Smaller sized particles are preferentially taken up by alveolar type II pneumocytes

The uptake of both lung surfactant and other particles from the alveolar space plays an essential role in surfactant metabolism, host defense and may be of relevance for targeting drugs into alveolar cells. To better understand the effect of particle size on the uptake by type II pneumocytes, rat type II cells in primary culture were investigated. We observed that inert latex particles of 15 nm were taken up to a much greater extent than bigger particles. No strong size dependency was observed in the range from about 200 to 1000 nm. A similar observation was made with a natural lipid extracted lung surfactant which was taken up to a greater extent when prepared at particles of about 100 nm than a preparation with a particle size range from about 200-2000 nm. Alveolar type II cells take up smaller particles better than larger ones, but the size selectivity is rather limited. These type II cell properties may contribute to a preferential elimination of the smaller particle fractions from the alveolar space.