Published ahead of print on November 25, 2003, doi:10.1165/rcmb.2003-0127OC Am. J. Respir. Cell Mol. Biol., Volume 30, Number 5, May 2004, 751-758 A more recent version of this article appeared on May 1, 2004
Submitted on April 7, 2003 A common pathway for the uptake of surfactant lipids by alveolar cellsDavey L Poelma1,1 Dept. of Anesthesiology, Erasmus MC - Faculty, Rotterdam, The Netherlands, 2 Laboratory of Pediatrics, Erasmus MC - Faculty, Rotterdam, The Netherlands * To whom correspondence should be addressed. E-mail: j.vaniwaarden{at}erasmusmc.nl.
The uptake of different surfactant lipids: dipalmitoylphosphatidylcholine (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 macrophages) was studied in vitro. Fluorescent labeled liposomes containing 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, phosphatidylcholine, 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, demonstrated 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, less alveolar type II cells take up DPPC whereas there are no differences for the alveolar macrophages in the number of cells involved in the uptake. Competition experiments with Texas-Red labeled liposomes and either DPPC liposomes or PI liposomes labeled with Bodipy indicated that all these liposomes are internalized via the same pathway by alveolar cells. Thus, lipid composition directly influences the (re)uptake of surfactant.
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