Pathogenesis and apoptosis study of infectious bursal disease virus (IBDV) and development of a bivalent recombinant IBDV vaccine

We cloned and sequenced the entire genomic segments A and B of wild-type and cell culture-adapted infectious bursal disease virus (IBDV) strain GLS. Comparison of the deduced amino acid sequences showed only two amino acid substitutions in VP2 and VP1 proteins, respectively. Reassortant viruses between attenuated strains and the wild-type virus were generated using the reverse-genetic system. The virus that contains segment B sequence from wild-type virus, rGLSBDB, replicates in cell culture but exhibits delayed replication kinetics. Moreover, wild-type virus was able to replicate only after being delivered into the cytoplasm in cell culture. In vivo, 3-week-old chickens were inoculated with equal dose of theses viruses and their bursae were harvested for pathological analysis and antigen detection. The wild-type virus propagates most efficiently and cause severe bursal lesions. The cell culture adapted and reassortant viruses do not propagate efficiently in the bursa and cause mild bursal lesions, except rGLSBDB virus, which propagates much faster and produces severe bursal lesions. Our results indicate that two amino acid residues in VP2 determine viral entry and VP1 is involved in the efficiency of viral replication and virulence in vivo.; The signal pathways and nature of IBDV induced apoptosis were investigated in order to gain more understanding of IBDV pathogenesis. IBDV-induced apoptosis occurs at the late stage of viral life cycle. Caspase 9 and 3 are activated and cytochrome c activity was detected in cytosol, indicating that the mitochondrial pathway is involved. Moreover, NF-kappaB activation is essential for IBDV induced apoptosis and reactive oxygen species (ROS) may be an upstream even of the signal pathway. The NF-kappaB inhibitor completely inhibits NF-kappaB activity and apoptosis during IBDV infection but does not affect viral replication and release. The antioxidant gives similar results on NF-kappaB activation and apoptosis but reduces viral progeny yields.; A "tailor-made", chimeric IBDV was created by use of reverse genetics approach and its vaccine potential was evaluated. The recombinant virus can induce strong humoral immune response and provide the protection against both classical and variant IBDV infection.