Surfactant proteins A and D are part of the innate immune system and play crucial roles in lung function. They are produced by the alveolar type II cells in the lungs and are essential for maintaining the surface tension of the alveoli, preventing their collapse during breathing. These proteins also help in the clearance of pathogens and debris from the lungs. Both proteins belong to a family known as collectins, which are involved in recognizing and binding to specific carbohydrates on pathogens. By doing so, surfactant proteins A and D enhance the immune response, facilitating the opsonization and phagocytosis of harmful microorganisms, thus contributing to respiratory health.