Abstract

To test whether amino acid mutations in the PBC and PHI loops of VP2 are involved in the replication and virulence of infectious bursal disease virus (IBDV), a pair of viruses, namely the moderately virulent IBDV (rGx-F9VP2) and the attenuated strain (rGt), were used. Residue mutations A222P (PBC) and S330R (PHI), selected by sequence comparison, were introduced individually into rGx-F9VP2 by using a reverse genetics system. In addition, the reverse mutation of either P222A or R330S was introduced into rGt. The four modified viruses were then rescued and evaluated in vitro (CEF cells) and in vivo (SPF chickens). Results showed that A222P elevated the replication efficiency of rGx-F9VP2 while P222A reduced that of rGt in CEF cells. A mutation at residue 330 did not alter IBDV replication. In addition, animal experiments showed that a single mutation at either residue 222 or 330 did not significantly influence the virulence of IBDV. In conclusion, residue 222 in PBC of VP2 is involved in the replication efficiency of IBDV in vitro but does not affect its virulence in vivo, further facilitating our understanding of the gene-function of IBDV.

Highlights

  • Infectious bursal disease virus (IBDV) is the causative agent of a highly contagious disease in chickens known as infectious bursal disease (IBD)

  • In cells co-transfected with pCGxATA-G794CHRT/ pCGxBHRT or pCGxATA-T1120AHRT/pCGxBHRT, the modified infectious bursal disease virus (IBDV) rGxHT-222 or rGxHT-330 strains were rescued, which contained a single mutation A222P in PBC or S330R in PHI of VP2 compared to the virulent strain rGxF9VP2, respectively

  • In cells co-transfected with pCmGtA-C794GHRT/pCmGtBHRT or pCmGtA-A1120THRT/ pCmGtBHRT, the modified IBDV rGt-222 or rGt-330 strain was rescued, which contained the reverse mutation P222A or R330S compared to the attenuated strain rGt

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Summary

Introduction

Infectious bursal disease virus (IBDV) is the causative agent of a highly contagious disease in chickens known as infectious bursal disease (IBD). IBD causes significant losses of the poultry industry owing to its high mortality and immunosuppression in young chickens via the destruction of developing B lymphocytes in the bursa (Cosgrove, 1962; Muller et al, 2003). Segment B encodes the VP1 protein, the viral RNA-dependent RNA polymerase (Le Nouen et al, 2006; von Einem et al, 2004), while segment A contains two partially overlapping open reading frames (ORF). The smaller ORF encodes the non-structural protein VP5 (Mundt et al, 1995), while the larger one encodes a polyprotein which is cleaved into proteins pVP2, VP3, and VP4 (Birghan et al, 2000). VP2 and four peptides are further derived from the maturation of pVP2 (Da Costa et al, 2002)

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