Exogenous surfactant changes the phenotype of alveolar macrophages in mice

Alveolar macrophages are essential for the maintenance of surfactant homeos tasis. We asked whether surfactant treatment would change alveolar macropha ge number and whether the alveolar macrophage phenotype would become activa ted or apoptotic when challenged in vivo with exogenous surfactant. Surfact ant pool size in mice was increased by repetitive surfactant treatments con taining 120 mg/kg (110 mmol/kg) saturated phosphatidylcholine. The number o f alveolar macrophages recovered by alveolar lavage decreased after the fir st dose by 49% and slightly increased after the second and third doses. Up to 28.5% of the macrophages became large and foamy, and their appearance no rmalized within 12 h. Surfactant treatment did not increase the percent of apoptotic or necrotic cells. The alveolar macrophages were not activated as indicated by no change in expression of CD14, CD16, CD54, CD95, and scaven ger receptor class A types I and II after surfactant treatment. Surfactant treatment in healthy mice transiently changed the phenotype of alveolar mac rophages to large and foamy without indications of changes in the surface m arkers characteristic of activation.