S1 of distinct IBV population expressed from recombinant adenovirus confers protection against challenge

Protective properties of three distinct infectious bronchitis virus (IBV) Ark Delmarva poultry industry (ArkDPI) S1 proteins encoded from replication-defective recombinant adenovirus vectors were investigated. Using a suboptimal dose of each recombinant virus, we demonstrated that IBV S1 amino acid sequences showing > or = 95.8% amino acid identity to the S1 of the challenge strain differed in their ability at conferring protection. Indeed, the S1 sequence of the IBV population previously designated C4 (AdIBVS1.C4), which protected the most poorly, differs from the S1 sequence of population C2 (AdIBVS1.C2), which provided the highest protection, only at amino acid position 56. The fact that a change in one amino acid in this region significantly altered the induction of a protective immune response against this protein provides evidence that the first portion of S1 displays relevant immunoprotective epitopes. Use of an optimal dose of AdIBVS1.C2 effectively protected chickens from clinical signs and significantly reduced viral load after IBV Ark virulent challenge. Moreover, increased numbers of both IgA and IgG IBV-specific antibody secreting lymphocytes were detected in the spleen after challenge. The increased response detected for both IgA and IgG lymphocytes after challenge might be explained by vaccine-induced B memory cells. The fact that a single vaccination with Ad/IBVS1.C2 provides protection against IBV challenge is promising, because Ad-vectored vaccines can be mass delivered by in ovo inoculation using automated in ovo injectors.