Surfactant proteins A and D in pulmonary diseases of preterm infants.

Immaturity of the pulmonary and immune systems represents an important risk factor for increased morbidity and mortality in neonates. Surfactant protein (SP)-A and SP-D, linking molecules between these two systems, are critical for lung homeostasis as they regulate surfactant metabolism and host immunodefense activities in innate and adaptive immunity. Preterm neonates with respiratory distress syndrome showed lower concentrations of SP-A and SP-D, and the administration of exogenous surfactant was found to strengthen the secretion of SPs. Low levels of SP-A and SP-D also correlated with a higher risk of infection and development of bronchopulmonary dysplasia. Moreover, SP-A- and SP-D-enriched surfactant formulations were more resistant to the inhibitory action of the plasmatic proteins in animal models. Based on these assumptions, new-generation surfactants, enriched with SP-A and/or SP-D, may enhance the function of immune system and lungs in neonates, potentially improving the clinical outcome.