Characterization of surfactant alterations in pigs infected with Actinobacillus pleuropneumoniae

Surfactant, a surface active complex of phospholipids and proteins located at the inner surface of alveoli and small conducting airways is necessary for breathing. Bacterial respiratory tract infections frequently lead to surfactant alterations and to an increase in surface tension. Pigs, often used in experimental lung research, could suffer from severe pleuropneumonia, a highly contagious disease often characterized by sudden onset, short clinical course, high morbidity, and high mortality. It is caused by the gram-negative bacterium Actinobacillus pleuropneumoniae (A.pp.). This study tests the hypothesis that also in the subacute stage pathomorphological lung alterations are accompanied with increased inactive surfactant components. Clinical lung scores, functional and ultrastructural analysis of porcine surfactant were performed in pigs before infection and in the subacute state of infection. Clinical signs were determined using inter alia different subscores. Surfactant was isolated from the BALF for functional and quantitative ultrastructural studies.

In the subacute stage clinical, ultrosonographic and radiographic scores as well as the overall Respiratory Health Score showed significantly higher values than before infection. However, surfactant surprisingly contained more active surfactant subtypes and significantly less inactive subtypes such as unilamellar vesicles. The quantity of multilamellar vesicles with unclear function did not differ. The minimal surface tension of surfactant before and after infection was comparable.

Thus, in spite of continued severe lung tissue alterations the surfactant system show signs of recovery. This may be the result of an effective adaption to inflammatory lung disorders caused by swine-specific pathogens.