Tembusu Virus Mainly Infection Of Monocytes/macrophages By Extensive Subversion Of Host Antiviral Innate Immune Responses

Tembusu virus is a newly emerging infectious pathogenic flavivirus causing avian disease in China,the epidemiological features of which contain an expanding host range,cross-species transmission and rapid spreading through both insect-borne and air-borne channels.TMUV is the only flavivirus found to cause disease in ducks.After infection,TMUV mainly invades the reproductive system and causes a sharp decline in egg production in affected female ducks.The data indicated that TMUV infection poses a big threat to the poultry industry in China.The immune cells have been shown to be important targets for many flavivirus,including Dengue virus and Zika virus.However,the interactions between TMUV and host immune cells remain largely unclear.In present study,the tropism of TMUV infection was detected in vivo and in vitro in the different cell subpopulations of peripheral blood mononuclear cells(PBMC)purified by differential adhesion and/or flow cytometry sorting.We found that TMUV had a significant preference to MPS during the infection of PBMC.The infection of MPS was crucial for viral replication,transmission and pathogenesis,since viral loads in ovary and spleen,viral shedding through fecal-oral route,and pathogenic damage to the ovary were all reduced by the depletion of MPS by Clodronate lipsomes.The mononuclear phagocytic system(MPS)is a major component of the body's immune system,which mainly consists of monocytes in the blood and macrophages in tissues.These cells have strong non-specific phagocytic ability and are the first line of host immune to fight against pathogens.To further explore the molecular mechanisms of TMUV infection of macrophages,the responses of macrophages to TMUV infection were investigated by genome-wide transcriptional profile analysis(RNA-seq)using chicken macrophage cell line HD11 infected with TMUV as the research model.TMUV infection altered the transcriptional profiles of HD11 cells significantly.The up-regulated differentially expressed genes(DEGs)were mainly enriched in the type I interferon related signaling pathway(IFN-?),while the down-regulated DEGs were mainly gathered in the cellular oxidation-related pathways.Despite the activation of major pattern-recognition receptor signaling,the inductions of IFN-? and IFN-? were blocked by TMUV infection on transcription and translation levels respectively.Further studies demonstrate that TMUV infection blocks IFN-? translation most likely at translation elongation stage,instead of translation initiation stage,and promote the process of protein degradation,with little effect on IFN-? secretion.Despite of the repression of type I IFNs,some chicken interferon stimulated genes(ChISGs)were still induced by TMUV infection,indicating the existence of a type I IFN-independent mechanisms in chicken macrophages upon TMUV infection.Meanwhile,TMUV maintains intracellular redox homeostasis in host macrophages,which is essential for TMUV infection,since TMUV infection could be suppressed significantly by pre-promotion of Reactive oxygen species(ROS)using phorbol-12-myristate-13-acetate(PMA).Further studies found that TMUV infection not only inhibited the expression of NADPH oxidase-related genes,but also promoted the nuclear entry of transcription factor Nrf2 to activate the expression of antioxidant genes such as SOD-1.Besides,TMUV facilitated Salmonella pullorum(S.pullorum)co-infection of macrophages,implicating that the extensive subversion of host antiviral innate immune responses by TMUV infection in macrophage we revealed might contribute to the high incidence of co-infection in TMUV-infected flocks.Collectively,present study identify an essential step of TMUV infection and reveal extensive subversion of host antiviral innate immune responses,possibly helping to extend our understanding of flaviviruses infection in birds and lay a foundation for further illustration of the molecular mechanisms underlying TMUV infection and immunity.