The effects of H9N2 influenza A on the immune system of broiler chickens in the Shandong Province.

The effects of H9N2 Influenza A on T lymphocyte subsets, immune organs and the production of anti-Newcastle disease antibodies were examined after infection of broiler chickens with strain SD06 of H9N2 influenza virus. Animal models were successfully established and characterized by conventional HA and HI antigen tests. Pathological changes in the thymus, bursa of Fabricius and spleen were observed through microscopic examination. Changes in T lymphocyte subsets and lymphocyte apoptosis were detected by flow cytometry. Effects on the production of anti-Newcastle disease antibodies were examined through the β-trace method. Viruses isolated from infected chickens were confirmed to be H9N2 influenza virus. Immune organ indexes decreased significantly 7 and 14 days after broiler chickens were infected with virus. Microscopic examination showed degeneration in the thymus and bursa of Fabricius and congestive organization in the spleen. Flow cytometry results showed a significant decrease in the numbers of CD4(+) and CD8(+) T cells, as well as the CD4(+) /CD8(+) ratio, compared with controls. Annexin V-FITC/PI double-staining showed that the H9N2 virus promoted the middle and late periods in lymphocyte apoptosis. Anti-NDV antibody titres in infected chickens decreased compared with the control group. All the results showed that H9N2 virus can cause severe immune suppression and immune organ damage in broiler chickens and lead to significant reduction in the effectiveness of Newcastle disease vaccine.