| Enterovirus 71 (EV71) is a typical positive strand RNA virus that usually causes hand, foot and mouth disease (HFMD). Acute EV71 infection may result in severe neural syndromes and even death especially among young children. To date, no effective treatment is available for EV71 infection.;Type I interferon (IFN), as the first line of host immune response, is critical in mediating viral clearance, host defense, and adaptive immunity development upon virus invasion. Recominant IFNs are also applied to treat and control several clinical viral infections. In case of EV71, previous studies showed that conventional IFNs fail to treat EV71 infection in mice. It suggests that virus has developed mechanisms to escape from type I IFN response. Uncover the underling mechanisms would help us to develop strategies to comb ate EV71 infection.;In this thesis, I firstly characterized the viral kinetics of EV71 in infected human rhabdomyosarcoma cells and analyzed the correlation between the cellular type I IFN level and viral replication. The induction of IFN-beta was observed during viral infection. However, viral replication was not restricted and quickly led to a peak post infection. These results indicated that EV71 infection sensed by host cells could activate the type I interferon production, while virus developed unkown mechanisms to antagonize the IFN response. Secondly, by analyzing with RT-PCR, the mRNA level of IFN stimulated genes (ISGs) were demonstrated to be repressed in EV71 infected cells after treated with recombinant IFN-alpha when compared with mock infected control. Thirdly, subsequent analysis showed that EV71 inhibited the type I IFN response by blocking the IFN-mediated phosphorylation of STAT1 and STAT2. Fourthly, EV71 was demonstrated to inhibit JakJSTAT signaling by promoting internalization and degradation of type I IFN receptor subunit IFNAR1. Fifthly, 2A protease encoded by EV71 was identified as an antagonist of the type I IFNs and ecotopic expression of 2Apro led to repress the expression of IFNAR1, led to inhibition of the phosphorylation of Jak1, Tyk2, STAT1 and STAT2. Finally, the site-direct mutation indicated that the protease activity of 2Apro was essential in this process, although the 2Apro could not directly cleave IFNAR1 both in vitro and in vivo.;Taken together, this study for the first time proved that EV71 was able to inhibit the cellular type I IFN response by reducing IFNAR1 level. Moreover, 2A protease encoded by EV71 was demonstrated to function as the antagonist to the IFN signaling. These data provides new knowledge of EV71 to block the host innate immune response, and may facilitate development of new antiviral therapies for EV71 or other picornaviruses infections. |
