The lower respiratory tract (LRT) of 6 adult sheep was fixed in either isotonic formalin-acetic acid or neutral buffered formalin in order to study the heterogeneity, morphology and density of mast cells (MCs). Two subtypes of MCs were found, one histochemically similar to connective tissue MCs (formalin resistant) and the other similar to mucosal MCs as found in the intestine of the rat (formalin sensitive). Although both subtypes were present at all levels of the tract, formalin-sensitive MCs were significantly more abundant (p < 0.01) at all levels, and their density increased distally from the trachea to the peripheral lung. The formalin-sensitive MCs were predominantly located in the alveolar septa and in the superficial lamina propria of airways and less frequently within the airway epithelium. The MCs in the ovine LRT were found to be morphologically heterogeneous at both the light-microscopic and electron-microscopic levels. These findings indicate that ovine respiratory tract MCs have similarity to human lung MCs, and therefore potential for use as a model for the study of human allergic disease of the respiratory system.

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Abstract. Eight colostrum-deprived lambs were inoculated intratracheally with ovine isolates of Bordetella parapertussis. Fluids obtained by bronchoalveolar lavage had a large increase in total cell counts 24 hours after inoculation; up to 93% of cells were neutrophils. From 3 days after inoculation, the number of alveolar macrophages in lavage samples was markedly increased. From 5 days onwards, many alveolar macrophages had moderate to severe cytoplasmic vacuolation. Topographically, tracheal and bronchial epithelium was covered by a large amount of inflammatory exudate 24 hours after inoculation. Later, the tracheobronchial epithelium showed focal extrusions from ciliated cells, which were occasionally associated with B. parapertussis organisms. Ultrastructurally, cytopathological changes associated with B. parapertussis infection were mild focal degeneration of airway epithelium with slight loss of cilia, moderate to severe degeneration of type I and type I1 alveolar epithelial cells, and focal inflammation in the lungs. These results suggest that the primary targets of B. parapertussis infection are alveolar macrophages and the epithelial cells of bronchioles and alveoli.Bordetella parapertussis is one of the causative agents of whooping cough, a noninvasive infection of the lower respiratory tract of humans. l 9 Recently, this organism has also been isolated in New Zealand from the respiratory tract of both healthy lambs and lambs affected with chronic non-progressive pneumonia (CNP). Subsequent studies showed that the organism could attach to cilia and damage the ciliary epithelium of ovine tracheal organ cultures3 and caused a subacute bronchopneumonia in mice by intranasal inoculation. l oIn a previous study we described histopathologic and bacteriologic observations on experimental B. parapertussis infection in colostrum-deprived lambs and demonstrated the pathogenicity of B. parapertussis for the ovine respiratory tract. Major lesions in infected lambs were those of acute mild tracheobronchitis and acute bronchopneumonia. However, no specific morphologic interface was found between the infected respiratory tract and the organisms, and the pathogenesis of the lesions remains unknown. We now report observations on bronchoalveolar lavage samples and ultrastructural features in experimental ovine pneumonia caused by B. parapertussis, which were carried out in order to better understand the potential importance of this organism in the ovine respiratory disease. Materials and MethodsTwelve colostrum-deprived, 1 -week-old lambs were assigned to two age-matched groups. Lambs in Group 1 ( n = 4) were given 5 ml of sterile phosphate buffered saline (PBS) intratracheally as controls; lambs in Group 2 (n = 8) were given 5 ml of B. parapertussis suspension with a viable cell count of 2.3 x 1 O6 colony-forming units/ml intratracheally. Lambs were killed on post-inoculation days (PID) 1, 3, 5, and 9.At necropsy, one lamb from each group was used for a cytological study of bronchoalveolar lavage (BAL). The trachea wa...