The VP5 protein of infectious bursal disease virus promotes virion release from infected cells and is not involved in cell death

The VP5 protein of infectious bursal disease virus (IBDV) was shown in previous reports to be involved in the cytopathogenicity of IBDV. Here, using a rescued VP5-deficient IBDV infectious clone, it was demonstrated that a lack of VP5 expression significantly hinders the release of viral progeny from infected cells but does not block intracellular virus production. Monoclonal VP5-expressing Vero cells did not exhibit induction of cell death. Using VP5-specific mAbs generated in our laboratory as a tool, it was shown by flow cytometry analysis that VP5 was detectable on the surface of IBDV-infected and monoclonal VP5-expressing Vero cells and bursal cells in IBDV-infected chickens. Taken together, these data suggest that the VP5 protein is involved in regulation of the release of intracellular IBDV virions and may be used as a cell-surface marker for detecting IBDV-infected cells in FCM analysis. This study contributes to the further characterization of the VP5 protein, which will allow a better understanding of the mechanism of IBDV pathogenicity.