Pathogenesis of infectious bronchitis: Role of the respiratory tract cellular response

Richard Michael Fulton, Purdue University

Abstract

Cells within the respiratory tract of non-infected, specific-pathogen-free (SPF) chickens were recovered by lavage. Epithelial cells were the most prevalent and second most prevalent cells recovered from 2- and 6-week-old SPF chickens, respectively. Heterophils were the second most prevalent and most prevalent cells recovered by lavage from 2- and 6-week-old SPF chickens, respectively. In descending order of prevalence, the remainder of recovered cells from both age groups were lymphocytes, macrophages, eosinophils and basophils. When compared to mammals, chickens have smaller numbers of lavage recovered cells. The predominant phagocytic lavage cell of chickens is the heterophil, while that of mammals is the macrophage. Chickens were infected with Massachusetts 41 (MASS) infectious bronchitis virus (IBV) and cells were recovered by lavage at 2, 8, 24, 48, 72 and 96 hours post-infection (PI). This experiment was repeated with a nephropathogenic IBV, Australian T (AUS). Birds infected with MASS had more recovered cells than AUS or non-infected chickens. Total cells recovered, most of which were heterophils, from MASS chickens increased from 24 to 96 hours PI. Heterophils paralleled total cells and peaked at 72 hours PI. Lymphocytes increased from 72 to 96 hours PI. Macrophages increased from 48 to 96 hours PI. In AUS chickens, total lavage cells did not exceed non-infected chickens. Only lymphocytes exceeded those of non-infected chickens. Epithelial damage, monitored by histopathology, occurred consistently in the trachea and was greatest in MASS chickens. Peak epithelial damage occurred during lamina proprial heterophil infiltration and coincided with increasing lavage heterophil numbers. Cytoxan$\sp{\rm R}$ (CY) was used to induce heteropenia in chickens. An anemia and leukopenia, characterized by heteropenia, lymphocytopenia, eosinopenia and basopenia, occurred on day 10. Heteropenia also occurred on day 12. Chickens were infected with MASS to synchronize heteropenia and peak epithelial damage. Tracheal epithelial damage was monitored by histopathology and heterophil infiltration by counting heterophils within tracheal epithelium and lamina propria. Although heteropenic chickens had fewer tracheal heterophils, there was no difference in tracheal epithelial damage of heteropenic and heterophil-intact, IBV-infected chickens. Heterophils most likely infiltrate in response to viral infection of the tracheal epithelium and are most likely not responsible for its damage.

Degree

Ph.D.

Advisors

Thacker, Purdue University.

Subject Area

Veterinary services|Pathology

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