MHCIIhi neutrophils were shown to facilitate the metastasis of breast cancer to the lung, which were recruited by C-C Motif Chemokine Ligand 2 (CCL2) from lung tissues with chronic pulmonary infection, acts as the vital bacterial-immune mediator to bridge chronic infection and lung metastasis of breast cancer in a cell-intrinsic manner in a mouse model (38). The gene discussed is CCL2; the disease is breast cancer.