Browsing by Author "Chen, Wangxue"

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    Experimental airway hypersensitivity in sheep : a model for asthma : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Pathology at Massey University
    (Massey University, 1990) Chen, Wangxue
    This study aimed to establish an animal model for human bronchial asthma using locally bred Romney sheep. It was then planned to determine whether or not morphological and inflammatory factors in the ovine respiratory tract are associated with a predisposition to allergic bronchial hypersensitivity induced by inhaled Ascaris suum antigen. The skin and airway responses to a commercial A. suum antigen were tested in adult Romney sheep from two local farms with and without previous exposure to pigs. Ninety percent of 101 adult sheep tested showed an immediate skin reaction, and about 70% of 43 adult sheep with positive skin reactions showed an immediate airway response, reflected as a significant increase in airway resistance and/or decreased dynamic lung compliance. Among these 43 sheep, 21 showed changes in both airway resistance and dynamic lung compliance (Group A); ten only in dynamic lung compliance (Group B) and 12 were non-responders (Group C). No significant changes were recorded when the same animals were given an aerosol of phosphate buffered saline. Although the sheep with previous exposure to pigs showed significantly greater skin reactions than those without exposure to pigs, they showed no significant differences in airway response to antigen inhalation. In addition, there was no correlation between the degree of skin reaction and the magnitude of bronchoconstriction. Since no information was available on the respiratory tract-associated lymphoid tissue and cells in healthy sheep, study of this tissue and its associated epithelium was a prerequisite for studies of the morphological and inflammatory mechanisms involved in the development of allergic airway hypersensitivity. The ovine respiratory tract has five forms of lymphoid tissue; intra-luminal, intraepithelial, scattered forms, and dense and nodular aggregations; the dense and nodular aggregations being confined to the pharyngeal tonsil and bronchioles. Morphologically well-developed lymphoepithelium (M cells) is present only in the pharyngeal tonsil region, and absent in the lower respiratory tract. The M cell of the ovine pharyngeal tonsil is ultrastructurally and functionally similar to that in other mucosal tissues of this and other species, but its development and maturation takes place earlier than the bronchus-associated lymphoid tissue. Mast cells in the lower respiratory tract of normal sheep are morphologically heterogeneous, and both formalin-sensitive and formalin-resistant types can be identified. The morphological and histochemical features of formalin-sensitive mast cells are similar to those from the human respiratory tract in several respects which enhances the use of the sheep model in the study of human allergic respiratory disease. A morphometric comparison of airway structure and inflammatory components was conducted between the three groups of sheep with varying airway hypersensitivity. The epithelium of the small airways was significantly thinner and contained fewer goblet cells in the hypersensitive sheep (Groups A and B; than in non-reacting sheep (Group C). Mast cells from the hypersensitive sheep had a significantly greater volume density of secretory granules than those from non-reacting sheep. However, no morphological difference was found in the epithelial integrity of airways between hypersensitive and non-reacting sheep, and the permeability of tracheobronchial epithelium to horseradish peroxidase was of the same order in all groups. Similarly, the airway wall was not significantly thicker in hypersensitive sheep than in non-reacting sheep, and the shortening of smooth muscle required to cause complete airway closure was similar. The numerical density of mast cells, eosinophils, neutrophils and lymphocytes in the airways and lung was not significantly different between the groups. These observations indicate that the Ascaris-induced airway response seen in Romney sheep is similar in several respects to that seen in human asthmatics and these sheep can therefore be used as an animal model to study human asthma. The current findings suggest that the presence of relatively low goblet cell density, thin epithelium, and high volume density of mast cell secretory granules in the small airways and lung may be important inherent factors responsible for the development of airway hypersensitivity in these sheep. It is concluded that most of the other morphological features observed in asthmatics and animal models are likely to be the result of allergic airway reactions rather than a fundamental difference between potentially allergic and non-allergic subjects.
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    Experimental pneumonia induced by a Bordetella parapertussis-like organism in the ovine and murine lung : a thesis presented in partial fulfillment (70%) of the requirements for the degree of Master of Philosophy in Veterinary Pathology at Massey University
    (Massey University, 1987) Chen, Wangxue
    Thirty-four specific pathogen-free (SPF) Swiss mice were intranasally inoculated with a suspension containing about 3 x 10 7 colony-forming units (CFU)/ml of a B. parapertussis-like organism isolated from pneumonic ovine lung. Eleven per cent of the animals died between 2 and 3 days of inoculation and over 90% of infected mice developed a subacute bronchopneumonia morphologically similar to early lesions of naturally-occurring ovine chronic non-progressive pneumonia (CNP). The sequential pulmonary changes were examined by light microscopy and transmission electronmicroscopy from 12 hr to 29 days after inoculation. The early stages were characterized by alveolar septal congestion and oedema, focal intra-alveolar haemorrhage, and intra-alveolar and septal infiltration by neutrophils and macrophages. Later, hyperplasia of perivascular and peribronchiolar lymphoid tissue and the deposition of collagen in the interalveolar septa were prominent. The bronchial and bronchiolar epithelium remained intact throughout the experiment, but bronchiolar lumina became occluded by inflammatory exudate at an early stage. Ultrastructural changes consisted of the degeneration of the alveolar type I and type II epithelial cells and marked degeneration of alveolar macrophages. Pure cultures of the B. parapertussis-like organism were consistently recovered from mouse lungs 12 hr to 6 days after inoculation. Both intact and degenerating organisms were found free in alveolar spaces and within phagocytic vacuoles of alveolar macrophages. However, replication of organisms was not observed at any stage of infection and no special association was observed between organisms and the ciliated or non-ciliated respiratory epithelium. Injury to ovine respiratory tract was demonstrated when a similar bacterial suspension to that given to the mice was given by intratracheally to colostrum-deprived lambs. The lesions produced in the pulmonary parenchyma of the lambs were similar to those seen in both early naturally-occurring ovine CNP and the experimental infection with this organism in mice. They consisted of an acute mild tracheobronchitis, severe alveolar collapse and acute bronchopneumonia which developed within 24 hr and was most severe at 1 to 3 days after inoculation. Ultrastructurally, the alveolar epithelium exhibited extensive degenerative changes and necrosis of individual epithelial cells. Topographical studies revealed extensive coverage of the infected tracheobronchial epithelium with a dense layer of inflammatory cells mixed with mucus, and focal extrusion of ciliated cells. Occasionally, moderate numbers of the B. parapertussis-like coccobacilli were seen closely associated with cilia. Inoculated lambs showed a marked elevation in the numbers of cells in bronchoalveolar lavage 24 hr after infection. Up to 93% of the cells in the lavage at 24 hr were neutrophils. However, no close interation between phagocytic cells and the organises was detected. Many of the macrophages in the lavage exhibited cytoplasmic vacuolation from five days after inoculation onwards. Blood leucocyte and neutrophil counts in infected lambs gradually rose to reach peaks at five and three days after inoculation, respectively. The B. parapertussis-like organism was recovered in pure culture from the nasal cavity of lambs killed on days one, three, five and nine. The viable bacterial count in bronchoalveolar lavage fluid decreased from 24 hr to 5 days with almost complete elimination of organisms nine days after inoculation. The retention of the B. parapertussis-like organism in the mouse trachea was compared to that in the mouse lung from 0 to 48 hr after intranasal inoculation. Although there was greater bacterial deposition in the trachea than the lung there was a faster clearance from the trachea. At 48 hr after instillation, almost all organisms were eliminated from the trachea but about 45% of organisms were retained in the lung. The current investigation has shown that the B. parapertussis-like organism can infect SPF mice and colostrum-deprived lambs and induce a subacute bronchopneumonia. The morphological changes seen suggest that this organism has the potential to predispose the ovine respiratory tract to further infection by other microorganisms and that the organism itself may also be able to cause severe pulmonary damage. The relevance of these observations to the problem of CNP in sheep in the field has yet to be determined.