Pulmonary interstitial macrophages are required to mediate the pro-tumorigenic effects of IL-9

We demonstrate that deficiency of IL-9 signaling inhibits lung tumor growth in multiple models. In defining the IL-9-responsive cells in the lung tumor models, we found IL-9 regulates lung heterogeneity by inhibiting alveolar macrophage and promoting the expansion of both CD11c+ and CD11c- interstitial macrophage populations. Interstitial macrophages are a critical IL-9-responsive population that is required to promote lung tumor growth. Mechanistically, the IL-9/macrophage axis requires arginase1 (Arg1) to mediate tumor growth. Adoptive transfer of Arg1+ but not Arg1- lung macrophages to Il9r-/- mice dramatically increases the tumor growth. In parallel, the elevated expression of IL-9R and Arg1 in human tumor associated macrophages is correlated with poor prognosis among lung cancer patients. Moreover, targeting IL-9 signaling in lung macrophages limited lung tumor growth. Exam the gene expression of interstitial macrophages in tumor bearing WT and Il9r knock-out mice