Host Defenses in the Fetus and Neonate: Studies of the Alveolar Macrophage during Maturation

Abstract

In recent years, an increasing investigative effort has been applied to the study of host defenses in the fetus and neonate.1, 2 The importance of this knowledge to medicine includes its immediate application in the perinatal period as well as its implications as antecedents of end stage disease in the adult. One of the most important initial defense systems is provided by phagocytic cells and of these the alveolar macrophage assumes central importance in the lung. Shown in Fig 1 is a schematic representation of the interactions of cells of the immune system with the environment and depicts the central role of the alveolar macrophage. For the past several years, we have been interested in assessing factors relating to phagocytic function in both man3, 4 and the experimental animal.5-7 These studies arose from the well known clinical and experimental observations which suggested that infections, particularly those caused by bacterial organisms, are more frequently encountered in the young infant. The major emphasis of these studies in recent years has been the alveolar macrophage. The choice of this cell type is based upon the frequency and importance of respiratory tract infections in pediatrics. It would be neither possible nor appropriate for me to review all the investigations which have been carried out by many workers along these lines. Instead, I have chosen to present the results of three lines of our recent investigations dealing with the morphologic, biochemical, and functional maturation of the alveolar macrophage (AM) and their clinical application to current pediatric problems.