Alveolar macrophages are tissue-resident or recruited cells with key functions in recognition of pathogens, initiation of host defensive ang protective inflammation,and in clearance of pathogens from the airways. However, macrophages are also responsible for efficient clearance of apoptotic neutrophils, termed efferocytosis, which is a prerequisite for the timely resolution of inflammation. In this study, the investigators aim to observe the change in alveolar macrophage function during acute lung injury.