Effect of Infectious Bronchitis Virus (IBV) on Lymphocyte Proliferation and T-Cell Expression of Viral Antigen in Experimentally Infected Chickens

Abstract

Background: Infectious bronchitis virus (IBV) is a major viral pathogen of poultry that causes significant economic losses worldwide. Although cell-mediated immunity is essential for controlling IBV infection, the roles of CD4⁺ and CD8⁺ T lymphocytes and viral persistence in circulating lymphocytes remain incompletely understood. Objective: To investigate changes in circulating CD4⁺ and CD8⁺ T-lymphocyte populations, detect IBV antigen in peripheral blood mononuclear cells (PBMCs), and evaluate the effect of Cyclosporine A (CSA)-induced immunosuppression on viral persistence. Materials and Methods: Seventy-five specific pathogen-free chicks were divided into infected (n = 50) and control (n = 25) groups. PBMCs were collected at different time points after IBV infection and CSA treatment. Flow cytometry was used to quantify CD4⁺, CD8⁺, and IBV antigen-positive cells. An in vitro lymphocyte infection assay was performed, and viral replication was confirmed by embryonated egg inoculation and RT-PCR. Results: IBV antigen was detected in circulating PBMCs during acute infection, with peak expression on day 7 post-infection (P < 0.005). CD4⁺ T lymphocytes increased significantly on days 14 and 21, whereas CD8⁺ T lymphocytes increased markedly from day 10 onward, indicating their important role in viral clearance. CSA treatment significantly reduced both CD4⁺ and CD8⁺ T-cell populations and resulted in more than 60% of lymphocytes expressing IBV antigen, suggesting viral persistence or reactivation. IBV also replicated successfully in isolated lymphocytes in vitro. Conclusion: CD8⁺ T lymphocytes are critical for controlling acute IBV infection, while CD4⁺ T cells support adaptive immune responses. Immunosuppression enhances viral persistence, and lymphocytes may serve as a reservoir for IBV. These findings provide valuable insights for improving IBV vaccination and disease-control strategies.

Keywords: Infectious bronchitis virus; CD4⁺ T lymphocytes; CD8⁺ T lymphocytes; Cyclosporine A; Flow cytometry; PBMCs; Viral persistence; Chickens.