Surfactant system of the lungs

Scarpelli, E.H. (1968) The Surfactant System of the Lung, Lea and Febiger, Philadelphia. 

Hydrophilic surfactant proteins A (SP-A) and D (SP-D), secreted by type II pneumocytes, interact specifically with a wide range of microorganisms and play important roles in the innate, natural defense system of the lung [16]. Both mRNA and protein levels of SP-A and SP-D increase dramatically in response to lung infection, injury and endotoxin challenge [17]. Type II pneumocytes also express class II major histocompatibility complex (MHC) antigens and intracellular adhesion molecule (ICAM-1), which may facilitate pulmonary immune responses [15]. 

Hamm H, Fabel H, Bartsch W. The surfactant system of the adult lung physiology and clinical perspective. Clin Invest 1992 70 637-657. 

Thus it is possible to estimate the time for surfactant adsorption required for the formation of black spots. Table 11.2 presents the clinical and threshold concentrations for total phospholipids (PL) and for disaturated phosphatidylcholine (DSPC) in each preparation. The most abundant PL of the lung surfactant system is DSPC, principally the DPPC species, which is believed the essential determinant of surfactant function in vivo [2], While DPPC is the only PL in EX, both IN and SU contain other PLs and small quantities of hydrophobic surfactant-associated proteins that may add to the desired functional properties of the material in situ. 

Phospholipids play an important role in lung functions. The surface active material to be found in the alveolar lining of the lung is a mixture of phospholipids, neutral lipids and proteins. Lowering of surface tension by the lung surfactant system and the surface elasticity of the surface layers assists alveolar expansion and contraction. Deficiency of lung surfactants in newborns leads to a respiratory distress syndrome and this led to the suggestion that instillation of phospholipid surfactants could cure the problem. 

For the treatment of lung surfactant deficiency in premature human infants suffering from respiratory distress syndrome, limited clinical trials were performed showing that liposomes in the lung-instilled intratracheally either as an aerosolized mist (Ivey et al., 1977) or as a suspension via an endotracheal tube (Fujiwara et al., 1980)—rapidly improved lung function. No adverse effects were observed as a result of the supplementation with surfactant-like material. It appears, therefore, that liposomes are a suitable system for the delivery of major phospholipid components of endogenous lung surfactant. 

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