The human lung surfactant proteins A (SP-A) and D (SP-D) interact with apoptotic target cells by different binding mechanisms

The role of the lung surfactant proteins SP-A and SP-D in immune defence is well established. They bind to foreign organisms that invade the lungs and target them for phagocytic clearance by resident alveolar macrophages. SP-A and SP-D also bind to various apoptotic cells and facilitate their phagocytic uptake. To date, the molecular mechanisms by which the lung surfactant proteins interact with apoptotic cells and phagocytes are poorly understood.