CXCR4 and pulmonary fibrosis: In summary, we provide a new mechanistic insight into lung fibrosis and determine that megakaryocytes migrate to the BLM-injured lung through the CXCL12/CXCR4 axis and megakaryocytes promote the proliferation and trans-differentiation of fibroblasts partially through direct contact or TGF-β1 pathway (Fig. 7).