EFFECT OF CYTOXAN(R)-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 trachea l epithelial damage of infectious bronchitis, eight 3-wk-old specific- pathogen-free chickens were made heteropenic by four daily intramuscul ar injections of cyclophosphamide at 75 mg/kg body weight. Infection w ith Massachusetts 41 infectious bronchitis virus was timed to coordina te heteropenia with peak tracheal epithelial damage. Heteropenia was m onitored by total leukocyte and differential cell counts of peripheral blood. Tissue damage and heterophil infiltrate were monitored by hist opathology of tissues taken ar termination of the study. Heteropenic b irds had lower peripheral blood and tracheal heterophil numbers than n onheteropenic birds. No difference was found in epithelial damage of h eteropenic and nonheteropenic birds. Epithelial damage in infectious b ronchitis is most likely due to damage by the virus and not due to the infiltrated heterophils.