the importance of both viral and host elements in this process. What constitutes the genetic determinants of viral neurovirulence is and how interaction with host cells and the host immune system influences the outcome of infection remains a fundamental question in viral pathogenesis. We are taking several approaches to these issues. Using molecular clones of YF and engineered chimeric flaviviruses designed to express combinations of virulent and nonvirulent genes from homologous and heterologous members of this family, we are defining what viral determinants are required for expression of virulent phenotypes. We are pursuing how these determinants cause biological effects by investigating the molecular biology of replication during interaction with target host cells and cells of the immune system. This involves the use of both in vitro and animal models. With the use of an animal model, our goal is to detail the nature and progression of the host immune response to the virus primarily within the central nervous system. The key questions include understanding the interaction of the virus with the resident populations of CNS cells, how these cells are influenced by infection and how the immune response operates to either contain this process or contribute to its progression. Use of a SCID (severe combined immunodeficiency) mouse system has allowed us to focus directly on CNS-specific gene expression to acute viral injury. These studies are expected to provide insight into mechanisms involved in clearing virus from sites of infection within the brain and potentially identify any viral mechanisms which counter defenses responsible for induction of an antiviral state at the cellular level. These areas of investigation will lead to a better understanding of how viruses and other pathogens enter and infect the CNS, the consequences of such infection, and how immune responses in the CNS are initiated, maintained and regulated in response to infection.