Alveolar Macrophages Maintain Tissue Localization and Gain Enhanced Anti-Tumor Activity in Lewis Lung Carcinoma-Reprogrammed Lung Microenvironment

The role of alveolar macrophages (AMs) in lung carcinogenesis has been extensively studied, yielding significant insights. However, the status of AMs in tumor-bearing lungs remains incompletely characterized. Using orthotopic Lewis Lung Carcinoma (LLC) mouse models, we found that tumors induced an inflammatory extra-tumoral lung microenvironment (ETLME), distinct from the immunosuppressive tumor microenvironment (TME). T cells with an exhaustion phenotype and tumor-associated macrophages (TAMs) mainly accumulated in the TME rather than the ETLME. Surprisingly, AMs were absent from the tumor lesions and remained in the lung tissues, but they displayed a more active dynamic balance between proliferation and death in ETLME. Furthermore, AMs presented an activated phenotype characterized by upregulation of CD11b and downregulation of Siglec-F, elevated expression of inflammatory genes, and enhanced phagocytic and efferocytotic activity. Notably, AMs in ETLME retained their lipid metabolism capacity and responsiveness to external stimuli. More importantly, LLC-experienced AMs display enhanced anti-tumor ability. These findings indicate that AMs maintain their tissue localization and functional integrity within the ETLME. Overall design: BAL fluid was collected from the tumor-bearing and control mice. AMs were resuspended at a density of 1×105 cells/mL in complete DMEM (supplemented with 10% FCS), seeded into a 24-well plate (1 mL/well). Non-adherent cells were then removed after incubating for 30 min. AMs were stimulated for 4 hours with DMEM medium containing 400 ng/mL lipopolysaccharide (LPS) from E. coli 055:B5 (InvivoGen, tlrl-b5lps) or in LPS-free medium (as control) for 4 hours. RNA-seq samples were generated from 2-3 mice.