It is part of the innate immune system and is used to opsonize bacterial cells in the alveoli marking them for phagocytosis by alveolar macrophages.
SP-A may also play a role in negative feedback limiting the secretion of pulmonary surfactant.
SP-A is not required for pulmonary surfactant to function but does confer immune effects to the organism.
If SP-A is injected into the uterus at 15 days, mice typically deliver early.
[3] In fact, the level of SP-A in a human uterus typically decreases during labor.