AMΦ, which are located in the alveolar compartment of the lungs, provide a key initiation signal for ALI212223. Previous studies have shown that the later phase of ALI is neutrophil-dependent24, while AMΦ contribute to the acute phase of lung injury. Once activated by bacteria or viruses, AMΦ generate and release a multitude of mediators, such as cytokines (IL-6, TNF-α) and chemokines (MCP-1, MIP-2)2526. These mediators act as chemoattractants for the migration of large numbers of activated inflammatory cells, such as monocytes and neutrophils, into the airspaces27.