Effect of cytoxan-induced heteropenia on the response of specific-pathogen-free chickens to infectious bronchitis

Epithelial damage in infectious bronchitis occurs early in the disease process. Heterophil infiltration into the tracheal mucosa is greatest at that time. To determine the contribution of heterophils to tracheal epithelial damage of infectious bronchitis, eight 3-wk-old specific-pathogen-free chickens were made heteropenic by four daily intramuscular injections of cyclophosphamide at 75 mg/kg body weight. Infection with Massachusetts 41 infectious bronchitis virus was timed to coordinate heteropenia with peak tracheal epithelial damage. Heteropenia was monitored by total leukocyte and differential cell counts of peripheral blood. Tissue damage and heterophil infiltrate were monitored by histopathology of tissues taken at termination of the study. Heteropenic birds had lower peripheral blood and tracheal heterophil numbers than nonheteropenic birds. No difference was found in epithelial damage of heteropenic and nonheteropenic birds. Epithelial damage in infectious bronchitis is most likely due to damage by the virus and not due to the infiltrated heterophils.