Summary auto-generated
This study evaluated a recombinant baculovirus expressing the S1 glycoprotein of infectious bronchitis virus (IBV), a pathogenic coronavirus of poultry, as a vaccine candidate. The S1 gene from the virulent nephropathogenic KM91 strain was cloned and expressed in insect cells using a baculovirus expression system. Protection was assessed by challenging vaccinated chickens with virulent virus and measuring viral recovery from kidneys and tracheas. Three immunizations with recombinant S1 glycoprotein provided 50% kidney protection in unprimed chickens, compared to 88% for inactivated whole virus. In chickens pre-immunized with attenuated H120 vaccine, recombinant S1 induced 83% kidney protection after two booster doses. The recombinant glycoprotein also stimulated haemagglutination-inhibition antibodies, particularly after multiple immunizations and viral challenge. However, antibody titers did not directly correlate with protection, suggesting cell-mediated immunity may be important. While the baculovirus-expressed S1 protein was less protective than inactivated whole virus, these results demonstrated that the S1 glycoprotein alone can induce protective immune responses against IBV infection.
Key findings
- Recombinant baculovirus-expressed S1 glycoprotein induced 50% kidney protection after three immunizations in naive chickens, compared to 88% for inactivated whole virus.
- Pre-immunization with heterologous attenuated H120 vaccine enhanced protection; recombinant S1 then achieved 83% kidney protection with two booster doses.
- The recombinant S1 glycoprotein stimulated haemagglutination-inhibition antibodies but antibody titers did not correlate with protective immunity, indicating cell-mediated immunity may play a role.
- Multiple immunizations were necessary for significant protection with the recombinant antigen, suggesting dose and frequency optimization may improve vaccine efficacy.
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Abstract
A recombinant baculovirus containing the S1 glycoprotein gene of the virulent nephropathogenic KM91 strain of infectious bronchitis virus (IBV) was constructed in order to investigate protective immunity in vaccinated chickens. Results from the protection test were evaluated by re-isolation of virus from the kidneys and tracheas of vaccinated chickens after challenge with strain KM91. After three immunizations, the recombinant S1 (rS1) glycoprotein induced 50% protection of the kidney, whilst inactivated KM91 induced 88% and 50% protection of the kidney and trachea, respectively. In chickens primed with the attenuated H120 vaccine strain, which is heterologous to KM91, the rS1 glycoprotein induced 83% protection of the kidney after two immunizations. Haemagglutination-inhibition titres were also increased in chickens immunized with the rS1 glycoprotein after three immunizations, and significantly higher titres were detected after challenge. These data indicate that the expressed rS1 glycoprotein alone can induce a protective immune response as well as an antibody response.