A Common Pathway for the Uptake of Surfactant Lipids by Alveolar Cells

The uptake of different surfactant lipids—dipalmitoylphosphatidyl-choline (DPPC), phosphatidylglycerol (PG), or phosphatidylinositol (PI)—and liposomes with a surfactant-like composition by alveolar type II cells (alveolar type II cells) and macrophages (alveolar macro-phages) was studied in vitro. Fluorescent-labeled liposomes con-taining either 86 % of the studied lipid, i.e., DPPC, PG, PI, and 6% labeled phosphatidylethanolamine (PE) and 8 % cholesterol or a lipid mixture similar to surfactant (DPPC, PG, PI, phosphatidylcho-line, PE, and cholesterol in a weight ratio of 55:8:2:21:8:6) were incubated with alveolar macrophages and alveolar type II cells. The cell-associated fluorescence assessed by flow cytometry demon-strated a higher uptake of PG and PI by both alveolar macrophages and alveolar type II cells, and a lower uptake of DPPC by alveolar macrophages. In addition, fewer alveolar type II cells take up DPPC, whereas there are no differences for the alveolar macrophages i