CXCR4 and pulmonary fibrosis: B cells engage with senescent neutrophils through β integrins (CD11b–CD18) to promote their apoptosis and clearance, preventing excess neutrophils and reducing inflammation and fibrosis. The CXCR4 antagonist AMD3100 decreases B cell and neutrophil presence in the lungs, directly slowing pulmonary fibrosis progression.