Both virus and tumor necrosis factor alpha are critical for endothelium damage in a mouse model of dengue virus-induced hemorrhage.

Hemorrhage is a common clinical manifestation in dengue patients. However, the pathogenic mechanism of dengue virus (DV)-induced hemorrhage awaits clarification. We established a mouse model of DV hemorrhage using immunocompetent C57BL/6 mice by injecting DV serotype 2 strain 16681 intradermally. While inoculation of 3 x 10(9) PFU of DV induced systemic hemorrhage in all of the mice by day 3 of infection, one out of three of those injected with 4 x 10(7) to 8 x 10(7) PFU developed hemorrhage in the subcutaneous tissues. The mice that were inoculated with 4 x 10(7) to 8 x 10(7) PFU but that did not develop hemorrhage were used as a basis for comparison to explore the pathogenic mechanism of dengue hemorrhage. The results showed that mice with severe thrombocytopenia manifested signs of vascular leakage and hemorrhage. We observed that high viral titer, macrophage infiltration, and tumor necrosis factor alpha (TNF-alpha) production in the local tissues are three important events that lead to hemorrhage. Immunofluorescence staining revealed that DV targeted both endothelial cells and macrophages. In addition, the production of high levels of TNF-alpha in tissues correlated with endothelial cell apoptosis and hemorrhage. By comparing TNF-alpha(-/-) to IgH(-/-), C5(-/-), and wild-type mice, we found that TNF-alpha was important for the development of hemorrhage. In vitro studies showed that mouse primary microvascular endothelial cells were susceptible to DV but that TNF-alpha enhanced DV-induced apoptosis. Our mouse model illustrated that intradermal inoculation of high titers of DV predisposes endothelial cells to be susceptible to TNF-alpha-induced cell death, which leads to endothelium damage and hemorrhage development. This finding highlights the contribution of the innate immune response to dengue hemorrhage.