Interleukin 4 controls the role of macrophages in pulmonary metastatic tumor cell seeding and growth
Metastasis is the systemic manifestation of cancer and the main cause of death from breast cancer. In mouse models of lung metastases, recruitment of classical monocytes from blood to the lung and their differentiation to metastasis-associated macrophages (MAMs) facilitate cancer cell extravasation, survival, and growth. Ablation of MAMs or their monocytic progenitors inhibits metastasis. We hypothesized that factors controlling macrophage polarization modulate tumor cell extravasation in the lung. We evaluated whether signaling by Th1 or Th2 cytokines in macrophages affected trans-endothelial migration of tumor cells in vitro. Interferon {gamma} and LPS inhibited macrophage-dependent tumor cell extravasation while the Th2 cytokine interleukin-4 (IL4) enhanced this process. We demonstrated that IL4 receptor (IL4r) null mice develop fewer and smaller lung metastasis. Adoptive transfer of wild type monocytes to IL4r deficient mice rescued this phenotype. IL4 signaling in macrophages controls the expression of the chemokine receptor CXCR2, necessary for IL4-mediated tumor cell extravasation in vitro. Furthermore, IL4 signaling in macrophages transcriptionally regulates several other genes already causally associated with lung metastasis including CCL2, CSF1, CCR1, HGF and FLT1. The central role for IL4 signaling in MAMs was confirmed by high-resolution intravital imaging of the lung in mice at the time of metastatic seeding, which showed reduced physical interaction between tumor cells and IL4r-deficient macrophages. This interaction enhances tumor cell survival. These data indicate that IL4 signaling in monocytes and macrophages is key during seeding and growth of breast metastasis in the lung as it regulates pro-tumoral paracrine signaling between cancer cells and macrophages.