Distinct Behaviors of Infected and Bystander Dendritic Cells Following Exposure to Dengue Virus: A Dissertation

Dengue viruses (DV) are re-emerging mosquito-borne pathogens for which four distinct lineages , grouped based on serology and referred to as serotypes 1-4 (D I V D4 V), have been described. Epidemiological data imply that re-infection with a "heterologous serotype , i. , one other than that to which the individual was originally exposed enhances the risk for development of severe disease , dengue hemorrhagic fever (DHF). The hallmark of DHF is a transient capilary leakage syndrome of rapid onset, temporally associated with the resolution of fever and viremia. In its most grave form, the vascular permeability phenomenon in DHF may progress to dengue shock syndrome (DSS), which is often fatal in the absence of appropriate medical care. Despite the fulminant natue of vascular leakage during DHF/DSS , this phenomenon does not appear to be due to direct cytopathic effects ofDV. Rather inappropriate reactivation and/or regulation of dengue-specific memory are the prevailing theorized (immunopathological) etiologies. Traditional vaccine development techniques have proven insuffcient for DV , . since any vaccine must offer complete protection against all four serotyes to avoid enhanced pathology on natural viral challenge. Understanding the underlying mechanisms that contribute to dengue disease, particularly the development of dengue-specific memory, is therefore of critical importance. Dengue immunopathology and the specific aspects of immunological memory that determine disease severity are heatedly debated. Previous research in our lab has suggested that T cell responses contribute to the severity of dengue ilness. Clinical data indicate enhanced immune activation in more grave cases of DV infection, and serotype cross-reactive T cells from multiple individuals are present after both primary and secondary dengue infections. However, little is known about the conditions under which T cells are primed and dengue-specific memory is generated. Dendritic cells (DCs) are bone' marrow-derived cells that playa central role in directing activity within the immune system. DCs shape quantitative and qualitative aspects of adaptiveimmunity, and therefore the intrinsic characteristics of host memory to a pathogen. DCs are essential in generating primary immune responses, due to their particular effectiveness in stimulating naIve T cells. DCs also play important roles in the reaCtivation of memory to an infectious agent, and as reservoirs for the dissemination of invading microorganisms. Exposure to pathogens or their products initiates a series of phenotyic and functional changes in DCs , termed maturation. DC maturation involves a coordinated response of immunomodulatory surface molecule elaboration and cytokine production, culminating in antigen presentation to, and co-stimulation of, T cells specific for the invading agent. The DC response is ostensibly tailored to facilitate effective eliniination by regulating effective downstream interactions of the DC with T cells. A number of viruses have evolved to infect DCs and alter their functional behavior, facilitating their own survival within the host, and the herd. DV readily infects DCs both in primary cell cultues and in vivo. However, reports on the effects of DV infection on DC maturation vary both with regard to some of the cytokines produced, and the phenotyes of infected versus bystander cells. Although DCs appear to be activated following DV exposure , responses on the single-cell level appear to depend on the infection state of the cell , hypothetically driven by intracellular virus-mediated effects. Therefore , downstream responses to these divergent populations, actively infected