Flow cytometric analysis of macrophages and dendritic cell subsets in the mouse lung

The lung hosts multiple populations of macrophages and dendritic cells, which play a crucial role in lung pathology. The accurate identification and enumeration of these subsets are essential for understanding their role in lung pathology. Flow cytometry is a mainstream tool for studying the immune system. However, a systematic flow cytometric approach to identify subsets of macrophages and dendritic cells (DCs) accurately and consistently in the normalmouse lung has not been described. Here we developed a panel of surface markers and an analysis strategy that accurately identify all known populationsofmacrophages andDCs, andtheir precursors in the lung during steady-state conditions and bleomycin-induced injury. Using this panel, we assessed the polarization of lungmacrophages during the course of bleomycin-induced lung injury. Alveolar macrophages expressed markers of alternatively activated macrophages during both acute and fibrotic phases of bleomycin-induced lung injury, whereasmarkers of classically activatedmacrophageswere expressed only during the acute phase. Taken together, these data suggest that this flow cytometric panel is very helpful in identifying macrophage and DC populations and their state of activation in normal, injured, and fibrotic lungs.