Cell-mediated immunity after ocular Ark-type infectious bronchitis virus vaccination

Abstract

Infectious bronchitis (IB) virus (IBV) is an endemic pathogen of poultry industry causing considerable economic losses by reducing quality and quantity of egg and meat production in chickens. In spite of intensive vaccination programs, outbreaks of IB occur and are difficult to control due to serotypic heterogeneity among IB viruses. Although antibodies are important for controlling IBV, accumulating evidence indicates that cytotoxic T cell responses are very important in the initial phase of an immune response to IBV. To better understand the cell-mediated immune responses induced by IBV vaccination, we evaluated IBV-specific immune responses in mucosal and systemic immune compartments after vaccination with an Arkansas (Ark) type vaccine. Chickens were ocularly immunized with 3x105 or 3x104 50% embryo infectious doses of the Ark-type IBV vaccine at 3 and 7 weeks of age. Lymphocyte counts in conjunctiva-associated lymphoid tissues (CALT), harderian glands (HG) and spleen showed that IBV-specific immune response in secondary lymphoid tissues followed the pattern of a lag, expansion, and contraction phase as has been reported for mammals. The proportion of CD3+CD44+ T cells in the spleen, HG and CALT, as measured by flow cytometry, showed a significant (p value <0.05) increase between 9-11 days after vaccination. In the primary response to IBV vaccination, interferon-gamma (IFN-γ), granzyme A (GZMA) and perforin mRNA expression in CALT and HG displayed significant increases, whereas no significant response was observed in the spleen. After boosting, the IFN-γ mRNA expression was predominant in the spleen and to some extent in the HG, while a significant increase in GZMA mRNA expression was only observed in the CALT. Hence, the IFN-γ and cytotoxic response to IBV occurs predominantly in the mucosal immune compartment during the primary response, while the secondary IFN-γ response shifts to the systemic immune compartment. Thus, Ark-type IBV vaccination induces a central memory IFN-γ response while the cytotoxic effector memory response as measured by GZMA and perforin mRNA expression, remains associated with CALT. Studies conducted in our laboratory showed that IgA antibody responses to IBV vaccination occurred predominantly in HG. Together, these data indicate that the mucosal-associated lymphoid tissues in chickens may each serve a different function in virus-specific immunity.