Factors Related to the Appearance of Alveolar Macrophages in the Developing Lung

Abstract

The numbers of alveolar macrophages (AM) are low in utero and increase rapidly after birth. Factors related to the appearance of AM were analyzed in the lungs of term and preterm monkeys (Macaca nemestrina). The numbers of AM were greater at birth in term than in preterm monkeys (P < 0.01), and they increased with postnatal age in term animals (r = 0.86) and in preterm animals without hyaline membrane disease (HMD) (r = 0.79). In contrast, the numbers of AM did not increase with postnatal age in preterm animals with HMD (r = 0.17). By multivariant analysis, AM numbers correlated most strongly with a combination of 2 variables: lavage fluid phospholipid and absence of HMD (r = 0.996). Preparations of alveolar surface-active material from newborn monkeys, and to a lesser degree from adult monkeys, stimulated migration and polarization of monkey Am and blood monocytes in vitro. The migration-stimulating factor(s) in alveolar surface-active material had an apparent MW > 10,000, and appeared not to be a lipoxygenase product of arachidonic acid metabolism. A correlation between factors regulating lung pressure-volume stability and AM numbers was indicated. They were consistent with a potential role for components of alveolar surface-active material in regulating the perinatal increase in AM.