Infectious bursal disease virus (IBDV) causes a highly contagious disease in young chicks and leads to significant economic losses in the poultry industry. The capsid protein VP2 of IBDV plays an important role in virus binding and cell recognition. VP2 forms a subviral particle (SVP) with immunogenicity similar to that of the IBDV capsid. In the present study, we first showed that SVP could inhibit IBDV infection to an IBDV-susceptible cell line, DF-1 cells, in a dose-dependent manner. Second, the localizations of the SVP on the surface of DF-1 cells were confirmed by fluorescence microscopy, and the specific binding of the SVP to DF-1 cells occurred in a dose-dependent manner. Furthermore, the attachment of SVP to DF-1 cells was inhibited by an SVP-induced neutralizing monoclonal antibody against IBDV but not by denatured-VP2-induced polyclonal antibodies. Third, the cellular factors in DF-1 cells involved in the attachment of SVP were purified by affinity chromatography using SVP bound on the immobilized Ni 2؉ ions. A dominant factor was identified as being chicken heat shock protein 90 (Hsp90) (cHsp90) by mass spectrometry. Results of biotinylation experiments and indirect fluorescence assays indicated that cHsp90 is located on the surface of DF-1 cells. Virus overlay protein binding assays and far-Western assays also concluded that cHsp90 interacts with IBDV and SVP, respectively. Finally, both Hsp90 and anti-Hsp90 can inhibit the infection of DF-1 cells by IBDV. Taken together, for the first time, our results suggest that cHsp90 is part of the putative cellular receptor complex essential for IBDV entry into DF-1 cells.
Infectious bursal disease virus (IBDV), a member of genusAvibirnavirus of the family Birnaviridae, causes a highly contagious disease in young chicks (27). Two serotypes (serotypes 1 and 2) of IBDV have been documented. Serotype 1 showed different degrees of pathogenicity and mortality in chicks, and serotype 2 was avirulent. As with all viruses, IBDV needs to penetrate target cells to cause infection. Chicken B lymphocytes are the primary target for virulent serotype 1 strains of IBDV, and the infection causes a functional loss of the bursa of Fabricius and severe immunodepression. However, other susceptible cells have also been reported (17). Viral attachment is the first step in virus infection (41). The distribution of a virus receptor mainly determines the cell and tissue tropism of the virus (1, 11) and the site of pathology associated with infection (9, 26). Thus, study of virus infection at the levels of virus binding, receptor identification, and even uncoating is critical for an understanding of the virus-host cell interactions and pathogenesis of viral disease (24, 32). Additionally, viral entry and uncoating can serve as targets for the development of antiviral drugs (39,42). Recent advances in the understanding of the viral infection process have made it possible to develop new approaches to block the entry of viruses (31) and to prevent diseases (41). However, the identificatio...
