Function of lung surfactant and its deterioration

: Lung surfactant(LS) is a mixture of several lipids and four apolipoproteins(SP-A, -B, -C and -D) and lowers surface tension at air-liquid interface of alveoli. Most of LS is synthesized and secreted by alveolar type II cells. Although lamellar bodies are storage granules of LS, each component appears to take independent intracellular routes to reside in the granules. Patients with infantile respiratory distress syndrome(IRDS) or acute respiratory distress syndrome(ARDS) develop fatal respiratory failure due to lack of LS. In addition, acute phase of interstitial pneumonia also shows deterioration of LS and increased alveolar surface force resulting in decreased lung compliance. SP-A and SP-D are used as serum marker to evaluated activity of interstitial lung diseases. Recently, growing evidences are accumulating that LS plays a role in innate host defense in the lung against large species of bacteria, mycoplasma, and viruses.