Viral Pathogenesis and Regulation of Innate Immunity
Viruses regulate cell signaling pathways dedicated to restricting viral spread and in the process engage cellular responses that direct pathogenesis. Hantaviruses and dengue viruses infect the endothelium and nonlytically cause hemorrhagic and edematous diseases by altering fluid barrier functions of the endothelium. Endothelial cells (ECs) dynamically regulate fluid and immune cell emigration from capillaries while maintaining vascular integrity and vessel repair. In this setting failure is lethal and controlled by a series of fluid barrier failsafe mechanisms. Our lab is focused on defining mechanisms by which hantaviruses and dengue viruses regulate innate immune responses and induce pathogenesis following nonlytic infection of ECs.
Hantavirus Pathogenic Mechanisms
||Fig.1 Calcein labeled platelet binding to the surface of mock, HTNV, ANDV or TULV infected ECs, 3 days p.i.
Pathogenic hantaviruses primarily infect ECs and cause two vascular leak syndromes, hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS). Pathogenic hantaviruses alter the function of endothelial cells β3 integrins, direct the recruitment of quiescent platelets to ECs and enhance the potent permeabilizing effects of VEGF on EC monolayers. These findings are consistent with patient hypoxia and hypoxia directed VEGF induction that may contribute to the accumulation of up to 1 liter per hour of pulmonary edema fluid in HPS patients.
Hantaviruses also infect lymphatic endothelial cells (LECs) which line lymphatic vessels and regulate fluid clearance from tissues. ANDV causes the formation of giant cells resulting from the rapamycin sensitive activation of mTOR-S6K and hypoxia driven responses. Mechanisms by which hantaviruses activate mTOR and activate hypoxia directed VEGF responses in primary human ECs are being investigated in order to define potential therapeutic targets that resolve EC barrier deficits.
We have demonstrated that primary human ECs are efficiently and productively infected. However, DVs primarily infect immune cells and vascular permeability results from infection by a second DV serotype which gives rise to an immune enhanced disease process resulting in hemorrhage or edema in 1-2% of patients. Ultimately vascular permeability is the result of changes in the vascular endothelium and we have found that DV infected ECs secrete cytokines and chemokines that have the potential to contribute to immune enhanced pathogenesis. We are interested in determining the contribution of ECs to immune enhanced DV responses and the mechanism by which DV induces vascular permeability. These studies are aimed at defining viral and cellular targets for therapeutically regulating DV responses that contribute to the severity of disease in dengue patients.
Regulation of Innate Immunity
Pathogenic viruses inhibit the early induction of IFN in order to replicate within ECs and we are defining virulence determinants and mechanisms used by hantavirus N and Gn proteins and DV Nonstructural proteins to regulate TBK1 signaling responses and limit IFNb induction. Reverse genetic approaches are being developed in order to attenuate pathogenic hantaviruses.