Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/21/2002
Publication Date: N/A
Technical Abstract: Surfactant Protein D (SP-D), a hydrophilic pulmonary surfactant collagenous calcium-dependent lectin with opsonizing activity, binds to surface glycoconjugates expressed by a wide variety of microorganisms such as Gram-negative bacteria, Influenza A virus, and various fungi as well as surface carbohydrates of leukocytes. The major sites of lung SP-D synthesis are bronchiolar and alveolar type II cells and non-ciliated respiratory epithelial (Clara) cells. Since a hallmark of bronchopneumonia is the initiation of inflammation in the bronchi and bronchoalveolar junction, we chose a classic ruminant model of bronchopneumonia caused by Mannheimia haemolytica to study the expression of SP-D within the bronchioles of infected lambs. Healthy weaned lambs were inoculated with either pyrogen-free saline (controls) or M. haemolytica intrabronchially via a fiberoptic bronchoscope. SP-D expression in lung was detected by immunohistochemistry during acute (1 day), subacute (15 days), and chronic (46 days) bronchopneumonia using a polyclonal rabbit anti-human SP-D antibody that was specific for ovine SP-D by SDS-PAGE and Western blot. The immunohistochemical staining was scored for the amount of staining within each cell (intensity) and the number of cells stained for SP-D within each bronchiole. At 15 and 45 days post-inoculation, areas of lung with increased peribronchiolar inflammatory cell infiltrate, epithelial cell hyperplasia, and tortuosity of the airway lumens had decreased intensity of SP-D staining and number of positive cells. A group of lambs with chronic bronchopneumonia received repeated (4) high doses (116 mM) of a non-toxic, water soluble retinoid (retinoyl b-glucuronide, RAG) given to resolve epithelial lesions; however, RAG did not alter/repair the lesions of established bacterial bronchopneumonia or alter the expression of SP-D. In conclusion, cell-associated SP-D protein expression significantly decreases within the hyperplastic epithelium of lungs from the infected animals during chronic pneumonia, and RAG does not alter SP-D expression.