Surfactant/SP-A [C5]

Pulmonary surfactant is a complex mixture of phospholipids and proteins that is secreted from type II cells in alveoli and reduces the surface tension at the alveolar air-liquid interface, providing alveolar stability necessary for normal ventilation. Four distinct proteins isolated from pulmonary surfactant are termed surfactant proteins A, B, C, and D. SP-A (28-36kDa) and SP-D (43kDa) are collagenous carbohydrate-binding proteins, whereas SP-B (8-9kDa) and SP-C (4kDa) are non-collagenous hydrophobic proteins. SP-A is a distinct marker of type II pneumocyte differentiation.