Infectious Bronchitis Virus Immune Responses in the Harderian Gland upon Initial Vaccination

Area of Science:

• Poultry immunology
• Vaccinology
• Avian virology

Background:

• Infectious bronchitis virus (IBV) vaccination is crucial for poultry health.
• Arkansas Delmarva Poultry Industry (ArkDPI)-derived vaccines show heterogeneity, leading to ambiguous cell-mediated immune response data.
• The Harderian gland (HG) is a key site for ocular and respiratory immune responses in chickens.

Purpose of the Study:

• To investigate the impact of Massachusetts (Mass)-type IBV vaccine administration timing (day 1 vs. day 7) on Harderian gland immune responses in chickens.
• To compare cell-mediated immunity in the HG following vaccination with a stable Mass-type IBV vaccine versus heterogeneous ArkDPI-derived vaccines.
• To determine if delaying vaccination optimizes immune responses against IBV.

Main Methods:

• Chickens were vaccinated with a Mass-type IBV vaccine on day 1 or day 7 of age.
• Serum antibody levels and lachrymal IgA were measured.
• Cellular immune responses, including B cells, T-helper (CD3+CD4+) cells, and cytotoxic T (CD3+CD8+) cells, were analyzed in the Harderian gland.

Main Results:

• Vaccination on day 7 resulted in significantly higher IBV serum antibodies and lachrymal IgA compared to vaccination on day 1.
• A clear trend of increased B cells and T-helper (CD3+CD4+) cells was observed in the HG of chickens vaccinated on day 7.
• Cytotoxic T cells (CD3+CD8+) also showed an increase in the HG following day 7 vaccination compared to day 1 vaccination.

Conclusions:

• Vaccination timing significantly impacts both humoral and cell-mediated immune responses in the chicken Harderian gland.
• Using a stable Mass-type IBV vaccine allows for clearer characterization of immune responses compared to heterogeneous vaccines.
• Postponing the initial IBV vaccination to day 7 of age may enhance protective immunity, especially in regions with a higher likelihood of early IB outbreaks.