DEFINING DENGUE VIRUS INFECTION IN HUMAN SKIN
Abstract: The skin is the primary site of dengue virus (DENV) replication following the bite of an infected mosquito, but the factors that contribute to productive infection in human skin and virus spread out of skin are not understood. We defined the dynamics of DENV infection in human skin explants using quantitative in situ imaging. A transient IFN-α response occurred prior to the productive DENV infection, which initially established in cells in the epidermis. DENV infected a wide variety of cell types including Langerhans cells (LC), dermal macrophages (Mϕ), dermal dendritic cells (DC), fibroblasts, mast cells, and lymphatic endothelium, but keratinocytes were the earliest and quantitatively most important target of DENV infection, contributing to 60% of overall infected skin cell over time. DENV infection led to the recruitment and infection of LC, dermal DC, and dermal Mϕ. These immune cells emigrated out of the skin in increased number as a result of infection, presumably leading to dissemination of virus. Infection of keratinocytes led to the abundant production of inflammatory mediators, most significantly IL-1β. Blocking keratinocyte-derived IL-1β reduced the infection of LC, dermal DC, and dermal Mϕ by 75-90% and decreased the total number of infected cells in epidermis and dermis by 33% and 65%, respectively. In the first demonstration of antibody-dependent enhancement of DENV infection in human skin, we showed that the presence of heterotypic DENV-immune serum enhanced the recruitment and infection of dermal Mϕ by 50-70%, and increased emigration of myeloid cells out of skin. The Aedes aegypti mosquito salivary gland extract had no impact on dermal Mϕ during DENV infection, with or without immune serum. Blocking FcγRIa and FcγRIIa strongly diminished all the antibody-mediated infection of dermal Mϕ, and decreased the number of cell emigrants, resulting in the reduction of the overall number of infected cells in the dermis by 70%, without notable changes in the epidermis. Ethnic differences in skin immune responses to DENV were observed for the first time in our study. In comparison with Caucasian skin, skin from African Americans was able to maintain the protective level of antiviral IFN-α responses for at least 48 hours. This was observed in association with less DENV replication, a reduced production of IL-1β in the epidermis, less recruitment and infection of LC and dermal Mϕ, and less cell emigration out of the skin. These findings may provide a mechanism for the epidemiologic observation that African ancestry protects against severe dengue. Our findings highlight the importance of skin and the complex interplay between resident and immune skin cell populations in DENV infection and dengue pathogenesis.
Advisor: Simon Barratt-Boyes, PhD