Introduction: Lung Surfactant—Phospholipids and Apoproteins

Evidence accumulated over the past 50 years has indicated that the alveolar surface of the lung is lined by a material that when tested in vitro has marked surface activity [1, 2]. This material, called the lung surfactant, can be isolated in relatively pure form through centrifugation procedures such as those described by King and Clements [3]. Surfactant as isolated by this method is a mixture of lipids, proteins, and carbohydrate [4, 5], with phospholipid accounting for 75-80% of the total weight (Table 1). Dipalmitoyl phosphatidylcholine accounts for nearly half and other phosphatidylcholines account for approximately one-third of the total phospholipid. Recently, considerable attention has focussed on phosphatidylglycerol, which comprises only 6-12% of the phospholipid [6], but even this amount is uniquely high compared with other tissues. Cholesterol, the major neutral lipid present in surfactant, accounts for 8% or more by weight of the total surfactant. These lipid components are responsible for surface activity of the surfactant and presumably account for its putative physiologic role in stabilizing the lung alveoli.