Interaction of dengue virus with human Kupffer cells in vitro

The hepatic lesions in dengue fever consist generally of central and parace ntral focal necrosis, the presence of sinusoidal acidophilic bodies, hypert rophy of Kupffer cells in which viral antigens are occasionally found, mild fatty changes and patchy portal mononuclear cell infiltration. The role of the Kupffer cells and the nature of their interactions with dengue virus i n the course of the disease are not well known. In this study we have infec ted primary cultures of human Kupffer cells with dengue virus and examined the production of infectious particles, the synthesis of intracellular vira l antigens and the induction of the cell death by apoptosis. In a parallel study, the penetration of the virus into the cells and its cytopathic effec t have been examined by electron microscopy. Finally, we have followed the production of several cytokines and nitric oxide (NO) by infected Kupffer c ells. Our results show that viral particles are taken up by Kupffer cells mainly by phagocytosis and, less frequently, by receptor-mediated endocytosis in c lathrin-coated pits. Several pictures suggested a process of fusion. No inf ectious dengue particles were released from Kupffer cells. Viral proteins w ere synthesized in about 10% of the cells, 24 hours after infection. The pa ttern of the immunofluorescence was either speckled or concentrated in huge patches. Viral antigen-containing cells disappeared from the culture 72 ho urs after infection. Apoptotic cells could be detected by TUNEL assay and e lectron microscopy; and these were phagocytosed and degraded by neighouring Kupffer cells. Viral particles were occasionnally found associated with th e cells being degraded in phagosomes. Production of IL1-alpha, IL1-beta and IFN-gamma could not be revealed. Howe ver infected Kupffer I:ells synthetized TNF-alpha, IFN-alpha and NO as earl y as 6 hours after infection, and IL-6 after 24 hours. In conclusion, our results show that Kupffer cells are not permissive for d engue virus. In a low number of cells an abortive infection resulting in ap optotic: cell death was observed. dengue virus induces Kupffer cell activat ion, as demonstrated by IL-6, TNF-alpha, IFN-alpha and NO production. Viral particles as well as viral antigen-containing cells were rapidly taken up and degraded.