Human TLR3 recognizes dengue virus and modulates viral replication in vitro

The elicitation of large amount inflammatory cytokine in serum has been developed as the cause of the plasma leakage in dengue fever (DF)/dengue haemorrhagic fever (DHF) infection. Virus recognition in innate immunity is the key. The Toll-like receptors (TLRs) play an important role in pathogen recognition towards cytokine induction among several viruses; however, the role of TLRs on innate immune recognition against DENV remains unclear. This study aims at the interaction between dengue virus (DENV) and human TLRs at the incipient stage of infection in vitro. Our experiment reveals that stably expression of TLR3, 7, 8 on HEK293 enables IL-8 secretion after DENV recognition. By the model of human monocytic cells U937, we demonstrated the trigger of IL-8 after viral recognition of human monocytic cell is primary through TLR3 following endosomal acidification. Silencing of TLR3 in U937 cells significantly blocks the DENV-induced IL-8 production. Besides, the interaction is further corroborated by colocalization of TLR3 and DENV RNA upon DENV internalization. Furthermore, in this study we found the expression of TLR3 can mediate strong IFN-α/β release and inhibit DENV viral replication significantly, thus limit the cytopathic effect. ? 2009 Blackwell Publishing Ltd.