Immunogenicity of HA-expressing baculoviruses. (A,) ELISA antibody levels in chicken induced by various immunogens via intramuscular infection. (B) ELISA antibody levels induced by various immunogens via intranasal inoculation. Each group (n = 5) of chickens were immunized with different vaccines at the same dose of virus particles or protein contents. Two weeks after the second vaccination, serum samples from individual chickens in each group were tested by ELISA with purified virion of H5N1 (VNH5N1-PR8/CDC-RG) as antigen. The results are expressed as the absorbance of 1:100 diluted individual sera at OD490. (C) Immunohistochemistry with frozen tissue sections from vaccinated chickens. Thymus was collected from intramuscularly immunized chickens and lung was collected from intranasally immunized chickens. PBS: tissues from control chickens with PBS.