The chemokine CCL1 facilitates pulmonary fibrosis by promoting macrophage migration and M2 polarization.

Macrophage M2 polarization has been identified in the pathogenesis of pulmonary fibrosis (PF), but the mediators that drive the macrophage M2 program in PF need to be clarified. We showed that the expression of AMFR and CCR8, two known receptors of CCL1, was increased in macrophages from lungs of mice with bleomycin (BLM)-induced PF. Deficiency in either AMFR or CCR8 in macrophages protected mice from BLM-induced PF. In vitro experiments revealed that CCL1 recruited macrophages by binding to its classical receptor CCR8 and drove the macrophage M2 phenotype via its interaction with the recently identified receptor AMFR. Mechanistic studies revealed that the CCL1-AMFR interaction enhanced CREB/C/EBPβ signaling to promote the macrophage M2 program. Together, our findings reveal that CCL1 acts as a mediator of macrophage M2 polarization and could be a therapeutic target in PF.