A. Schroder et al., VP5 and the N terminus of VP2 are not responsible for the different pathotype of serotype I and II infectious bursal disease virus, J GEN VIROL, 82, 2001, pp. 159-169
Two serotypes have been identified in infectious bursal disease virus (IBDV
), a member of the family Birnaviridae. A reverse genetics system was used
for generation of chimeras in genome segment A of the two serotypes, in whi
ch the complete viral VP5 gene and 3' noncoding region (NCR), or parts ther
eof, were exchanged. The engineered viruses were characterized in vitro and
in vivo in comparison to serotype I and II IBDV. Our results show that IBD
V chimeras exhibit a different phenotype in cell culture compared to the wi
ld-type viruses. In in vitro-cultivated bursal-derived cells, chimeric viru
ses infected B lymphocytes, as does serotype I IBDV, Surprisingly, serotype
II virus was also able to infect in vitro-cultivated bursal cells, but the
se were neither B lymphocytes nor macrophages. After infection of susceptib
le chickens all chimeras replicated in the bursa of Fabricius (BF), and thr
ee chimeric viruses caused mild depletion of bursal cells. In contrast, aft
er infection of chickens with a chimeric IBDV containing exchanged VP5 as w
ell as 3'-NCR, no depletion was detectable. The serotype II strain did not
replicate in the BF nor did it cause depletion of bursal cells. Thus, the o
rigin of VP5 does not explain the different pathotype of IBDV serotype I an
d II.