Lipid composition of alveolar macrophage plasma membrane during postnatal development.

This study was undertaken to define the age-related alterations in lipid composition that resident rabbit alveolar macrophages (AM) undergo during postnatal development. The eventual goal is to correlate these changes with the functional maturation of these cells. The number of AM recorded from total lung lavages rose markedly during the first 14 days of life, from 4.9 X 10(5) to 1.1 X 10(7). Adult lungs yielded 1.1 X 10(8) AM. A gradual but significant increase in fluorescence polarization (P) was observed during development when purified AM plasma membranes were tagged with the probe 1,6-diphenyl-1,3,5 hexatriene trimethyl ammonium. The rise ranged from a mean P value of less than or equal to 0.22 to 0.24 (p less than 0.001) for AM plasma membranes from rabbits 1- or 7-day-old to 30- or 150-day-old rabbits, respectively. This finding suggests that the fluidity of the AM plasma membrane decreased during postnatal development. Palmitic, stearic, oleic, and linoleic acids were the most prevalent fatty acids found in the neutral lipid fraction of the AM plasma membrane throughout development. The content of stearic acid rose from 10 to 16%, arachidonic acid rose from 2.8 to 9%, myristic acid decreased from 3.2 to 1.3%, palmitic acid decreased from 42 to 36%, and oleic and linoleic acids changed relatively little during the first 30 days of life. The levels of docosatetraenoic and docosapentaenoic increased gradually during the first 14 days of life, and by 30 days of life the levels declined to that observed at birth. The sum of these changes resulted in an increase in the ratio of unsaturated to saturated fatty acids (1 to 1.15) in the neutral lipid fraction. During the first month of life, the neutral lipid fatty acid pool in the total lipid fraction of AM plasma membrane increased from 12 to 18 mole %, cholesterol increased from 7 to 14 mole %, and total phospholipids decreased from 81 to 67 mole %. These changes resulted in increasing the cholesterol to phospholipid ratio from 0.09 at birth to 0.23 by 150 days of life. The levels of all three major lipid fractions were comparable at 30 days and 150 days of life. Adult levels of choline phosphoglycerides, the predominant phospholipid, were observed by 7 days of life to have decreased from 47 to 34.5 mole %, and the levels of ethanolamine phosphoglycerides and sphingomyelin increased from 17.5 to 25 mole % and from 9 to 13 mole %, respectively. Adult levels of lyso-bis-phosphatidic acid were reached by 30 days of life increasing from 8.2 to 17.8 mole %.(ABSTRACT TRUNCATED AT 400 WORDS)