Stereological and biophysical characteristics of the ovine surfactant system and its changes caused by ovine pulmonary adenocarcinoma

Abstract

Surfactant covers the inner surface of lung alveoli and lowers the surface tension to prevent alveoli from collapsing. A lack of surfactant or its dysfunction causes dyspnea. The Jaagsiekte Sheep Retrovirus (JSRV) causes ovine pulmonary adenocarcinoma (OPA), whose typical clinical appearance is fluid running from nostrils. This fluid might contain surfactant as alveolar type II pneumocytes (AEII) are target cells for JSRV. Therefore, the progressive dyspnea during OPA might be caused partially by surfactant alterations.Bronchoalveolar and intracellular surfactant as well as the biophysical function of surfactant were analyzed in OPA sheep and controls. Transmission electron microscopy and stereological methods were used to characterize ultrastructure and distribution of surfactant subtypes in AEII and bronchoalveolar lavage fluid (BALF). Pulsating Bubble Surfactometry enabled studying the surface activity of the surfactant, while lung volumes were detected by computed tomography.The methods used are suitable to determine intraalveolar and intracellular surfactant subtypes in OPA sheep and controls. OPA sheep showed more lamellar body-like forms, multivesicular vesicles and tubular myelin in BALF compared to controls. These higher amounts of active surfactant subtypes might be a consequence of a higher surfactant production and release. Surfactant subtypes in AEII of OPA sheep showed smaller and more immature lamellar bodies compared to controls. The surfactant surface activity of OPA sheep does not show obvious defects. In conclusion, the general quality of surfactant in OPA appears to be equivalent to surfactant produced in controls, however, dyspnea of OPA might be triggered by quantity of fluid production.