An alveolar macrophage (or dust cell) is a type of macrophage, a professional phagocyte, found in the pulmonary alveoli, near the pneumocytes, but separated from the wall. Activity of the alveolar macrophage is relatively high, because they are located at one of the major boundaries between the body and the outside world. They are responsible for removing particles such as dust or microorganisms from the respiratory surfaces. The alveolar macrophage is the third cell type in the alveolus, the others are the type I and type II pneumocytes.