FIGURE 1.

Resident alveolar macrophages in health (green) are influenced by the airway microenvironment to express a unique phenotype high in regulatory receptors that prevent responses to innocuous antigens. During inflammation airway macrophages are depleted and may be replaced in resolution by recruited monocytes that differentiate to macrophages and adapt to the airspace microenvironment (yellow). Generic processes include removal of extracellular matrix and efferocytosis of apoptotic cells. GAS: growth arrest specific protein; PS: phosphatidylserine; CCR: chemokine receptor.