All are functions of surfactant except:

Role of surfactant: Reduces surface tension and increases compliance- reduced work of breathing Keeps alveolar size relatively uniform i.e., prevents alveolar collapse and stabilises alveoli. In lungs, all alveoli do not have same diameter, alveoli size also changes during inspiration and expiration, and alveoli are interconnected with each other by pores of Kohn. Without surfactant, small alveoli would empty into communicating larger ones, resulting in atelectasis and reduction in the total alveolar surface area available for diffusion of O2 and CO2 3. Minimizes fluid accumulation in the alveolus (keeps alveoli dry and prevents pulmonary edema). Just as the surface tension forces tend to collapse alveoli, they also tend to suck fluid out of the capillaries. In effect, the surface tension of the curved alveolar surface reduces the hydrostatic pressure in the tissue outside the capillaries. By reducing these surface forces, surfactant prevents the transudation of fluid. 4. Provides innate immunity: SP-A and SP-D, belong to a family of proteins called collectins. They stimulate phagocytosis, chemotaxis, and regulate release of cytokines by immune cells.