The Influence Of Host Protein TvbS3 On The Replication Of Infectious Bursal Disease Virus

Infectious bursal disease virus(IBDV) is the causative agent of Infectious bursal disease(IBD), which is an acute, highly contagious and lethal infectious disease of young chickens. IBDV mainly targets the central immune organs-bursa of fabricius in a very complex and comprehensive manner by destroying B lymphocytes. Recovery from disease or subclinical infection will be followed by immunosuppression, which may affect the immune response of chickens to subsequent vaccinations, and thus causing serious damage to the development of poultry industry.IBDV is a typical member of the genus Avibirnavirus belonging to the Birnaviridae family. The viral genome consists of two segments of double-stranded RNA(A and B), which are approximately 3200 and 2800 nucleotides(nt) long, respectively, encoding 5 proteins. VP2 is the major structural protein and the only component of viral capsid, which is considered to be the major host-protective antigen and is responsible for the viral virulence and cell-tropism. The binding between virus and viral receptor is the first step of viral infection. Although several proteins have been predicted to be involved in the process of IBDV infection, the real viral cell protein and its pathogenic mechanism is still not clear.In this study, we extracted the membrane proteins of chicken B lymphocyte. Then we used monoclonal antibody of VP2 to screen host proteins interacting with IBDV by Co-immunoprecipitation(Co-IP) coupled with Mass spectrometry(MS). The result of MS indicated that host protein TvbS3 may have interaction with IBDV. Then real-time RT-PCR was performed to detected TvbS3 expression in B cells infected with IBDV Gx strain and DF1 cells infected with IBDV Gt Strain. The results indicated that TvbS3 expression in mRNA level was upregulated in IBDV infected cells. Previous studies have predicted that TvbS3 is cellular receptor for the cytopathic subgroups B and D of avian leucosis virus(ALV-B and ALV-D). TvbS3 is a member of Tumor Necrosis Factor Receptor(TNFR) super family, belonging to the type I transmembrane protein. The predicted cytoplasmic tail of TvbS3 contains a death domain, which can be activated by binding to ligands or receptor-specific antibodies and then induce apoptosis.In order to confirm whether TvbS3 plays an important role during IBDV infection, we cloned chicken TvbS3 gene and then further studied the influence of TvbS3 on the replication of IBDV. The results showed that over-expression of TvbS3 promoted IBDV replication, whereas down-regulation of TvbS3 by small interfering RNAs(siRNA) suppressed the replication of IBDV, which indicated that TvbS3 is a beneficial factor during IBDV infection. Recombinant chicken TvbS3 was then expressed to detect the mechanism of its influence on IBDV replication. The results of IBDV binding inhibition assay revealed that soluble TvbS3 significantly inhibited the binding efficiency of IBDV to susceptible cells in some degree.In this study, we identified a novel host cell membrane protein TvbS3 plays an important role during IBDV infection. It can promote the proliferation of IBDV in susceptible cells. Taken together, TvbS3 is probably one of the important components of IBDV putative cellular receptor complex. This study has significant meanings to further understand the pathogenic mechanism of IBDV.