LSUHSC COBRE: ROLE OF INNATE IMMUNITY IN YELLOW FEVER VIRUS PATHOGENESIS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Project 1: Role of Innate Immunity in Yellow Fever Virus Pathogenesis P.I.: Kate D. Ryman, Ph.D. (Reporting Period: 07/01/05 - 06/30/06) Abstract Background & Rationale: The highly-lethal, pan-systemic hemorrhagic fever caused by the mosquito-borne yellow fever virus (YFV) was one of the most feared diseases in Africa, Europe and the Americas until the live-attenuated 17D vaccine was developed in the 1930?s. To derive the 17D vaccine strain, the natural wild-type Asibi isolate of YFV was empirically passaged 176 times on primary cultured cells. Although 17D is considered a prototypic live-attenuated virus vaccine, one of the greatest mysteries in the flavivirus field is the molecular mechanism that controls the attenuation and immunogenicity of this live-attenuated vaccine. Our long-term goals are to reveal which of the mutations accumulated in the 17D genome are attenuating in vivo and determine their effect(s) on viral pathogenesis, and to determine how the attenuated infection differentially affects early virus-host interactions, eliciting a YFV-specific protective immune response after 17D immunization. The proposed experiments will differ from prior analyses in several important respects. First, we will compare the phenotype of 17D to parental Asibi to identify specific nucleotide and amino acid mutations correlated with attenuation. Second, we will assess the virulence phenotype by intradermal (i.d.) inoculation of mice, thereby mimicking the bite of a YFV-infected mosquito or 17D immunization, whereas previous studies have assessed the attenuating potential of 17D-specific mutations following intracerebral inoculation. Finally, we will focus on the earliest events in infection as the virus enters the host and begins to disseminate. It is our hypothesis that the early viremic dissemination of the live-attenuated 17D vaccine strain will be significantly impaired in comparison with the virulent parental Asibi virus as a result of a differential ability to replicate in dendritic cells (DCs), monocytes (MO) and/or macrophages (M?) in the skin and that the attenuated phenotype will correlate with induction of chemokine/cytokines appropriate for the stimulation of adaptive immunity in regional lymphoid tissues. It is anticipated that our findings will facilitate the rational design of other live-attenuated virus vaccines, particularly against other pathogenic flaviviruses (e.g., West Nile and dengue viruses) and the closely-related alphaviruses (e.g., eastern equine encephalitis virus), most of which are agents of both emerging infectious disease and bioterrorism/biowarfare.