Tissue culture infectivity of different strains of infectious bursal disease virus is determined by distinct amino acids in VP2

Two types of strains of serotype I of infectious bursal disease virus (IBDV ) have been described, on the basis of their ability (IBDV-TC) or inability (IBDV-BU) to infect chicken embryonic cells in culture. However, both type s infect B lymphocytes in the bursa of Fabricius of young chickens. To dete rmine the molecular basis for tissue culture infectivity, virus recombinant s with chimeric segments A were constructed from IBDV-TC and IBDV-BU by rev erse genetics. The region responsible for the different phenotypes was loca ted in VP2. Site-directed mutagenesis identified single amino acids that ar e responsible for the restriction in infectivity. However, the appropriate amino acid exchanges are strain-specific.