Effect of Pasteurella haemolytica (A1) capsular polysaccharide on sheep lung in vivo and on pulmonary surfactant in vitro.

Capsular polysaccharide (CP) of Pasteurella haemolytica (type A1) was first deposited by fiberoptic bronchoscopy into the lungs of sheep to examine lesions and changes in bronchoalveolar lavage cell populations and, later, was mixed with pulmonary surfactant to investigate alterations in physical properties or surface tension. At 22 hours after deposition, minimal lesions were seen in the lungs only at and contiguous to the site of CP deposition in 2 of 4 sheep. Microscopically, alveoli and interlobular septa were filled with edema fluid. Terminal airways and alveoli contained a moderate amount of neutrophils that varied between sheep. Significant differences in number or type of bronchoalveolar lavage cells were not observed in the weekly lavages between each group or among sheep within each group, either before or after deposition of CP or physiologic saline solution. After 6 hours of incubation at 37 C, CP-surfactant mixtures were examined with a surface tensiometer and centrifuged in sucrose gradients. The CP bound to surfactant, resulting in formation of a precipitate with a surface tension of 31.6 +/- 0.1 dynes/cm and a density of 1.07 to 1.08 g/ml. Lipopolysaccharide of P haemolytica, used as a control, also bound to surfactant, resulting in a complex with a surface tension of 57.7 +/- 0.4 dynes/cm and a density of 1.06 to 1.10 g/ml. Surfactant alone had a surface tension of 32.6 +/- 0.2 dynes/cm and density of 1.05 to 1.06 g/ml. The CP appears by itself not to be a direct major factor in the lung damage that develops in cases of pneumonic pasteurellosis.(ABSTRACT TRUNCATED AT 250 WORDS)