Immune Status Assessment by Abundance of IFN-αand IFN-γmRNA in Chicken Blood

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Abstract
Avian diseases, including such viral infection as infectious bursal disease, infectious anemia, and Marek's disease, often cause immunosuppression, leading to more severe infection, problems with secondary infection, and inadequate responses to vaccination. Immunosuppression thus causes serious economic losses in commercial poultry production. To date, methods for assessing immune status have been too slow to be of practical help. Reasoning that immunosuppression should be reflected by reduced production of interferons (IFN) in response to a viral antigen, we have developed competitive nucleic acid hybridization microtiter plate assays for chicken IFN-α (ChIFN-α) and ChIFN-γ mRNA. To evaluate the assay, chickens were challenged with inactivated Newcastle disease virus (iNDV). Whole blood samples were collected at various times subsequently and preserved with a cationic detergent. Later, total RNA was extracted, and mRNA for both ChIFN-α and ChIFN-γ was measured. Both rose from undetectable levels to reach a peak by 4 h, remained high for about 3 days, and fell to undetectable levels by day 5. Results were similar in chickens aged between 1 and 28 days. In later experiments, blood was collected 4 h after viral challenge. When chickens were immunosuppressed by administering 4-5 mg cyclophosphamide (CY) daily for 3 days and challenged with iNDV, they transcribed less ChIFN-α and ChIFN-γ mRNA, and their antibody response was impaired. Our results suggest that suspected immunosuppression in a commercial flock could be assessed within 2-3 days by challenging birds with iNDV and measuring the amounts of ChIFN-α and ChIFN-γ mRNA in blood obtained 2-4 h later.